Behavioral economic analysis of opioid consumption in heroin-dependent individuals: effects of unit price and pre-session drug supply

Relationship between opioid cross-tolerance during buprenorphine stabilization and return to opioid use during buprenorphine dose tapering

RATIONALE

Opioid injection drug use (IDU) has been linked to a more severe pattern of use (e.g. tolerance, overdose risk) and shorter retention in treatment, which may undermine abstinence attempts.

OBJECTIVES

This secondary data analysis of four human laboratory studies investigated whether current opioid IDU modulates subjective abuse liability responses to high-dose hydromorphone during intermediate-dose buprenorphine stabilization (designed to suppress withdrawal but allow surmountable agonist effects), and whether hydromorphone response magnitude predicts latency of return to opioid use during buprenorphine dose-tapering.

METHODS

Regular heroin users not currently seeking treatment (n = 54; 29 current injectors, 25 non-injectors) were stabilized on 8-mg/day sublingual buprenorphine and assessed for subjective responses (e.g. 'liking', craving) to hydromorphone 24-mg intramuscular challenge (administered 16-hr post-buprenorphine) under randomized, double-blinded, controlled conditions. A subgroup (n = 35) subsequently completed a standardized 3-week outpatient buprenorphine dose-taper, paired with opioid-abstinent contingent reinforcement, and were assessed for return to opioid use based on thrice-weekly urinalysis and self-report.

RESULTS

During buprenorphine stabilization, IDU reported lower 'liking' of buprenorphine and post-hydromorphone peak 'liking', 'good effect' and 'high' compared to non-IDU. Less hydromorphone peak increase-from-baseline in 'liking' (which correlated with less hydromorphone-induced craving suppression) predicted significantly faster return to opioid use during buprenorphine dose-tapering.

CONCLUSIONS

In these buprenorphine-stabilized regular heroin users, IDU is associated with attenuated 'liking' response (more cross-tolerance) to buprenorphine and to high-dose hydromorphone challenge and, in turn, this cross-tolerance (but not IDU) predicts faster return to opioid use. Further research should examine mechanisms that link cross-tolerance to treatment response.

Opioid Risk Tool, in-hospital opioid exposure, and opioid demand predict pain outcomes following traumatic injury

Prescribed opioids are a mainstay pain treatment after traumatic injury, but a subgroup of patients may be at risk for continued opioid use. We evaluated the predictive utility of a traditional screening tool, the Opioid Risk Tool (ORT), and two other measures: average in-hospital milligram morphine equivalents (MME) per day and an assessment of opioid demand in predicting pain outcomes. Assessments of pain-related outcomes (pain intensity, interference, injury-related stress, and need for additional pain treatment) were administered at 2 weeks and 12 months post-discharge in a sample of 34 patients hospitalized for traumatic injury. Bayesian linear models were used to evaluate changes in responses over time as a function of predictors. High-risk ORT, higher MME per day, and greater opioid demand predicted less change in outcomes over time. This report provides first evidence that malleable factors of opioid and opioid demand have utility in predicting pain outcomes following traumatic injury.

Time Cost and Demand: Implications for Public Policy

The success of policy involves not only good design but a good understanding of how the public will respond behaviorally to the benefits or detriments of that policy. Behavioral science has greatly contributed to how we understand the impact of monetary costs on behavior and has therefore contributed to policy design. Consumption taxes are a direct result of this; for example, cigarette taxes that aim to reduce cigarette consumption. In addition to monetary costs, time may also be conceptualized as a constraint on consumption. Time costs may therefore have policy implications, for example, long waiting times could deter people from accessing certain benefits. Recent data show that behavioral economic demand curve methods used to understand monetary cost may also be used to understand time costs. In this article we discuss how the impact of time cost can be conceptualized as a constraint on demand for public benefits utilization and public health when there are delays to receiving the benefits. Policy examples in which time costs may be relevant and demand curve methods may be useful are discussed in the areas of government benefits, public health, and transportation design.

Bidirectional influence of heroin and cocaine escalation in persons with dual opioid and cocaine dependence diagnoses

Persons with dual severe opioid and cocaine use disorders are at risk of considerable morbidity, and the bidirectional relationship of escalation of mu-opioid agonists and cocaine use is not well understood. The aim of this study was to examine the bidirectional relationship between escalation of heroin and cocaine use in volunteers dually diagnosed with opioid and cocaine dependence (OD + CD). Volunteers from New York with OD + CD (total n = 295; male = 182, female = 113; age ≥ 18 years) were interviewed with the Structured Clinical Interview for the DSM-IV Axis I Disorders and Kreek-McHugh-Schluger-Kellogg scales for dimensional measures of drug exposure, which also collect ages of 1st use and onset of heaviest use. Time of escalation was defined as age of onset of heaviest use minus age of 1st use in whole years. Times of escalation of heroin and cocaine were positively correlated in both men (Spearman r = .34, 95% confidence interval [CI: .17, .48], p < .0001) and women (Spearman r = .51, [.27, .50], p < .0001) volunteers. After we adjusted for demographic variables, a Cox regression showed that time of cocaine escalation was a predictor of time of heroin escalation (hazard ratio [HR] = 0.97, 95% CI [0.95, 0.99], p = .003). Another Cox regression showed that this relationship is bidirectional, because time of heroin escalation was also a predictor of time of cocaine escalation (HR = 0.98, [0.96-0.99], p = .016). In these adjusted models, gender was not a significant predictor of time of escalation of either heroin or cocaine. Therefore, escalation did not differ robustly by gender when adjusting for demographics and other major variables. Overall, rapid escalation of cocaine use was a predictor of rapid escalation of heroin use, and vice versa, in persons with dual severe opioid and cocaine use disorders. These findings suggest a shared vulnerability to rapid escalation of these 2 drugs in persons with dual severe opioid and cocaine use disorders. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Shifting North American drug markets and challenges for the system of care

Drug markets are dynamic systems which change based on demand, competition, legislation and revenue. Shifts that are not met with immediate and appropriate responses from the healthcare system can lead to public health crises with tragic levels of morbidity and mortality, as experienced Europe in the early 1990s and as is the case in North America currently. The major feature of the current drug market shift in North America is towards highly potent synthetic opioids such as fentanyl and fentanyl analogues. An additional spike in stimulant use further complicates this issue. Without understanding the ever-changing dynamics of drug markets and consequent patterns of drug use, the healthcare system will continue to be ineffective in its response, and morbidity and mortality will continue to increase. Economic perspectives are largely neglected in research and clinical contexts, but better treatment alternatives need to consider the large-scale macroeconomic conditions of drug markets as well as the behavioural economics of individual substance use. It is important for policy makers, health authorities, first responders and medical providers to be aware of the clinical implications of drug market changes in order to best serve people who use drugs. Only with significant clinical research, a comprehensive reorganization of the system of care across all sectors, and an evidence-driven governance, will we be successful in addressing the challenges brought on by the recent shifts in drug markets.

Behavioral economics and safe sex: Examining condom use decisions from a reinforcer pathology framework

Condom use substantially reduces unwanted pregnancies and sexually transmitted infections. While condom availability is a significant public health priority, effects of condom availability constraints remain relatively under-researched. The limited research on condom availability suggests two major barriers to use: (1) effort/costs and (2) delay to access. To date, we are aware of no study that explores both demand for and discounting of condom availability; the focus of this study was to account for condom decisions using a reinforcement pathology framework. This study used a condom purchase task and the Sexual Delay Discounting Task to quantify behavioral economics of condom use. Low sexual discounting was associated with higher willingness to engage unprotected sex. Demand metrics suggest participants indicating abstinence at condom breakpoint were willing to pay nearly double for condoms relative to individuals indicating unprotected sex at breakpoint. Finally, we grouped participants into reinforcement pathology risk groups based on their discounting and demand indices; these groups significantly differed in self-reported number of sexual partners, unprotected sexual partners, and Sexual Desire scores. This study demonstrates the value of behavioral economic approaches to public health concerns, and further underscores the translational benefits of quantitative metrics to shed novel light on risky health decisions.

Extending stimulus preference assessment with the operant demand framework

This study extended earlier research on stimulus preference (SP) and reinforcer efficacy (RE) using the behavioral economic concept of elasticity. The elasticity of demand for different items can be used to simultaneously compare RE across stimuli and schedules of reinforcement. Highly preferred stimuli were identified via SP assessments and evaluated using progressive-ratio reinforcer assessments. Reinforcers were then evaluated across the ranges of elasticity in individual reinforcer evaluations. Results indicated that schedules associated with the ranges of elasticity (e.g., inelastic vs. elastic) corresponded with rates of the targeted behavior (i.e., work) and these trends were consistent with behavioral economic predictions. These findings encourage further inquiry and replication of operant demand methods to identify potential boundary conditions for stimuli identified using SP assessments. Discussion is provided regarding the efficiency of reinforcer assessment and the utility of schedules found to exist in the elastic and inelastic ranges.

A zero-bounded model of operant demand

Contemporary approaches for evaluating the demand for reinforcers use either the Exponential or the Exponentiated model of operant demand, both derived from the framework of Hursh and Silberberg (2008). This report summarizes the strengths and complications of this framework and proposes a novel implementation. This novel implementation incorporates earlier strengths and resolves existing shortcomings that are due to the use of a logarithmic scale for consumption. The Inverse Hyperbolic Sine (IHS) transformation is reviewed and evaluated as a replacement for the logarithmic scale in models of operant demand. Modeling consumption in the "log₁₀ -like" IHS scale reflects relative changes in consumption (as with a log scale) and accommodates a true zero bound (i.e., zero consumption values). The presence of a zero bound obviates the need for a separate span parameter (i.e., k) and the span of the model may be more simply defined by maximum demand at zero price (i.e., Q₀ ). Further, this reformulated model serves to decouple the exponential rate constant (i.e., α) from variations in span, thus normalizing the rate constant to the span of consumption in IHS units and permitting comparisons when spans vary. This model, called the Zero-bounded Exponential (ZBE), is evaluated using simulated and real-world data. The direct reinstatement ZBE model showed strong correspondence with empirical indicators of demand and with a normalization of α (ZBEn) across empirical data that varied in reinforcing efficacy (dose, time to onset of peak effects). Future directions in demand curve analysis are discussed with recommendations for additional replication and exploration of scales beyond the logarithm when accommodating zero consumption data.

Medications Development for Treatment of Opioid Use Disorder

This review describes methods for preclinical evaluation of candidate medications to treat opioid use disorder (OUD). The review is founded on the propositions that (1) drug self-administration procedures provide the most direct method for assessment of medication effectiveness, (2) procedures that assess choice between opioid and nondrug reinforcers are especially useful, and (3) states of opioid dependence and withdrawal profoundly influence both opioid reinforcement and effects of candidate medications. Effects of opioid medications and vaccines on opioid choice in nondependent and opioid-dependent subjects are reviewed. Various nonopioid medications have also been examined, but none yet have been identified that safely and reliably reduce opioid choice. Future research will focus on (1) strategies for increasing safety and/or effectiveness of opioid medications (e.g., G-protein-biased μ-opioid agonists), and (2) continued development of nonopioid medications (e.g., clonidine) that might serve as adjunctive agents to current opioid medications.

The R package beezdemand: Behavioral Economic Easy Demand

beezdemand: Behavioral Economic Easy Demand, a novel package for performing behavioral economic analyses, is introduced and evaluated. beezdemand extends the statistical program to facilitate many of the analyses performed in studies of behavioral economic demand. The package supports commonly used options for modeling operant demand and performs data screening, fits models of demand, and calculates numerous measures relevant to applied behavioral economists. The free and open source beezdemand package is compared to commercially available software (i.e., GraphPad Prism™) using peer-reviewed and simulated data. The results of this study indicated that beezdemand provides results consistent with commonly used commercial software but provides a wider range of methods and functionality desirable to behavioral economic researchers. A brief overview of the package is presented, its functionality is demonstrated, and considerations for its use are discussed.

Relative Bioavailability, Intranasal Abuse Potential, and Safety of Benzhydrocodone/Acetaminophen Compared with Hydrocodone Bitartrate/Acetaminophen in Recreational Drug Abusers

Objectives

Benzhydrocodone is a hydrocodone prodrug that has been combined with acetaminophen (APAP) in a novel immediate-release analgesic. This study evaluated the relative bioavailability, intranasal abuse potential, and safety of benzhydrocodone/APAP compared with commercially available hydrocodone bitartrate (HB)/APAP.

Design

Single-center, randomized, double-blind, double-dummy, two-part study comprising a Dose Selection (Part A) phase and a Main Study (Part B) phase.

Setting

Clinical research site.

Subjects

Healthy adult, nondependent, recreational opioid users with a history of intranasal abuse.

Methods

Subjects (N = 42) in Part B received five in-clinic treatments consisting of intranasal and oral benzhydrocodone/APAP (13.34/650 mg), intranasal and oral hydrocodone/APAP (15/650 mg), and placebo, with four or more days of washout between treatments. Pharmacodynamic assessments included subjective effects of Drug Liking, Overall Drug Liking, and Take Drug Again (assessed on visual analog scale [VAS]), as well as nasal irritation. Pharmacokinetics and safety were also assessed.

Results

Hydrocodone C_max was 11% lower for intranasal benzhydrocodone/APAP vs intranasal HB/APAP (P = 0.0027). Early cumulative hydrocodone exposures for intranasal benzhydrocodone/APAP through 0.5, 1, and 2 hours were reduced by approximately 50%, 29%, and 15%, respectively (P ≤ 0.0024). Correspondingly, Drug Liking VAS values up to two hours postdose were significantly lower for intranasal benzhydrocodone/APAP vs intranasal HB/APAP (P ≤ 0.0079), although peak Drug Liking VAS (E_max) scores were not different (P = 0.2814). Adverse nasal effects were more frequent for intranasal benzhydrocodone/APAP vs intranasal HB/APAP.

Conclusions

Reduced hydrocodone exposure and drug liking at early time intervals, coupled with adverse nasal effects, can be expected to provide a level of deterrence to the intranasal route of abuse for benzhydrocodone/APAP.

Locomotor activity does not predict individual differences in morphine self-administration in rats

Understanding factors contributing to individual differences in opioid addiction vulnerability is essential for developing more effective preventions and treatments. Sensation seeking has been implicated in addiction to several drugs of abuse, yet its relationship with individual differences in opioid addiction vulnerability has not been well established. The primary goal of this study was to evaluate the relationship between locomotor activity in a novel environment, a preclinical model of sensation-seeking, and individual differences in acquisition of i.v. morphine self-administration (SA) in rats. A secondary goal was to evaluate the relationship between activity and elasticity of demand (reinforcing efficacy) for morphine measured using a behavioral economic approach. Following an initial locomotor activity screen, animals were allowed to acquire morphine SA at a unit dose of 0.5 mg/kg/infusion in 4 hour/day sessions (Experiment 1) or 0.2 mg/kg/infusion in 2 hour/day sessions (Experiment 2) until infusion rates were stable. Unit price was subsequently manipulated via progressive reductions in unit dose (Experiment 1) or increases in response requirement per infusion (Experiment 2). Activity levels were not correlated with acquisition of morphine SA in either experiment. Morphine consumption was generally well described by an exponential demand function in both experiments (R² values > 0.95 for rats as a group), but activity did not correlate with behavioral economic measures. Locomotor activity in a novel environment did not predict individual differences in acquisition of morphine SA. These data complement findings from some human studies and suggest that the role of sensation seeking in individual differences in opioid addiction vulnerability may be limited.

Clinical models of decision making in addiction

As research on decision making in addiction accumulates, it is increasingly clear that decision-making processes are dysfunctional in addiction and that this dysfunction may be fundamental to the initiation and maintenance of addictive behavior. How drug-dependent individuals value and choose among drug and nondrug rewards is consistently different from non-dependent individuals. The present review focuses on the assessment of decision-making in addiction. We cover the common behavioral tasks that have shown to be fruitful in decision-making research and highlight analytical and graphical considerations, when available, to facilitate comparisons within and among studies. Delay discounting tasks, drug demand tasks, drug choice tasks, the Iowa Gambling Task, and the Balloon Analogue Risk Task are included.

Novel Therapeutics for Addiction: Behavioral and Neuroeconomic Approaches

The maturing fields of behavioral- and neuro-economics provides conceptual understanding of the Competing Neurobehavioral Decision Systems theory (CNDS) and reinforcer pathology (i.e. high valuation of and excessive preference for drug reinforcers) allowing us to coherently categorize treatments into a theoretically comprehensive framework of addiction. In this chapter, we identify and clarify how existing and novel interventions can ameliorate reinforcer pathology in light of the CNDS and be leveraged to treat addiction.

Sustained-Release Buprenorphine (RBP-6000) Blocks the Effects of Opioid Challenge With Hydromorphone in Subjects With Opioid Use Disorder

A major goal for the treatment of opioid use disorder is to reduce or eliminate the use of illicit opioids. Buprenorphine, a μ-opioid receptor partial agonist and kappa opioid receptor antagonist, is now being developed as a monthly, sustained-release formulation (RBP-6000). The objective of this study was to demonstrate that RBP-6000 blocks the subjective effects and reinforcing efficacy of the μ-opioid receptor agonist hydromorphone (intramuscularly administered) in subjects with moderate or severe opioid use disorder. Subjects were first inducted and dose stabilized on sublingual buprenorphine/naloxone (8-24 mg daily; dose expressed as the buprenorphine component), then received two subcutaneous injections of RBP-6000 (300 mg) on Day 1 and Day 29. Hydromorphone challenges (6 mg, 18 mg or placebo administered in randomized order) occurred on 3 consecutive days of each study week before and after receiving RBP-6000. Subjects reported their responses to each challenge on various 100-mm Visual Analogue Scales (VAS). Subjects also completed a choice task to assess the reinforcing efficacy of each hydromorphone dose relative to money. At baseline, mean "drug liking" VAS scores for hydromorphone 18 mg and 6 mg versus placebo were 61 mm (95% confidence interval, 52.3-68.9) and 45 mm (95% confidence interval, 37.2-53.6), respectively. After 300 mg RBP-6000 was administered, mean VAS score differences from placebo were less than 10 mm through week 12. The reinforcing efficacy of hydromorphone decreased in a parallel manner. This study demonstrated that RBP-6000 at a 300 mg dose provides durable and potent blockade of the subjective effects and reinforcing efficacy of hydromorphone in subjects with moderate or severe opioid use disorder.

Functional mu opioid receptor polymorphism (OPRM1 A(118) G) associated with heroin use outcomes in Caucasian males: A pilot study

BACKGROUND

Heroin's analgesic, euphoric and dependence-producing effects are primarily mediated by the mu opioid receptor (MOR). A single gene, OPRM1, encodes the MOR. The functional polymorphism A(118)G, located in exon 1 of the OPRM1 gene, results in anatomically-specific reductions in MOR expression, which may alter an individual's response to heroin. In prior studies 118G (rare allele) carriers demonstrated significantly greater opioid tolerance, overdose vulnerability, and pain sensitivity than 118AA homozygotes. Those findings suggest OPRM1 genotype may impact characteristics of heroin use.

METHODS

The present pilot study characterized the impact of OPRM1 genotype (rs1799971, 118G allele carriers vs. 118AA homozygotes) on heroin-use phenotypes associated with heroin dependence severity in a sample of male, Caucasian chronic heroin users (n = 86).

RESULTS

Results indicate that 118G allele carriers reported significantly more heroin use-related consequences and heroin-quit attempts, and were more likely to have sought treatment for their heroin use than 118AA homozygotes.

CONCLUSIONS

These preliminary findings, consistent with extant data, illustrate a role for OPRM1 allelic variation on heroin use characteristics, and provide support for considering genotype in heroin treatment and relapse prevention.

Using behavioral economics to predict opioid use during prescription opioid dependence treatment

BACKGROUND

Research grounded in behavioral economics has previously linked addictive behavior to disrupted decision-making and reward-processing, but these principles have not been examined in prescription opioid addiction, which is currently a major public health problem. This study examined whether pre-treatment drug reinforcement value predicted opioid use during outpatient treatment of prescription opioid addiction.

METHODS

Secondary analyses examined participants with prescription opioid dependence who received 12 weeks of buprenorphine-naloxone and counseling in a multi-site clinical trial (N=353). Baseline measures assessed opioid source and indices of drug reinforcement value, including the total amount and proportion of income spent on drugs. Weekly urine drug screens measured opioid use.

RESULTS

Obtaining opioids from doctors was associated with lower pre-treatment drug spending, while obtaining opioids from dealers/patients was associated with greater spending. Controlling for demographics, opioid use history, and opioid source frequency, patients who spent a greater total amount (OR=1.30, p<.001) and a greater proportion of their income on drugs (OR=1.31, p<.001) were more likely to use opioids during treatment.

CONCLUSIONS

Individual differences in drug reinforcement value, as indicated by pre-treatment allocation of economic resources to drugs, reflects propensity for continued opioid use during treatment among individuals with prescription opioid addiction. Future studies should examine disrupted decision-making and reward-processing in prescription opioid users more directly and test whether reinforcer pathology can be remediated in this population.

Revisiting the role of the urban environment in substance use: the case of analgesic overdose fatalities

OBJECTIVES

We examined whether neighborhood social characteristics (income distribution and family fragmentation) and physical characteristics (clean sidewalks and dilapidated housing) were associated with the risk of fatalities caused by analgesic overdose.

METHODS

In a case-control study, we compared 447 unintentional analgesic opioid overdose fatalities (cases) with 3436 unintentional nonoverdose fatalities and 2530 heroin overdose fatalities (controls) occurring in 59 New York City neighborhoods between 2000 and 2006.

RESULTS

Analgesic overdose fatalities were less likely than nonoverdose unintentional fatalities to have occurred in higher-income neighborhoods (odds ratio [OR] = 0.82; 95% confidence interval [CI] = 0.70, 0.96) and more likely to have occurred in fragmented neighborhoods (OR = 1.35; 95% CI = 1.05, 1.72). They were more likely than heroin overdose fatalities to have occurred in higher-income (OR = 1.31; 95% CI = 1.12, 1.54) and less fragmented (OR = 0.71; 95% CI = 0.55, 0.92) neighborhoods.

CONCLUSIONS

Analgesic overdose fatalities exhibit spatial patterns that are distinct from those of heroin and nonoverdose unintentional fatalities. Whereas analgesic fatalities typically occur in lower-income, more fragmented neighborhoods than nonoverdose fatalities, they tend to occur in higher-income, less unequal, and less fragmented neighborhoods than heroin fatalities.

BDNF Val(66)Met genotype is associated with drug-seeking phenotypes in heroin-dependent individuals: a pilot study

Brain-derived neurotrophic factor (BDNF) Val(66)Met genotype has been associated with neurobehavioral deficits. To examine its relevance for addiction, we examined BDNF genotype differences in drug-seeking behavior. Heroin-dependent volunteers (n = 128) completed an interview that assessed past-month naturalistic drug-seeking/use behaviors. In African Americans (n = 74), the Met allele was uncommon (carrier frequency 6.8%); thus, analyses focused on European Americans (n = 54), in whom the Met allele was common (carrier frequency 37.0%). In their natural setting, Met carriers (n = 20) reported more time- and cost-intensive heroin-seeking and more cigarette use than Val homozygotes (n = 34). BDNF Val(66)Met genotype predicted 18.4% of variance in 'weekly heroin investment' (purchasing time × amount × frequency). These data suggest that the BDNF Met allele may confer a 'preferred drug-invested' phenotype, resistant to moderating effects of higher drug prices and non-drug reinforcement. These preliminary hypothesis-generating findings require replication, but are consistent with pre-clinical data that demonstrate neurotrophic influence in drug reinforcement. Whether this genotype is relevant to other abused substances besides opioids or nicotine, or treatment response, remains to be determined.

Prescription opioid mortality trends in New York City, 1990-2006: examining the emergence of an epidemic

BACKGROUND

The drug overdose mortality rate tripled between 1990 and 2006; prescription opioids have driven this epidemic. We examined the period 1990-2006 to inform our understanding of how the current prescription opioid overdose epidemic emerged in urban areas.

METHODS

We used data from the Office of the Chief Medical Examiner to examine changes in demographic and spatial patterns in overdose fatalities induced by prescription opioids (i.e., analgesics and methadone) in New York City (NYC) in 1990-2006, and what factors were associated with death from prescription opioids vs. heroin, historically the most prevalent form of opioid overdose in urban areas.

RESULTS

Analgesic-induced overdose fatalities were the only types of overdose fatalities to increase in 1990-2006 in NYC; the fatality rate increased sevenfold from 0.39 in 1990 to 2.7 per 100,000 persons in 2006. Whites and Latinos were the only racial/ethnic groups to exhibit an increase in overdose-related mortality. Relative to heroin overdose decedents, analgesic and methadone overdose decedents were more likely to be female and to concurrently use psychotherapeutic drugs, but less likely to concurrently use alcohol or cocaine. Analgesic overdose decedents were less likely to be Black or Hispanic, while methadone overdose decedents were more likely to be Black or Hispanic in contrast to heroin overdose decedents.

CONCLUSIONS

The distinct epidemiologic profiles exhibited by analgesic and methadone overdose fatalities highlight the need to define drug-specific public health prevention efforts.

Nicotine reduction: strategic research plan

BACKGROUND

Reducing nicotine content in cigarettes and other combustible products to levels that are not reinforcing or addictive has the potential to substantially reduce tobacco-related morbidity and mortality. The authority to reduce nicotine levels as a regulatory measure is provided in the U.S. Family Smoking Prevention and Tobacco Control Act and is consistent with the general regulatory powers envisioned under the relevant articles of the World Health Organization's Framework Convention on Tobacco Control. Many experts have considered reducing nicotine in cigarettes to be a feasible national policy approach, but more research is necessary.

PURPOSE

This article describes proceedings from a conference that had the goals of identifying specific research gaps, describing methods and measures to consider for addressing these gaps, and considering ways to foster collaboration.

RESULTS AND CONCLUSION

Identified research gaps included determining the dose of nicotine that would be optimal for reducing and extinguishing cigarette use, examining approaches for reducing nicotine levels in the general and special populations of smokers, understanding how constituents other than nicotine may contribute to the reinforcing effects of tobacco, and identifying unintended consequences to determine ways to mitigate them. Methods that can be used ranged from brain imaging to large human clinical trials. The development and availability of valid biomarkers of exposure and effect are important. Infrastructures to facilitate collaboration need to be established.

Yohimbine increases opioid-seeking behavior in heroin-dependent, buprenorphine-maintained individuals

RATIONALE

In laboratory animals, the biological stressor yohimbine (α(2)-noradrenergic autoreceptor antagonist) promotes drug seeking. Human laboratory studies have demonstrated that psychological stressors can increase drug craving but not that stressors alter drug seeking.

OBJECTIVES

This clinical study tested whether yohimbine increases opioid-seeking behavior.

METHODS

Ten heroin-dependent, buprenorphine-stabilized (8 mg/day) volunteers sampled two doses of hydromorphone [12 and 24 mg IM in counterbalanced order, labeled drug A (session 1) and drug B (session 2)]. During each of six later sessions (within-subject, double-blind, randomized crossover design), volunteers could respond on a 12-trial choice progressive ratio task to earn units (1 or 2 mg) of the sampled hydromorphone dose (drug A or B) vs money ($2) following different oral yohimbine pretreatment doses (0, 16.2, and 32.4 mg).

RESULTS

Behavioral economic demand intensity and peak responding (O (max)) were significantly higher for hydromorphone 2 than 1 mg. Relative to placebo, yohimbine significantly increased hydromorphone demand inelasticity, more so for hydromorphone 1-mg units (P (max) = 909, 3,647, and 3,225 for placebo, 16.2, and 32.4 mg yohimbine doses, respectively) than hydromorphone 2-mg units (P (max) = 2,656, 3,193, and 3,615, respectively). Yohimbine produced significant but clinically modest dose-dependent increases in blood pressure (systolic ≈ 15 and diastolic ≈ 10 mmHg) and opioid withdrawal symptoms, and decreased opioid agonist symptoms and elated mood.

CONCLUSIONS

These findings concur with preclinical data by demonstrating that yohimbine increases drug seeking; in this study, these effects occurred without clinically significant subjective distress or elevated craving, and partly depended on opioid unit dose.

Interaction between behavioral and pharmacological treatment strategies to decrease cocaine choice in rhesus monkeys

Behavioral and pharmacotherapeutic approaches constitute two prominent strategies for treating cocaine dependence. This study investigated interactions between behavioral and pharmacological strategies in a preclinical model of cocaine vs food choice. Six rhesus monkeys, implanted with a chronic indwelling double-lumen venous catheter, initially responded under a concurrent schedule of food delivery (1-g pellets, fixed-ratio (FR) 100 schedule) and cocaine injections (0-0.1 mg/kg/injection, FR 10 schedule) during continuous 7-day treatment periods with saline or the agonist medication phenmetrazine (0.032-0.1 mg/kg/h). Subsequently, the FR response requirement for cocaine or food was varied (food, FR 100; cocaine, FR 1-100; cocaine, FR 10; food, FR 10-300), and effects of phenmetrazine on cocaine vs food choice were redetermined. Decreases in the cocaine FR or increases in the food FR resulted in leftward shifts in the cocaine choice dose-effect curve, whereas increases in the cocaine FR or decreases in the food FR resulted in rightward shifts in the cocaine choice dose-effect curve. The efficacy of phenmetrazine to decrease cocaine choice varied systematically as a function of the prevailing response requirements, such that phenmetrazine efficacy was greatest when cocaine choice was maintained by relatively low unit cocaine doses. These results suggest that efficacy of pharmacotherapies to modulate cocaine use can be influenced by behavioral contingencies of cocaine availability. Agonist medications may be most effective under contingencies that engender choice of relatively low cocaine doses.

Medications development for opioid abuse

Here we describe methods for preclinical evaluation of candidate medications to treat opioid abuse and dependence. Our perspective is founded on the propositions that (1) drug self-administration procedures provide the most direct method for assessment of medication effects, (2) procedures that assess choice between opioid and nondrug reinforcers are especially useful, and (3) the states of opioid dependence and withdrawal profoundly influence both opioid reinforcement and the effects of candidate medications. Effects of opioid medications on opioid choice in nondependent and opioid-dependent subjects are reviewed. Various nonopioid medications have also been examined, but none yet have been identified that safely and reliably reduce opioid choice. Future research will focus on (1) strategies for increasing safety and/or effectiveness of opioid medications, and (2) continued development of nonopioids such as inhibitors of endocannabinoid catabolic enzymes or inhibitors of opioid-induced glial activation.

Motivational assessment of non-treatment buprenorphine research participation in heroin dependent individuals

BACKGROUND

Heroin abuse remains an important public health problem, particularly in economically disadvantaged areas. Insight into this problem is gained from interviewing addicted individuals. However, we lack systematic data on factors that motivate heroin users to participate in non-treatment research that offers both financial incentives (compensation) and non-financial incentives (e.g., short-term medication).

AIM

To better understand the relative importance of several types of personal motivations to participate in non-treatment buprenorphine research, and to relate self-motivations to social, economic, demographic and drug use factors.

METHODS

Heroin dependent volunteers (N=235 total; 57 female and 178 male; 136 African American, 86 Caucasian, and 13 Other) applied for non-therapeutic buprenorphine research in an urban outpatient setting from 2004 to 2008. We conducted a semi-structured behavioral economic interview, after which participants ranked 11 possible motivations for research participation.

RESULTS

Although the study was repeatedly described as non-treatment research involving buprenorphine, participants often ranked some treatment-related motivations as important (wanting to reduce/stop heroin use, needing a medication to get stabilized/detoxify). Some motivations correlated with income, heroin use, and years since marketing of buprenorphine. Two dimensions emerged from principal component analysis of motivation rankings: (1) treatment motivation vs. greater immediate needs and (2) commitment to trying alternatives vs. a more accepting attitude toward traditional interventions. In summary, heroin addicts' self-motivations to engage in non-therapeutic research are complex--they value economic gain but not exclusively or primarily--and relate to variables such as socioeconomic factors and drug use.

Cigarette demand and delayed reward discounting in nicotine-dependent individuals with schizophrenia and controls: an initial study

RATIONALE

The high prevalence of smoking and low cessation rates among individuals with schizophrenia and similar conditions are not well understood. Behavioral economics has been extensively applied to studying addictive behavior and may contribute to understanding smoking in this subpopulation.

OBJECTIVES

This study compared smokers with schizophrenia or schizoaffective disorder (SS) and control smokers (CS) on indices of cigarette demand and delayed reward discounting, a behavioral economic index of impulsivity.

MATERIALS AND METHODS

The SS (n=25) and CS (n=24) groups participated in two sessions approximately 1 week apart. During the first session, delay discounting was assessed using the Monetary Choice Questionnaire. During the second session, participants smoked their usual brand ad libitum through a smoking topography assessment device, after which cigarette demand was assessed using a cigarette purchase task. Primary comparisons were of the hyperbolic discounting function, k, and indices of cigarette demand.

RESULTS

Compared to the CS group, the SS group exhibited significantly higher intensity of demand, and significantly greater consumption and expenditure across the inelastic portion of the demand curve, but no differences were evident on the other demand indices. No differences were evident for delay discounting. The SS group also exhibited heavier smoking topography and two indices of smoking topography were significantly correlated with demand.

CONCLUSIONS

These results provide further evidence of higher incentive value of cigarettes among SS individuals, but not greater impulsivity, as measured by discounting. Considerations include potentially important methodological factors and the role of satiation/withdrawal.

A novel IV cocaine self-administration procedure in rats: differential effects of dopamine, serotonin, and GABA drug pre-treatments on cocaine consumption and maximal price paid

RATIONALE

Behavior occurring during cocaine self-administration can be classified as either consummatory or appetitive. These two concepts are usually addressed independently using separate reinforcement schedules. For example, appetitive behavior can be assessed with a progressive ratio schedule, whereas consummatory behavior is typically measured using a fixed ratio schedule.

OBJECTIVES

Depending on the schedule used, it is often difficult to determine whether a particular drug pretreatment is affecting self-administration through an effect on appetitive responding, consummatory responding, or perhaps both. In the present study, we tested the effect of pretreating rats with four different drugs on appetitive and consummatory behaviors.

MATERIALS AND METHODS

We recently developed a technique that provides an independent assessment of both behavioral concepts within the same experimental session. In this threshold procedure, rats are offered a descending series of 11 unit doses (422-1.3 μg/injection) during consecutive timed intervals under a fixed-ratio schedule. Consummatory behavior can be analyzed by assessing intake at high unit doses; an estimate of appetitive responding can be determined from responding occurring at the threshold dose. Applying behavioral economics to these data provides dependent measures of consumption when minimally constrained by price and the maximal price paid (P (max)) for cocaine.

RESULTS

Haloperidol increased cocaine consumption when minimally constrained by price but decreased P (max). In contrast, D: -amphetamine increased P (max). Fluoxetine decreased P (max) and consumption when minimally constrained by price. Baclofen selectively decreased P (max).

CONCLUSIONS

These data suggest that drug pretreatments can alter consummatory and appetitive behavior differently because each concept involves distinct neural mechanisms.

Sustained release d-amphetamine reduces cocaine but not 'speedball'-seeking in buprenorphine-maintained volunteers: a test of dual-agonist pharmacotherapy for cocaine/heroin polydrug abusers

The aim of this study was to determine whether oral sustained release d-amphetamine (SR-AMP) reduces cocaine and opioid/cocaine combination ('speedball'-like) seeking in volunteers with current opioid dependence and cocaine dependence. Following outpatient buprenorphine (BUP) 8 mg/day stabilization without SR-AMP, eight participants completed a 3-week in-patient study with continued BUP 8 mg/day maintenance and double-blind ascending SR-AMP weekly doses of 0, 30, and 60 mg/day, respectively. After 3 days (Saturday-Monday) stabilization at each SR-AMP weekly dose (0, 15, or 30 mg administered at 0700 and 1225 each day), on Tuesday-Friday mornings (0900-1200 hours), participants sampled four drug combinations in randomized, counterbalanced order under double-blind, double-dummy (intranasal cocaine and intramuscular hydromorphone) conditions: cocaine (COC 100 mg+saline); hydromorphone (COC 4 mg+HYD 24 mg); 'speedball' (COC 100 mg+HYD 24 mg); and placebo (COC 4 mg+saline). Subjective and physiological effects of these drug combinations were measured. From 1230 to 1530 hours, participants could respond on a choice, 12-trial progressive ratio schedule to earn drug units (1/12th of total morning dose) or money units (US$2). SR-AMP significantly reduced COC, but not HYD or speedball, choices and breakpoints. SR-AMP also significantly reduced COC subjective (eg, abuse-related) effects and did not potentiate COC-induced cardiovascular responses. This study shows the ability of SR-AMP to attenuate COC self-administration, as well as its selectivity, in cocaine/heroin polydrug abusers. Further research is warranted to ascertain whether SR-AMP combined with BUP could be a useful dual-agonist pharmacotherapy.

Effects of experimental Unemployment, Employment and Punishment analogs on opioid seeking and consumption in heroin-dependent volunteers

This study investigated the extent to which hydromorphone (HYD) choice and behavioral economic demand differed during experimental analogs of Unemployment (Drug Only: HYD and no money alternative), Employment (Drug or Money: HYD and $4 alternative), and Punishment (Drug Only+Money Loss: HYD only and $4 subtracted for each HYD choice), in the context of anticipated high vs. low post-session drug availability (HYD 24 mg vs. placebo). Eleven heroin-dependent, buprenorphine-stabilized (8 mg/day) volunteers first sampled two HYD doses (0 and 24 mg IM in randomized, counterbalanced order, labeled Drug A [session 1] and Drug B [session 2]). In each of the final six sessions, volunteers were given access to a 12-trial choice progressive ratio (PR) task and could work to receive HYD unit doses (2mg each); cumulative dose units earned were administered in a bolus injection after the work session. Before the PR task, volunteers were told which HYD dose (Drug A or B) would be available 3h after the PR-contingent injection. Relative to Unemployment (Drug Only), Employment (Drug or Money) and Punishment (Drug Only+Money Loss) each significantly suppressed HYD seeking (e.g., breakpoints). Employment and Punishment also reduced HYD behavioral economic demand, but via different mechanisms: Employment increased HYD price-elasticity, whereas Punishment decreased HYD demand intensity. Adjusting for the initial level difference (i.e., normalized demand), Employment significantly decreased P(max) (i.e., lower "essential value" of HYD) and O(max) (maximum HYD responding) compared to Punishment or Unemployment. These effects were not significantly altered by post-session drug availability.

Risk factors for craving and relapse in heroin users treated with oral or implant naltrexone

BACKGROUND

Oral naltrexone effectively antagonizes heroin, but patient noncompliance limits its utility; sustained-release preparations may overcome this. Few data are available on optimal blood naltrexone levels for preventing craving and/or return to heroin use. This study assesses various risk factors, including blood naltrexone level, for heroin craving and relapse to illicit opioids.

METHODS

Heroin-dependent persons from a randomized controlled trial of oral versus implant naltrexone were followed up for 6 months. Thirty-four participants received 50 mg oral naltrexone daily, plus placebo implant; thirty-five participants received a single dose of 2.3 g naltrexone implant, plus daily oral placebo tablets.

RESULTS

Compared to oral naltrexone patients, implant naltrexone patients were significantly less likely to use any opioids and had one-fifth the risk of using heroin > or = weekly. Risk of > or = weekly heroin use increased by 2.5 times at blood naltrexone concentration < .5 ng/mL compared with > or = .5 ng/mL, with 3 ng/mL associated with very low risk of use. Craving remained near "floor" levels for implant patients but rebounded to higher levels among oral patients. Lower craving scores (< or = 20/70) predicted lower relapse risk. Noncompliance with daily oral formula, higher baseline craving, longer history of use, and being younger predicted higher craving at follow-up.

CONCLUSIONS

Implant naltrexone was better associated with reduced heroin craving and relapse than oral naltrexone. Effective treatment was achieved at blood naltrexone levels of 1 ng/mL to 3 ng/mL, with higher levels associated with greater efficacy. Craving assessment may be valuable in predicting relapse risk allowing timely intervention.

Alcohol demand, delayed reward discounting, and craving in relation to drinking and alcohol use disorders

A behavioral economic approach to alcohol use disorders (AUDs) emphasizes both individual and environmental determinants of alcohol use. The current study examined individual differences in alcohol demand (i.e., motivation for alcohol under escalating conditions of price) and delayed reward discounting (i.e., preference for immediate small rewards compared to delayed larger rewards) in 61 heavy drinkers (62% with an AUD). In addition, based on theoretical accounts that emphasize the role of craving in reward valuation and preferences for immediate rewards, craving for alcohol was also examined in relation to these behavioral economic variables and the alcohol-related variables. Intensity of alcohol demand and delayed reward discounting were significantly associated with AUD symptoms, but not with quantitative measures of alcohol use, and were also moderately correlated with each other. Likewise, craving was significantly associated with AUD symptoms, but not with alcohol use, and was also significantly correlated with both intensity of demand and delayed reward discounting. These findings further emphasize the relevance of behavioral economic indices of motivation to AUDs and the potential importance of craving for alcohol in this relationship.

Behavioral economic analysis of opioid consumption in heroin-dependent individuals: effects of alternative reinforcer magnitude and post-session drug supply

This study investigated the extent to which hydromorphone (HYD) choice and behavioral economic demand were influenced by HYD unit price (UP), alternative money reinforcement magnitude and post-session HYD supply. Heroin-dependent research volunteers (n=13) stabilized on buprenorphine 8 mg/day first sampled two HYD doses (12 and 24 mg IM, labeled Drug A [session 1] and Drug B [session 2]). In each of the final six sessions, volunteers were given access to a 12-trial choice progressive ratio (PR) task and could earn a HYD unit dose (2 mg, fixed) or money ($2 or $4, varied across sessions), administered immediately after the work session. Before the PR task, volunteers were told which HYD supplemental dose (none, Drug A or B) would be available 3h after receiving the PR-contingent dose. PR-contingent HYD choice significantly decreased when $4 relative to $2 was concurrently available. Information about the post-session HYD supplement moderated this effect: when subjects were told a supplemental dose was available, HYD-seeking behavior decreased when the money alternative was smaller ($2), but this information did not further attenuate HYD choice, which was already low, when the money alternative was higher ($4). HYD demand elasticity was only increased by the $4 relative to $2 alternative without the HYD supplement. In summary, opioid-seeking behavior is influenced by the availability of concurrent non-drug and drug alternatives. These findings show that drug availability and non-drug alternatives interact to modulate drug-seeking behavior.

Opioid abstinence reinforcement delays heroin lapse during buprenorphine dose tapering

A positive reinforcement contingency increased opioid abstinence during outpatient dose tapering (4, 2, then 0 mg/day during Weeks 1 through 3) in non-treatment-seeking heroin-dependent volunteers who had been maintained on buprenorphine (8 mg/day) during an inpatient research protocol. The control group (n=12) received $4.00 for completing assessments at each thrice-weekly visit during dose tapering; 10 of 12 lapsed to heroin use 1 day after discharge. The abstinence reinforcement group (n=10) received $30.00 for each consecutive opioid-free urine sample; this significantly delayed heroin lapse (median, 15 days).

Latent structure of facets of alcohol reinforcement from a behavioral economic demand curve

RATIONALE

Behavioral economic demand curves are quantitative representations of the relationship between consumption of a drug and its cost. Demand curves provide a multidimensional assessment of reinforcement, but the relationships among the various indices of reinforcement have been largely unstudied.

OBJECTIVES

The objective of the study is to use exploratory factor analysis to examine the underlying factor structure of the facets of alcohol reinforcement generated from an alcohol demand curve.

MATERIALS AND METHODS

Participants were 267 weekly drinkers [76% female; age M = 20.11 (SD = .1.51); drinks/week M = 14.33 (SD = 11.82)] who underwent a single group assessment session. Alcohol demand curves were generated via an alcohol purchase task, which assessed consumption at 14 levels of prices from $0 to $9. Five facets of demand were generated from the measure [intensity, elasticity, P (max) (maximum inelastic price), O (max) (maximum alcohol expenditure), and breakpoint], using both observed and derived calculations. Principal components analysis was used to examine the latent structure among the variables.

RESULTS

The results revealed a clear two-factor solution, which were interpreted as "Persistence," reflecting sensitivity to escalating price, and "Amplitude," reflecting the amount consumed and spent. The two factors were generally quantitatively distinct, although O (max) loaded on both.

CONCLUSIONS

These findings suggest that alcohol reinforcement as measured via a demand curve is binary in nature, with separate dimensions of price-sensitivity and volumetric consumption. If supported, these findings may contribute theoretically and experimentally to a reinforcement-based approach to alcohol use and misuse.

Behavioral economic assessment of price and cocaine consumption following self-administration histories that produce escalation of either final ratios or intake

Various self-administration procedures are being developed to model specific aspects of the addiction process. For example, 'increased cocaine intake over time' has been modeled by providing long access (LgA) to cocaine during daily self-administration sessions under a fixed-ratio (FR1) reinforcement schedule. In addition, 'increased time and energy devoted to acquire cocaine' has been modeled by providing access to cocaine during daily self-administration sessions under a progressive-ratio (PR) schedule. To investigate the distinctiveness of these models, the behavioral economics variables of consumption and price were applied to cocaine self-administration data. To assess changes in consumption and price, cocaine self-administration was tested across a descending series of doses (0.237-0.001 mg per injection) under an FR1 reinforcement schedule to measure drug intake in the high dose range and thresholds in the low range. Cocaine consumption remained relatively stable across doses until a threshold was reached, at which maximal responding was observed. It was found that a history of LgA training produced an increase in cocaine consumption; whereas a history of PR training produced an increase in the maximal price (P(max)) expended for cocaine. Importantly, the concepts of consumption and price were found to be dissociable. That is, LgA training produced an increase in consumption but a decrease in P(max), whereas PR training produced an increase in P(max) without increasing consumption. These results suggest that distinct aspects of the addiction process can be parsed using self-administration models, thereby facilitating the investigation of specific neurobiological adaptations that occur through the addiction process.

Effects of reinforcer magnitude and alternative reinforcer delay on preference for alcohol during a multiple-choice procedure

The Multiple-Choice Procedure [MCP; Griffiths, R.R., Troisi II, J.R., Silverman, K., Mumford, G.K., 1993. Multiple-choice procedure: an efficient approach for investigating drug reinforcement in humans. Behav. Pharmacol. 4, 3-13; Griffiths, R.R., Rush, C.R., Puhala, K.A., 1996. Validation of the multiple-choice procedure for investigating drug reinforcement in humans. Behav. Pharmacol. 4, 3-13] was developed to investigate the relationship between drug preferences and alternative reinforcers. The current study was designed to better characterize the relationships among reinforcer magnitude, delay associated with an alternative reinforcer, and preference for alcohol among a sample of undergraduate drinkers. Participants were 27 male undergraduates, over the age of 21, who reported engaging in at least three occasions of binge drinking over the previous month. All participants took part in a single laboratory session, during which six versions of the MCP questionnaire were administered. Across the versions, participants made a total of 180 discrete choices between three amounts of alcohol (12, 24, or 36 ounces of beer; deception was used to mask the fact that 36 ounces of beer would not actually be provided during the sessions) and escalating amounts of money ($0 to $20) delivered immediately or after a one-week delay. Response on the MCP varied as a function of the amount of alcohol available and the delay associated with the alternative monetary reinforcer, with the effect of the delay diminishing as the dose of alcohol increased. Results of the current study are consistent with previous laboratory studies of choice behavior and with behavioral economic theories of substance use.

Supply of a nondrug substitute reduces escalated heroin consumption

Escalation of drug consumption-a hallmark of addiction-has been hypothesized to be associated with a relative devaluation of alternative nondrug rewards and thus with a decrease in their ability to compete with or to substitute for the drug. In a behavioral economic framework, decreased substitutability of nondrug rewards for drug would explain why drug consumption is behaviorally dominant and relatively resistant to change (eg price-inelastic) in drug-addicted individuals. The goal of the present study was to test this hypothesis using a validated rat model of heroin intake escalation. Escalation was precipitated by long (6 h, long access (LgA)), but not short (1 h, short access (ShA)), daily access to i.v. heroin self-administration. After escalation, the effects of price (ie fixed-ratio value) on heroin consumption were assessed under two alternative reward conditions: in the presence or absence of a nondrug substitute for heroin (ie four freely available chow pellets). As expected, escalated heroin consumption by LgA rats was less sensitive to price than heroin consumption by ShA rats, showing that heroin had acquired greater reinforcing strength during escalation. However, supplying a substitute during access to heroin was sufficient to reverse this post-escalation increase in the reinforcing effectiveness of heroin. Thus, escalated heroin consumption is not associated with a decreased sensitivity to competing nondrug rewards. Escalated drug use may therefore persist, not so much because of a relative devaluation of nondrug substitutes, but because of a loss or reduction of their availability.

Drug preference in cocaine and alcohol dual-dependent patients

The present study extended previous work with the multiple-choice procedure (MCP) by examining the monetary value of cocaine and alcohol in dual-dependent patients. Participants made hypothetical choices between pairs of substances and between each substance and a series of monetary values. Results showed that the combination of cocaine and alcohol was preferred over each individual substance. The monetary value at which the substance is no longer chosen was higher for the combination than for one drink or one hit alone. Monetary values showed convergence with dependence-related variables. These findings substantiate the importance of concurrent alcohol and cocaine dependence treatment.

Behavioral economic analysis of drug preference using multiple choice procedure data

The multiple choice procedure has been used to evaluate preference for psychoactive drugs, relative to money amounts (price), in human subjects. The present re-analysis shows that MCP data are compatible with behavioral economic analysis of drug choices. Demand curves were constructed from studies with intravenous fentanyl, intramuscular hydromorphone and oral methadone in opioid-dependent individuals; oral d-amphetamine, oral MDMA alone and during fluoxetine treatment, and smoked marijuana alone or following naltrexone pretreatment in recreational drug users. For each participant and dose, the MCP crossover point was converted into unit price (UP) by dividing the money value ($) by the drug dose (mg/70kg). At the crossover value, the dose ceases to function as a reinforcer, so "0" was entered for this and higher UPs to reflect lack of drug choice. At lower UPs, the dose functions as a reinforcer and "1" was entered to reflect drug choice. Data for UP vs. average percent choice were plotted in log-log space to generate demand functions. Rank of order of opioid inelasticity (slope of non-linear regression) was: fentanyl>hydromorphone (continuing heroin users)>methadone>hydromorphone (heroin abstainers). Rank order of psychostimulant inelasticity was d-amphetamine>MDMA>MDMA+fluoxetine. Smoked marijuana was more inelastic with high-dose naltrexone. These findings show this method translates individuals' drug preferences into estimates of population demand, which has the potential to yield insights into pharmacotherapy efficacy, abuse liability assessment, and individual differences in susceptibility to drug abuse.

Endogenous opiates and behavior: 2006

This paper is the 29th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning 30 years of research. It summarizes papers published during 2006 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurological disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).