Utilizing a Two-stage Design to Investigate the Safety and Potential Efficacy of Monthly Naltrexone Plus Once-daily Bupropion as a Treatment for Methamphetamine Use Disorder

Extended observation of reduced methamphetamine use with combined naltrexone plus bupropion in the ADAPT-2 trial

BACKGROUND AND AIMS

A 12-week placebo-controlled, sequential parallel Accelerated Development of Additive Pharmacotherapy Treatment for Methamphetamine Use Disorder (ADAPT-2) trial evaluated the effects of extended-release injectable naltrexone plus extended-release oral bupropion (NTX + BUPN) on methamphetamine (MA) use over two stages. This study reports on the previously unpublished stage 2 MA use in participants randomized at stage 1 to receive NTX + BUPN through both stages compared with those assigned to placebo.

DESIGN

This is a secondary analysis of the US National Institute on Drug Abuse (NIDA) ADAPT-2 network trial.

SETTING

The parent ADAPT-2 trial was carried out across multiple NIDA Clinical Trials Network (CTN) sites in the United States.

PARTICIPANTS

This analysis includes 403 people with MA use disorder who participated in the ADAPT-2 CTN trial.

INTERVENTION AND COMPARATOR

NTX + BUPN was compared with placebo over the course of the trial.

MEASUREMENT

MA use was measured by urine drug screens conducted twice weekly for 12 weeks, then once in week 13 and once in week 16 post-treatment follow-up.

FINDINGS

Participants on NTX + BUPN in stage 1 showed an additional 9.2% increase [95% confidence interval (CI), 0.09%-17.9%, P = 0.038] during stage 2 in their probability of testing negative for MA, with a total increase of 27.1% (95% CI, 13.2%-41.1%, P < 0.001) over the full 12 weeks of treatment. In contrast, participants on placebo in both stages increased in probability of testing MA-negative by a total of 11.4% (95% CI, 4.1%-18.6%, P = 0.002) over all 12 weeks. The 12-week increase among participants on NTX + BUPN was significantly greater-by 15.8% (95% CI, 4.5%-27.0%, P = 0.006)-than the increase among those on placebo.

CONCLUSION

For people with methamphetamine (MA) use disorder receiving treatment with extended-release injectable naltrexone plus extended-release oral bupropion (NTX + BUPN), continued treatment with NTX + BUPN after 6 weeks is associated with additional reductions in MA use up to 12 weeks.

The ASAM/AAAP Clinical Practice Guideline on the Management of Stimulant Use Disorder

The American Society of Addiction Medicine/American Academy of Addiction Psychiatry (ASAM/AAAP) Clinical Practice Guideline on the Management of Stimulant Use Disorder provides guidance on evidence-based strategies for the treatment of stimulant use disorders (StUDs), stimulant intoxication, and stimulant withdrawal, as well as secondary and tertiary prevention of harms associated with stimulant use. The Clinical Guideline Committee (CGC) comprised experts from ASAM and AAAP representing a range of clinical settings and patient populations. The guideline was developed following modified GRADE methodology. The process included a systematic literature review as well as several targeted supplemental searches. The CGC utilized Evidence to Decision tables to review available evidence and rate the strength of each recommendation. The clinical practice guideline was revised based on external stakeholder review. Key takeaways included: Contingency management represents the current standard of care for treatment of StUDs; Pharmacotherapies may be utilized off-label to treat StUDs; Acute stimulant intoxication can result in life-threatening complications that should be addressed in an appropriate level of care; Secondary and tertiary prevention strategies should be used to reduce harms related to risky stimulant use.

Integrative Pharmacology in the Treatment of Substance Use Disorders

The detrimental physical, mental, and socioeconomic effects of substance use disorders (SUDs) have been apparent to the medical community for decades. However, it has become increasingly urgent in recent years to develop novel pharmacotherapies to treat SUDs. Currently, practitioners typically rely on monotherapy. Monotherapy has been shown to be superior to no treatment at all for most substance classes. However, many randomized controlled trials (RCTs) have revealed that monotherapy leads to poorer outcomes when compared with combination treatment in all specialties of medicine. The results of RCTs suggest that monotherapy frequently fails since multiple dysregulated pathways, enzymes, neurotransmitters, and receptors are involved in the pathophysiology of SUDs. As such, research is urgently needed to determine how various neurobiological mechanisms can be targeted by novel combination treatments to create increasingly specific yet exceedingly comprehensive approaches to SUD treatment. This article aims to review the neurobiology that integrates many pathophysiologic mechanisms and discuss integrative pharmacology developments that may ultimately improve clinical outcomes for patients with SUDs. Many neurobiological mechanisms are known to be involved in SUDs including dopaminergic, nicotinic, N-methyl-D-aspartate (NMDA), and kynurenic acid (KYNA) mechanisms. Emerging evidence indicates that KYNA, a tryptophan metabolite, modulates all these major pathophysiologic mechanisms. Therefore, achieving KYNA homeostasis by harmonizing integrative pathophysiology and pharmacology could prove to be a better therapeutic approach for SUDs. We propose KYNA-NMDA-α7nAChRcentric pathophysiology, the "conductor of the orchestra," as a novel approach to treat many SUDs concurrently. KYNA-NMDA-α7nAChR pathophysiology may be the "command center" of neuropsychiatry. To date, extant RCTs have shown equivocal findings across comparison conditions, possibly because investigators targeted single pathophysiologic mechanisms, hit wrong targets in underlying pathophysiologic mechanisms, and tested inadequate monotherapy treatment. We provide examples of potential combination treatments that simultaneously target multiple pathophysiologic mechanisms in addition to KYNA. Kynurenine pathway metabolism demonstrates the greatest potential as a target for neuropsychiatric diseases. The investigational medications with the most evidence include memantine, galantamine, and N-acetylcysteine. Future RCTs are warranted with novel combination treatments for SUDs. Multicenter RCTs with integrative pharmacology offer a promising, potentially fruitful avenue to develop novel therapeutics for the treatment of SUDs.

Naltrexone plus bupropion reduces cigarette smoking in individuals with methamphetamine use disorder: A secondary analysis from the CTN ADAPT-2 trial

INTRODUCTION

Methamphetamine (MA) use is marked by high rates of comorbid tobacco smoking, which is associated with more severe drug use and worse clinical outcomes compared to single use of either drug. Research has shown the combination of naltrexone plus oral bupropion (NTX-BUP) improves smoking cessation outcomes in non-MA-using populations. In the Accelerated Development of Additive Pharmacotherapy Treatment (ADAPT-2) study, NTX-BUP successfully reduced MA use. Our aim in this secondary data analysis was to examine changes in cigarette smoking among the subgroup of participants reporting comorbid tobacco use in the ADAPT-2 trial.

METHODS

The multi-site ADAPT-2 study used a randomized, double blind, sequential parallel comparison design to evaluate treatment with extended-release injectable NTX (380 mg every 3 weeks) combined with once-daily oral extended-release BUP (450 mg/day) vs matching injectable and oral placebo in outpatients with moderate or severe MA use disorder. The study assessed smoking outcomes, based on self-reported timeline followback (TLFB) data, twice/week for 13 weeks.

RESULTS

Of the 403 participants in the ADAPT-2 trial, 290 reported being current cigarette smokers (71.9 %). The study found significant differences (p's < 0.0001) for each smoking outcome indicating greater change in the proportion of nonsmoking days, number of cigarettes smoked per week, and consecutive nonsmoking days, all favoring the group receiving NTX-BUP versus placebo.

CONCLUSIONS

NTX-BUP was associated with significant reductions in self-reported cigarette smoking in the context of concurrent treatment for MA use disorder. These off-target medication effects warrant prospective investigation using biochemically confirmed measures of smoking abstinence. The development of NTX-BUP as a co-addiction treatment strategy has a potential for high public health impact.

High suicidality predicts overdose events among people with substance use disorder: A latent class analysis

Introduction

Suicide is the tenth leading cause of death in the United States and continues to be a major public health concern. Suicide risk is highly prevalent among individuals with co-occurring substance use disorders (SUD) and mental health disorders, making them more prone to adverse substance use related outcomes including overdose. Identifying individuals with SUD who are suicidal, and therefore potentially most at risk of overdose, is an important step to address the synergistic epidemics of suicides and overdose fatalities in the United States. The current study assesses whether patterns of suicidality endorsement can indicate risk for substance use and overdose.

Methods

Latent class analysis (LCA) was used to assess patterns of item level responses to the Concise Health Risk Tracking Self-Report (CHRT-SR), which measures thoughts and feelings associated with suicidal propensity. We used data from 2,541 participants with SUD who were enrolled across 8 randomized clinical trials in the National Drug Abuse Treatment Clinical Trials Network from 2012 to 2021. Characteristics of individuals in each class were assessed, and multivariable logistic regression was performed to examine class membership as a predictor of overdose. LCA was also used to analyze predictors of substance use days.

Results

Three classes were identified and discussed: Class (1) Minimal Suicidality, with low probabilities of endorsing each CHRT-SR construct; Class (2) Moderate Suicidality, with high probabilities of endorsing pessimism, helplessness, and lack of social support, but minimal endorsement of despair or suicidal thoughts; and Class (3) High Suicidality with high probabilities of endorsing all constructs. Individuals in the High Suicidality class comprise the highest proportions of males, Black/African American individuals, and those with a psychiatric history and baseline depression, as compared with the other two classes. Regression analysis revealed that those in the High Suicidality class are more likely to overdose as compared to those in the Minimal Suicidality class (p = 0.04).

Conclusion

Suicidality is an essential factor to consider when building strategies to screen, identify, and address individuals at risk for overdose. The integration of detailed suicide assessment and suicide risk reduction is a potential solution to help prevent suicide and overdose among people with SUD.

Suicidality as a Predictor of Overdose among Patients with Substance Use Disorders

Increasing rates of overdose and overdose deaths are a significant public health problem. Research has examined co-occurring mental health conditions, including suicidality, as a risk factor for intentional and unintentional overdose among individuals with substance use disorder (SUD). However, this research has been limited to single site studies of self-reported outcomes. The current research evaluated suicidality as a predictor of overdose events in 2541 participants who use substances enrolled across eight multi-site clinical trials completed within the National Drug Abuse Treatment Clinical Trials Network between 2012 to 2021. The trials assessed baseline suicidality with the Concise Health Risk Tracking Self-Report (CHRT-SR). Overdose events were determined by reports of adverse events, cause of death, or hospitalization due to substance overdose, and verified through a rigorous adjudication process. Multivariate logistic regression was performed to assess continuous CHRT-SR score as a predictor of overdose, controlling for covariates. CHRT-SR score was associated with overdose events (p = 0.03) during the trial; the likelihood of overdose increased as continuous CHRT score increased (OR 1.02). Participants with lifetime heroin use were more likely to overdose (OR 3.08). Response to the marked rise in overdose deaths should integrate suicide risk reduction as part of prevention strategies.

Bupropion and Naltrexone in Methamphetamine Use Disorder

BACKGROUND

The use of naltrexone plus bupropion to treat methamphetamine use disorder has not been well studied.

METHODS

We conducted this multisite, double-blind, two-stage, placebo-controlled trial with the use of a sequential parallel comparison design to evaluate the efficacy and safety of extended-release injectable naltrexone (380 mg every 3 weeks) plus oral extended-release bupropion (450 mg per day) in adults with moderate or severe methamphetamine use disorder. In the first stage of the trial, participants were randomly assigned in a 0.26:0.74 ratio to receive naltrexone-bupropion or matching injectable and oral placebo for 6 weeks. Those in the placebo group who did not have a response in stage 1 underwent rerandomization in stage 2 and were assigned in a 1:1 ratio to receive naltrexone-bupropion or placebo for an additional 6 weeks. Urine samples were obtained from participants twice weekly. The primary outcome was a response, defined as at least three methamphetamine-negative urine samples out of four samples obtained at the end of stage 1 or stage 2, and the weighted average of the responses in the two stages is reported. The treatment effect was defined as the between-group difference in the overall weighted responses.

RESULTS

A total of 403 participants were enrolled in stage 1, and 225 in stage 2. In the first stage, 18 of 109 participants (16.5%) in the naltrexone-bupropion group and 10 of 294 (3.4%) in the placebo group had a response. In the second stage, 13 of 114 (11.4%) in the naltrexone-bupropion group and 2 of 111 (1.8%) in the placebo group had a response. The weighted average response across the two stages was 13.6% with naltrexone-bupropion and 2.5% with placebo, for an overall treatment effect of 11.1 percentage points (Wald z-test statistic, 4.53; P<0.001). Adverse events with naltrexone-bupropion included gastrointestinal disorders, tremor, malaise, hyperhidrosis, and anorexia. Serious adverse events occurred in 8 of 223 participants (3.6%) who received naltrexone-bupropion during the trial.

CONCLUSIONS

Among adults with methamphetamine use disorder, the response over a period of 12 weeks among participants who received extended-release injectable naltrexone plus oral extended-release bupropion was low but was higher than that among participants who received placebo. (Funded by the National Institute on Drug Abuse and others; ADAPT-2 ClinicalTrials.gov number, NCT03078075.).

Medication Adherence Monitoring Using Smartphone Video Dosing in an Open-label Pilot Study of Monthly Naltrexone Plus Once-daily Bupropion for Methamphetamine Use Disorder: Feasibility and Acceptability

OBJECTIVES

This article describes how smartphones were used to monitor and encourage medication adherence in a pilot study evaluating the potential efficacy of a combination pharmacotherapy for methamphetamine use disorder. We examine the feasibility, utility, and acceptability of using smartphones to capture dosing videos from the perspectives of participants and staff.

METHODS

The study was an 8-week, open-label evaluation of extended-release injectable naltrexone combined with once-daily oral extended-release bupropion (BRP, Welbutrin XL, 450 mg/day). Participants attended visits twice-weekly for observed BRP dosing, assessments, and medical management. BRP was dispensed once weekly for dosing on nonclinic days. Medication adherence was assessed objectively (by observation in the clinic and smartphone videos for dosing at home) and subjectively (self-reports of dosing). Surveys assessing the smartphone component were completed by participants and study staff.

RESULTS

Participants (N = 49) reported taking 93.6% of the dispensed BRP doses while 86.6% of dispensed doses were confirmed via dosing video and in-person observations. Most participants who completed the survey agreed that the smartphone was easy to use (92.6%) and that taking the dosing videos helped to remember to take the study medication (80.5%). Staff agreed that the smartphone helped collect accurate dosing data for most (77.5%) participants.

CONCLUSIONS

The use of smartphones for video-based oral medication dosing in this study provided a feasible and acceptable mechanism to encourage, monitor, and confirm medication adherence. Video-confirmed dosing adherence provides an objective numerical indicator of the lowest medication adherence rate participants achieve, allowing investigators to more confidently interpret results.

Endogenous opiates and behavior: 2017

This paper is the fortieth consecutive installment of the annual anthological review of research concerning the endogenous opioid system, summarizing articles published during 2017 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides and receptors as well as effects of opioid/opiate agonists and antagonists. The review is subdivided into the following specific topics: molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors (1), the roles of these opioid peptides and receptors in pain and analgesia in animals (2) and humans (3), opioid-sensitive and opioid-insensitive effects of nonopioid analgesics (4), opioid peptide and receptor involvement in tolerance and dependence (5), stress and social status (6), learning and memory (7), eating and drinking (8), drug abuse and alcohol (9), sexual activity and hormones, pregnancy, development and endocrinology (10), mental illness and mood (11), seizures and neurologic disorders (12), electrical-related activity and neurophysiology (13), general activity and locomotion (14), gastrointestinal, renal and hepatic functions (15), cardiovascular responses (16), respiration and thermoregulation (17), and immunological responses (18).

Responding to global stimulant use: challenges and opportunities

We did a global review to synthesise data on the prevalence, harms, and interventions for stimulant use, focusing specifically on the use of cocaine and amphetamines. Modelling estimated the effect of cocaine and amphetamine use on mortality, suicidality, and blood borne virus incidence. The estimated global prevalence of cocaine use was 0·4% and amphetamine use was 0·7%, with dependence affecting 16% of people who used cocaine and 11% of those who used amphetamine. Stimulant use was associated with elevated mortality, increased incidence of HIV and hepatitis C infection, poor mental health (suicidality, psychosis, depression, and violence), and increased risk of cardiovascular events. No effective pharmacotherapies are available that reduce stimulant use, and the available psychosocial interventions (except for contingency management) had a weak overall effect. Generic approaches can address mental health and blood borne virus infection risk if better tailored to mitigate the harms associated with stimulant use. Substantial and sustained investment is needed to develop more effective interventions to reduce stimulant use.

Gaps in the ice: Methamphetamine in Australia; its history, treatment, and ramifications for users and their families

It is now well-established that Australia has a significant issue with methamphetamine. Recent dramatic changes in manufacturing have led to significant shifts in both the patterns of use and the relative purity of this illicit drug, with the crystalline form of methamphetamine commonly referred to as 'ice'. Excessive use not only impacts on those taking the drug, but also takes a heavy toll on their families. With few effective treatment options currently available, there is a strong focus on developing replacement pharmacotherapies and examining the efficacy of outpatient counselling and residential treatment options. Recent research in addiction care supports the positive impact that families of users can have on both treatment and recovery for their loved ones. Despite this recognition, there is little current research looking at the experiences of families of users of the uniquely problematic drug methamphetamine. This paper outlines the historical narrative that has led to the current worldwide phenomenon of ice use and explores contemporary directions of research into its impact and potential treatments. In doing so, it outlines the relatively unexplored impact of ice on families and highlights a current need for nursing research into their experiences living with loved ones using the drug.

Efficacy and safety of naltrexone for amfetamine and methamfetamine use disorder: a systematic review of randomized controlled trials

INTRODUCTION

Amfetamine and methamfetamine abuse remains a prevalent health problem, increasing the burden on healthcare. Naltrexone, a µ-opioid receptor antagonist, has been suggested as a promising treatment for amfetamine and methamfetamine use disorder.

OBJECTIVE

To review the current evidence for the efficacy and safety of naltrexone as a pharmacological treatment for amfetamine and methamfetamine use disorder. The primary outcome was defined as abstinence or reduction of use. Secondary outcomes were, attenuated "positive" subjective effects (e.g., "feel good," "craving," etc.) of amfetamine or methamfetamine after naltrexone treatment, adverse events and physiological changes (e.g., blood pressure, heart rate).

METHODS

This systematic review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. A systematic literature search was conducted on 2 April 2017, and updated on 31 March 2018. Records were retrieved from databases including PubMed, EMBASE Classic plus EMBASE 1980 via Ovid, and the databases were searched using keywords and/or headings: (naltrexone AND amfetamine AND dependence) OR (naltrexone AND amfetamine AND craving) OR (vivitrol AND amfetamine) OR (revia AND amfetamine) OR (naltrexone AND amfetamine) OR (naltrexone AND methamfetamine dependence) OR (naltrexone AND methamfetamine AND craving) OR (vivitrol AND methamfetamine) OR (revia AND methamfetamine) OR (naltrexone AND ice) OR (naltrexone AND crystal meth) OR (naltrexone AND methamfetamine). Studies investigating the effects of naltrexone on amfetamine or methamfetamine use were eligible for inclusion. All studies were rated as low risk of bias using the Cochrane tool for risk of bias.

RESULTS

Among 591 identified studies, there were four randomized controlled trials. Two studies investigated the effects of naltrexone on amfetamine use disorder and two on methamfetamine use. Compared to placebo, the abstinence rate was increased significantly (p < 0.05) by naltrexone in one of two amfetamine studies, whereas there was no statistical difference in the only study reporting methamfetamine use. In one out of two amfetamine studies, naltrexone significantly attenuated either craving levels or subjective effects (e.g., "want more," "like effect") relative to placebo (p < 0.05). Additionally, only in one of two methamfetamine studies did naltrexone produce a significant reduction (p < 0.05) in craving levels or attenuated subjective effects. Both amfetamine and methamfetamine studies showed good tolerability of naltrexone, with few adverse events seen.

CONCLUSIONS

There is presently insufficient evidence to support the use of naltrexone in amfetamine and metamfetamine use disorders. There is a compelling need for high-quality studies to further evaluate the potential use of naltrexone.

Pharmacotherapy for amphetamine dependence: A systematic review

BACKGROUND

Demand for treatment for amphetamine use is increasing internationally. Establishing effective pharmacotherapy provides broader treatment options for people who are dependent on amphetamine and may encourage engagement in evidence-based behavioral treatment. This study aimed to identify medicines that have potential in improving treatment outcomes for people who are dependent on amphetamines.

METHODS

Medline, PsycINFO, Embase and the Cochrane Database of Systematic Reviews were searched from 1997 to 2012 and again from 2013 to 2016. Studies on medications for amphetamine/methamphetamine dependence treatment were selected and assessed by two independent researchers. A meta-narrative review approach was used to synthesize results.

RESULTS

A total of 49 studies investigating 20 potential pharmacotherapies were eligible for inclusion. Of these, 35 studies related to 33 level II quality randomized controlled trials (RCTs). Five medications were subject to multiple RCTs. Four of these medicines demonstrated some limited evidence of benefit for reducing amphetamine use: methylphenidate (as reported in three studies), bupropion (in three studies), modafinil (two studies), and naltrexone (one study). Four RCTs of dexamphetamine suggest its benefit on secondary outcomes such as treatment retention, but not for reducing amphetamine use. Six other medicines indicate the potential for efficacy, but the number of studies is too small to draw conclusions.

CONCLUSIONS

No medicine has as yet demonstrated sufficient, consistent evidence of effectiveness to support its use in routine treatment. High study drop-out and poor medication adherence limits the strength of evidence and raises important clinical questions about how to improve treatment engagement and outcomes.

Extended-release naltrexone for methamphetamine dependence among men who have sex with men: a randomized placebo-controlled trial

BACKGROUND AND AIMS

Methamphetamine use is increasingly prevalent and associated with HIV transmission. Early-phase human studies suggested naltrexone reduced amphetamine use among dependent individuals. We tested if extended-release naltrexone (XRNTX) reduces methamphetamine use and associated sexual risk behaviors among high-risk methamphetamine-dependent men who have sex with men (MSM).

DESIGN

Double-blind, placebo-controlled, randomized trial of XRTNX versus placebo over 12 weeks from 2012 to 2015.

SETTING

San Francisco Department of Public Health, California, USA.

PARTICIPANTS

One hundred community-recruited, sexually-active, actively-using methamphetamine-dependent MSM. Mean age was 43.2 years; 96% were male, 3% transfemale, and 1% transmale; 55.0% were white, 19.0% African American, and 18.0% Latino.

INTERVENTIONS

XRNTX 380 mg (n = 50) or matched placebo (n = 50) administered by gluteal injection at 4-week intervals.

MEASUREMENTS

Regression estimated average level and change in level of positive urines during the period 2-12 weeks (primary outcomes) and sexual risk behaviors (secondary outcome).

FINDINGS

Ninety per cent of visits were completed. By intent-to-treat, participants assigned to XRNTX had similar differences during 2-12 weeks in methamphetamine-positive urines as participants assigned to placebo [incidence rate ratio (IRR) = 0.95, 95% confidence interval (CI) = 0.76-1.20; Bayes factor < 0.3]. Observed urine positivity declined from 78 to 70% in the XRNTX arm and 74 to 64% in the placebo arm. Adherence to injections was 96.7% in the XRNTX arm and 91.3% in the placebo arm. Sexual risk behaviors declined similarly among participants in both arms (all P > 0.05). There were no serious adverse events related to study drug and no differences in frequency of adverse events by treatment arm.

CONCLUSIONS

Notwithstanding very high medication adherence for this study, extended-release naltrexone does not appear to reduce methamphetamine use or sexual risk behaviors among methamphetamine-dependent men who have sex with men compared with placebo.

Medications for substance use disorders (SUD): emerging approaches

INTRODUCTION

Substance use disorders are a group of chronic relapsing disorders of the brain, which have massive public health and societal impact. In some disorders (e.g., heroin/prescription opioid addictions) approved medications have a major long-term benefit. For other substances (e.g., cocaine, amphetamines and cannabis) there are no approved medications, and for alcohol there are approved treatments, which are not in wide usage. Approved treatments for tobacco use disorders are available, and novel medications are also under study. Areas covered: Medication-based approaches which are in advanced preclinical stages, or which have reached proof-of concept clinical laboratory studies, as well as clinical trials. Expert opinion: Current challenges involve optimizing translation between preclinical and clinical development, and between clinical laboratory studies to therapeutic clinical trials. Comorbidities including depression or anxiety are challenges for study design and analysis. Improved pharmacogenomics, biomarker and phenotyping approaches are areas of interest. Pharmacological mechanisms currently under investigation include modulation of glutamatergic, GABA, vasopressin and κ-receptor function, as well as inhibition of monoamine re-uptake. Other factors that affect potential market size for emerging medications include stigma, availability of treatment settings, adoption by clinicians, and the prevalence of persons with SUD who are not actively treatment-seeking.