Opioid addiction: Who are your real friends?

Substance Use Among Residents of Homeless Shelters During the COVID-19 Pandemic: Findings From France

Objectives: To record the prevalence and risk factors of substance use amongst homeless persons during the COVID-19 pandemic.

Methods: The ECHO study consisted in two independent cross-sectional waves of data collection in the regions of Paris, Lyon, and Strasbourg during the Spring of 2020 (n = 530) and 2021 (n = 319). Factors associated with substance use were explored using generalised logistic regression models.

Results: The most prevalent substance used was tobacco (38%–43%), followed by alcohol (26%–34%). The use of both substances positively associated with each other, although risk factors varied depending on the substance. The only factors consistently associated with alcohol and tobacco use were being male, exposure to theft/assault and participants’ region of origin. Whilst the rate of tobacco use was relatively stable between Spring 2020 and 2021, alcohol use was more common in 2021.

Conclusion: These findings highlight a high prevalence of substance use amongst homeless persons. People experiencing homelessness face specific challenges in the context of the pandemic, alongside greater vulnerability to illness and low healthcare access, therefore the need to improve prevention and support services for substance abuse within this population is vital.

Novel digital approaches to the assessment of problematic opioid use

The opioid epidemic continues to contribute to loss of life through overdose and significant social and economic burdens. Many individuals who develop problematic opioid use (POU) do so after being exposed to prescribed opioid analgesics. Therefore, it is important to accurately identify and classify risk factors for POU. In this review, we discuss the etiology of POU and highlight novel approaches to identifying its risk factors. These approaches include the application of polygenic risk scores (PRS) and diverse machine learning (ML) algorithms used in tandem with data from electronic health records (EHR), clinical notes, patient demographics, and digital footprints. The implementation and synergy of these types of data and approaches can greatly assist in reducing the incidence of POU and opioid-related mortality by increasing the knowledge base of patient-related risk factors, which can help to improve prescribing practices for opioid analgesics.

Deep Brain Stimulation in Drug Addiction Treatment: Research Progress and Perspective

Drug addiction is a chronic psychiatric disorder characterized by compulsive drug-seeking and drug-using behavior, and a tremendous socioeconomic burden to society. Current pharmacological and psychosocial methods have shown limited treatment effects for substance abuse. Deep Brain Stimulation (DBS) is a novel treatment for psychiatric disease and has gradually gained popularity in the treatment of addiction. Addiction is characterized by neuroplastic changes in the nucleus accumbens (NAc), a key structure in the brain reward system, and DBS in this region has shown promising treatment effects. In this paper, the research progress on DBS for drug addiction has been reviewed. Specifically, we discuss the mechanism of NAc DBS for addiction treatment and summarize the results of clinical trials on DBS treatment for addiction to psychoactive substances such as nicotine, alcohol, cocaine, opioids and methamphetamine/amphetamine. In addition, the treatment effects of DBS in other brain regions, such as the substantia nigra pars reticulata (SNr) and insula are discussed.

The Association of Drug-Use Characteristics and Active Coping Styles With Positive Affect in Patients With Heroin-Use Disorder and Methamphetamine-Use Disorder During the COVID-19 Pandemic

Background: Positive affect (PA) is crucial for individuals to cope with the current pandemic and buffer the lingering fears after it, especially for patients with substance-use disorders (SUDs). The current study aimed to explore PA and its related factors during the COVID-19 pandemic in male patients with the heroin-use disorder (HUD) and patients with the methamphetamine-use disorder (MAUD), respectively.

Methods: A total of 325 male patients with SUDs (106 with HUD and 219 with MAUD, all were single-substance users) in a compulsory rehabilitation center underwent semi-structured interviews during the pandemic. The demographic information, drug-use characteristics, active coping styles (ACSs, by Simple Coping Style Questionnaire), and PA (by the Positive and Negative Affect Scale) of participants were collected and recorded.

Results: There were significant differences between the two groups in age, the proportion of full-time workers before the epidemic, duration of drug use, the proportion of patients with long-term withdrawal during the epidemic, cravings, ACS, and PA. Correlation and multiple linear regression analysis showed that duration of drug use, ACS, and stable jobs were significant predictive factors for PA in patients with HUD, while long-term withdrawal, ACS, and stable jobs during the epidemic were significant predictive factors for PA in patients with MAUD.

Conclusions: Our study demonstrated the factors for PA in patients with HUD and MAUD during the pandemic. The results provided a basis for the comprehensive understanding of the PA of patients with SUDs and the development of targeted treatments.

Mini-review: A possible role for galanin in post-traumatic stress disorder

Several neuroendocrine systems have been implicated in post-traumatic stress disorder, including the mesocortical and mesolimbic dopamine, the norepinephrine, the β-endorphin, the serotonin, and the oxytocin systems. The interaction between these different systems remains, however, largely unknown and a generally accepted unifying theory is thus far lacking. In this review, we suggest that galanergic suppression of dopaminergic neurons in the ventral tegmental may constitute the missing link in a post-traumatic feedback loop. In addition, we address the literature on the negative cross-antagonism in this brain region between the galanin 1 and μ-opioid receptors, which suggests that behavioural patterns which stimulate β-endorphin, a natural μ-opioid receptors ligand, secretion may provide novel avenues for the treatment and prevention of PTSD, as well as for recruitment, training, and leadership processes in high-stress/high-risk professions such as the military, first responders and the police.

Addressing opioid tolerance and opioid-induced hypersensitivity: Recent developments and future therapeutic strategies

Opioids are a commonly prescribed and efficacious medication for the treatment of chronic pain but major side effects such as addiction, respiratory depression, analgesic tolerance, and paradoxical pain hypersensitivity make them inadequate and unsafe for patients requiring long-term pain management. This review summarizes recent advances in our understanding of the outcomes of chronic opioid administration to lay the foundation for the development of novel pharmacological strategies that attenuate opioid tolerance and hypersensitivity; the two main physiological mechanisms underlying the inadequacies of current therapeutic strategies. We also explore mechanistic similarities between the development of neuropathic pain states, opioid tolerance, and hypersensitivity which may explain opioids' lack of efficacy in certain patients. The findings challenge the current direction of analgesic research in developing non-opioid alternatives and we suggest that improving opioids, rather than replacing them, will be a fruitful avenue for future research.

Socially-supportive norms and mutual aid of people who use opioids: An analysis of Reddit during the initial COVID-19 pandemic

BACKGROUND

Big events (i.e., unique historical disruptions) like the COVID-19 epidemic and its associated period of social distancing can transform social structures, social interactions, and social norms. Social distancing rules and the fear of infection have greatly reduced face-to-face interactions, increased loneliness, reduced ties to helping institutions, and may also have disrupted the opioid use behaviors of people who use drugs. This research used Reddit to examine the impact of COVID-19 on the social networks and social processes of people who use opioids.

METHODS

Data were collected from the social media forum, Reddit.com. At the beginning of the COVID-19 pandemic in the U.S. (March 5, 2020, to May 13, 2020), 2,000 Reddit posts were collected from the two most popular opioid subreddits (r/OpiatesRecovery, r/Opiates). Posts were reviewed for relevance to COVID-19 and opioid use resulting in a final sample of 300. Thematic analysis was guided by the Big Events framework.

RESULTS

The COVID-19 pandemic was found to create changes in the social networks and daily lives among persons who use opioids. Adaptions to these changes shifted social networks leading to robust social support and mutual aid on Reddit, including sharing and seeking advice on facing withdrawal, dealing with isolation, managing cravings, and accessing recovery resources.

CONCLUSIONS

Reddit provided an important source of social support and mutual aid for persons who use opioids. Findings indicate online social support networks are beneficial to persons who use opioids, particularly during big events where isolation from other social support resources may occur.

The self-serving benefits of being a good host: A role for our micro-inhabitants in shaping opioids' function

Opioids are highly efficacious in their ability to relieve pain, but they are liable for abuse, dependence, and addiction. Risk factors to develop opioid use disorders (OUD) include chronic stress, socio-environment, and preexisting major depressive disorders (MDD) and posttraumatic stress disorders (PTSD). Additionally, opioids reduce gut motility, induce loss of gut barrier function, and alter the composition of the trillions of microbes hosted in the gastrointestinal tract, known as the gut microbiota. The microbiota are significant contributors to the reciprocal communication between the central nervous system (CNS) and the gut, termed the gut-brain axis. They have strong influences on their host behaviors, including the ability to cope with stress, sociability, affect, mood, and anxiety. Thus, they are implicated in the etiology of MDD and PTSD. Here we review the latest studies demonstrating that intestinal flora can, directly and indirectly, by affecting sociability levels, responses to stress, and mental state, alter the responses to opioids. It suggests that microbiota can potentially be used to increase the resilience to develop analgesic tolerance and OUD.

The prospective association between illicit drug use and nonprescription opioid use among vulnerable adolescents

In recent years, more than half of all drug overdose deaths in United States involved an opioid. To address this epidemic, antecedents to opioid misuse must be identified and empirically validated. The objective of the current investigation was to examine whether illicit drug use was prospectively associated with nonprescription opioid use among adolescents from a vulnerable population with a greater prevalence of substance abuse. A population-based cohort study of 1060 adolescents from 29 alternative high schools in southern California was conducted over a two-year period. A total of 929 adolescents (mean age 17.5 years, 49.9% female, 76.4% Hispanic) who had not experimented with nonprescription opioids at the baseline assessment were included in the analytic sample. The outcome was self-reported use of nonprescription opioids within two years. The predictors tested were illicit drug use, illicit drug use excluding marijuana, and the use of nonmedical marijuana. Covariates included age, sex, ethnicity, socioeconomic status, parental education, weekly income, sensation seeking, stress, anxiety, depression, and the use of alcohol and nicotine products. Multilevel, covariate-adjusted logistic regression models indicated that the odds of experimentation with nonprescription opioids was greater among adolescents who had used illicit drugs or illicit drugs excluding marijuana. Nonmedical marijuana use alone was a statistically significant predictor in unadjusted but not covariate-adjusted models. While prior studies have examined the progression from nicotine, alcohol, and marijuana use to nonprescription opioid use, the present findings emphasize the importance of illicit drug use as a detectable and empirically supported risk factor for future opioid misuse.

NPY alterations induced by chronic morphine exposure affect the maintenance and reinstatement of morphine conditioned place preference

Opioid addiction is a brain disease that severely harms society and personal health. Although the tremendous numbers of patients worldwide and emerged negative events, effective treatments for opioid addiction are still lacking. Neuropeptide Y (NPY) is one of the main orexigenic peptides that play vital roles in food intake and energy metabolism. However, increasing evidence indicates that NPY may have great potential in mediating reward effects and drug dependence. In the present study, we assessed the expression changes of NPY in the nucleus accumbens at different timepoints following morphine conditioned place preference (CPP) and investigated the functional importance of potential NPY changes. Our results showed that NPY expression significantly decreased in the nucleus accumbens shell (AcbSh) immediately after chronic morphine exposure. Subsequently, it increased rapidly at first and then gradually returned to normal levels. Further data indicated that these NPY changes were involved in morphine reward memory, demonstrated by a reduction in the extinction period after blocking of the Y5 receptor by L-152,804 in the AcbSh and a prolonged duration of the extinction period following the application of NPY. More importantly, the additional results revealed that L-152,804 also remarkably suppressed the reinstatement of morphine CPP. Together, our results indicate that a complicated plasticity of the NPY pathway in AcbSh occurs following morphine CPP, and this plasticity plays an important role in modulating morphine reward memory. These findings may enhance our understanding of the role of the NPY system in opioid addiction and indicate a promising target for opioid addiction treatment.

Effect of Ego Depletion on Interpersonal Trust among Individuals with Substance Use Disorders

Individuals with substance use disorders (SUD) undergo treatment to recover from addiction. However, exerting self-control, which is essential for successful abstinence from drug addiction, can cause ego depletion. This study experimentally investigated the effect of ego depletion on interpersonal trust and examined possible changes in the ego depletion effect across different abstinence periods. This study employed a 2 (ego depletion: high vs. low) × 2 (partners: non-SUD vs. SUD) mixed factorial design. The participants were 273 male individuals with SUD and with periods of drug abstinence ranging from several days to 2 years, who resided in a compulsory drug rehabilitation center. The participants were first asked to complete an ego depletion task, followed by a decision-making task in a trust game, first with a non-SUD stranger, and then with a SUD stranger. Ego depletion was not related to trust in non-SUD strangers. However, ego depleted participants were more likely to trust SUD strangers than non-ego depleted participants. Moreover, this ego depletion effect fluctuated near the end of SUD treatment. This study highlights the importance to ensure follow-up outpatient care and offer social support services for individuals with SUD after compulsory SUD treatment.

Spatial heterogeneity and socioeconomic determinants of opioid prescribing in England between 2015 and 2018

BACKGROUND

Opioid overdoses have had a serious impact on the public health systems and socioeconomic welfare of several countries. Within this broader context, we focus our study on primary care opioid prescribing in England from 2015 to 2018, particularly the patterns of spatial variations at the community level and the socioeconomic and environmental factors that drive consumption.

METHODS

Leveraging open data sources, we combine prescription records with aggregated data on patient provenance and build highly granular maps of Oral Morphine Equivalent (OME) prescribing rates for Lower Layer Super Output Areas (LSOA). We quantify the strength of spatial associations by means of the Empirical Bayes Index (EBI) that accounts for geographical variations in population density. We explore the interplay between socioeconomic and environmental determinants and prescribing rates by implementing a multivariate logistic regression model across different temporal snapshots and spatial scales.

RESULTS

We observe, across time and geographical resolutions, a significant spatial association with the presence of localized hot and cold spots that group neighboring areas with homogeneous prescribing rates (e.g., EBI = 0.727 at LSOA level for 2018). Accounting for spatial dependency effects, we find that LSOA with both higher employment deprivation (OR = 62.6, CI 52.8-74.3) and a higher percentage of ethnically white (OR = 30.1, CI 25.4-35.7) inhabitants correspond to higher prescribing rates. Looking at educational attainment, we find LSOA with the prevalent degree of education being apprenticeship (OR = 2.33, CI 1.96-2.76) a risk factor and those with level 4+ (OR = 0.41, CI 0.35-0.48) a protective factor. Focusing on environmental determinants, housing (OR = 0.18, CI 0.15-0.21) and outdoor environment deprivation (OR = 0.62, CI 0.53-0.72) indices capture the bi-modal behavior observed in the literature concerning rural/urban areas. The results are consistent across time and spatial aggregations.

CONCLUSIONS

Failing to account for local variations in opioid prescribing rates smooths out spatial dependency effects that result in underestimating/overestimating the impact on public health policies at the community level. Our study suggests a novel approach to inform more targeted interventions toward the most vulnerable population strata.

The Psychiatric Characteristics of People on a Mephedrone ("bath salts") Binge

Background: Despite solutions presented by the European Union and national regulations introduced by many countries, the problem of mephedrone (4-MMC) is growing. Objectives: The aim of this study was to investigate the effect of regular mephedrone intake with other psychoactive substances on the clinical picture of patients, including self-harms and suicide attempts. Methods: The study involved a group of 601 patients addicted to mephedrone who were admitted to a psychiatric hospital between 2010 and 2018 due to regular mephedrone intake. Results: There was a statistically significant relationship between sleep disorders and mephedrone combined with alcohol (p < .05) or cannabinols (p < .05). However, the highest number of statistically significant correlations was reported when mephedrone was combined with opioids. There was a growing year-on-year percentage of people who attempted suicide because of regular mephedrone intake (p < .001). The more psychoactive substances were combined with mephedrone, the greater the risk of attempted suicide (p < .01). 20% of the examined group were hospitalized several times. Among those hospitalized several times, significantly more people took more than one additional psychoactive substance (p < .01). Conclusions: The more psychoactive substances combined with mephedrone, the more clinical symptoms are associated with it.

Stigma Associated with Opioid Use Disorders in Adolescents Limits Naloxone Prescribing

THEORETICAL PRINCIPLES

Parse's theory of humanbecoming describes shame as a sense that one is failing to conform to both personal and societal expectations of high value. Shame and stigma, negative perceptions others hold of an individual based on failure to conform to societal expectations, that surround opioid use disorders are linked to patients not seeking medical treatment due to the social isolation and humiliation brought on by the disease.

PHENOMENON ADDRESSED

This article reviews the resistance of some health care providers to discuss the realities of substance abuse with adolescent patients and their families, and identifies how the stigma that some health care providers place on opioid use disorders makes them less likely to discuss and prescribe naloxone, the reversal agent for opioids. When families are prepared to prevent overdose deaths by administering naloxone, lives can be saved, and time can be preserved for developing long-term treatment options.

RESEARCH LINKAGES

Research should develop curricula that teach how to identify unconscious bias that may exist on the part of the healthcare provider, and to understand the negative effects of stigmatizing opioid use. Bedside nurses and practitioners should be equipped to educate patients and their families about naloxone and its availability, and to explain that it is a safe and effective way to prevent opioid related deaths. When presented in a nonjudgmental way, information about naloxone is a critical component in addressing the opioid epidemic, preventing deaths and providing time for further treatment options.

A Biopsychosocial Overview of the Opioid Crisis: Considering Nutrition and Gastrointestinal Health

The opioid crisis has reached epidemic proportions in the United States with rising overdose death rates. Identifying the underlying factors that contribute to addiction vulnerability may lead to more effective prevention strategies. Supply side environmental factors are a major contributing component. Psychosocial factors such as stress, trauma, and adverse childhood experiences have been linked to emotional pain leading to self-medication. Genetic and epigenetic factors associated with brain reward pathways and impulsivity are known predictors of addiction vulnerability. This review attempts to present a biopsychosocial approach that connects various social and biological theories related to the addiction crisis. The emerging role of nutrition therapy with an emphasis on gastrointestinal health in the treatment of opioid use disorder is presented. The biopsychosocial model integrates concepts from several disciplines, emphasizing multicausality rather than a reductionist approach. Potential solutions at multiple levels are presented, considering individual as well as population health. This single cohesive framework is based on the interdependency of the entire system, identifying risk and protective factors that may influence substance-seeking behavior. Nutrition should be included as one facet of a multidisciplinary approach toward improved recovery outcomes. Cross-disciplinary collaborative efforts, new ideas, and fiscal resources will be critical to address the epidemic.

Trends of Opioid Use Disorder Among Hospitalized Patients With Chronic Pain

BACKGROUND

Patients with chronic pain treated with opioids are at an increased risk for opioid misuse or opioid use disorder (OUD). Recent years have seen a stark increase in abuse, misuse, and diversion of prescription opioid medications. The aim of this study was to investigate trends in changing rates of opioid use disorder among patients with chronic pain.

METHODS

The National Inpatient Sample (NIS) database identified chronic pain admissions with OUD from 2011 to 2015. Patients were identified from the NIS database using International Classification of Diseases (9th and 10th revisions) diagnosis codes for chronic pain and OUD. Annual estimates and trends were determined for OUD, patient characteristics, OUD among subgroups of chronic pain conditions, and discharge diagnosis.

RESULTS

We identified 10.3 million patients with chronic pain. Of these, 680,631 patients were diagnosed with OUD. The number of patients with OUD increased from 109,222 in 2011 to 172,680 in 2015 (P < 0.001). Similarly, there were upward trends of OUD among females (53.2% to 54.5%; P = 0.09), patients 65 to 84 years of age (11.8% to 17%; P < 0.001), Medicare-insured patients (39.5% to 46.0%; P < 0.01), patients with low annual household incomes (27.8% to 33.3%; P < 0.001), and patients with cannabinoid use disorder (7.2% to 8.3%; P = 0.01). The prevalence of OUD increased from 2011 to 2015 in patients with chronic regional pain syndrome (5.53% to 7.46%; P = 0.01) and spondylosis (1.32% to 1.81%; P < 0.001).

CONCLUSIONS

These findings suggest that the prevalence of OUD increased substantially from 2011 to 2015. Disparities of OUD with increasing opioid use among vulnerable populations including women, those with Medicare insurance, tobacco use disorder, and low annual income should be explored further.

Stress, sensitive periods, and substance abuse

Research on the inter-relationship between drug abuse and social stress has primarily focused on the role of stress exposure during adulthood and more recently, adolescence. Adolescence is a time of heightened reward sensitivity, but it is also a time when earlier life experiences are expressed. Exposure to stress early in postnatal life is associated with an accelerated age of onset for drug use. Lifelong addiction is significantly greater if drug use is initiated during early adolescence. Understanding how developmental changes following stress exposure interact with sensitive periods to unfold over the course of maturation is integral to reducing their later impact on substance use. Arousal levels, gender/sex, inflammation, and the timing of stress exposure play a role in the vulnerability of these circuits. The current review focuses on how early postnatal stress impacts brain development during a sensitive period to increase externalizing and internalizing behaviors in adolescence that include social interactions (aggression; sexual activity), working memory impairment, and depression. How stress effects the developmental trajectories of brain circuits that are associated with addiction are discussed for both clinical and preclinical studies.

Exposure to environmental enrichment attenuates addiction-like behavior and alters molecular effects of heroin self-administration in rats

Environmental factors profoundly affect the addictive potential of drugs of abuse and may also modulate the neuro-anatomical/neuro-chemical impacts of uncontrolled drug use and relapse propensity. This study examined the impact of environmental enrichment on heroin self-administration, addiction-related behaviors, and molecular processes proposed to underlie these behaviors. Male Sprague-Dawley rats in standard and enriched housing conditions intravenously self-administered similar amounts of heroin over 14 days. However, environmental enrichment attenuated progressive ratio, extinction, and reinstatement session responding after 14 days of enforced abstinence. Molecular mechanisms, namely DNA methylation and gene expression, are proposed to underlie abstinence-persistent behaviors. A global reduction in methylation is reported to coincide with addiction, but no differences in total genomic methylation or repeat element methylation were observed in CpG or non-CpG (CH) contexts across the mesolimbic circuitry as assessed by multiple methods including whole genome bisulfite sequencing. Immediate early gene expression associated with drug seeking, taking, and abstinence also were examined. EGR1 and EGR2 were suppressed in mesolimbic regions with heroin-taking and environmental enrichment. Site-specific methylation analysis of EGR1 and EGR2 promoter regions using bisulfite amplicon sequencing (BSAS) revealed hypo-methylation in the EGR2 promoter region and EGR1 intragenic CpG sites with heroin-taking and environmental enrichment that was associated with decreased mRNA expression. Taken together, these findings illuminate the impact of drug taking and environment on the epigenome in a locus and gene-specific manner and highlight the need for positive, alternative rewards in the treatment and prevention of drug addiction.

Social Influences in Animal Models of Opiate Addiction

Opiate addiction has reached an epidemic prevalence in recent years, yet social influences on the use and abuse of opiates has been widely understudied. In particular, the neurobiological substrates of opiate addiction and their modulation by social influences are largely unknown, perhaps due to the lack of widespread incorporation of social variables into animal models of opiate addiction. As reviewed here, animal models such as oral and intravenous drug self-administration, conditioned place preference, behavioral sensitization, and the effects of various stressors, have been useful in identifying some of the neurochemical circuitry that mediate social influences on opiate addiction. However, it is clear from our review that newer paradigms that incorporate various social elements are greatly needed to provide more translational insights into the neurobiological basis of opiate addiction. These elements include social and environmental enrichment, presence of conspecifics, and procedures that require subjects to exert effort to engage in prosocial behavior. A wider implementation of social variables into animal models of opiate addiction will help inform neurobehavioral strategies to increase the efficacy of treatment.

The role of the vasopressin system and dopamine D1 receptors in the effects of social housing condition on morphine reward

BACKGROUND

The association with opioid-abusing individuals or even the perception of opioid abuse by peers are risk factors for the initiation and escalation of abuse. Similarly, we demonstrated that morphine-treated animals housed with only morphine-treated animals (referred to as morphine only) acquire morphine conditioned place-preference (CPP) more readily than morphine-treated animals housed with drug-naïve animals (referred to as morphine cage-mates). However, the molecular mechanisms underlying these effects are still elusive.

METHODS

Mice received repeated morphine or saline while housed as saline only, morphine only, or cage-mates. Then, they were examined for the expression levels of D1 dopamine receptor (D1DR), D2 dopamine receptor (D2DR), dopamine transporter (DAT), oxytocin, and Arginine-vasopressin (AVP) in the striatum using qPCR. Additionally, we examined the effects of the AVP-V1b receptor antagonist, SSR149415, on the acquisition of morphine conditioned place-preference (CPP).

RESULTS

Increased striatal expression of D1DR and AVP was observed in morphine only animals, but not morphine cage-mates. No significant effects were observed on the striatal expression of D2DR, DAT, or oxytocin. Antagonizing the AVP-V1b receptors decreased the acquisition of morphine CPP in the morphine only mice, but did not alter the acquisition of morphine CPP in the morphine cage-mate mice.

CONCLUSIONS

Housing with drug-naïve animals protects against the increase in striatal expression of D1DR and AVP elicited by morphine exposure. Moreover, our studies suggest that the protective effect of housing with drug-naïve animals on the acquisition of morphine reward might be, at least partially, mediated by AVP.

Considering the context: social factors in responses to drugs in humans

BACKGROUND

Drugs are typically used in social settings. Here, we consider two factors that may contribute to this observation: (i) the presence of other people may enhance the positive mood effects of a drug, and conversely, (ii) drugs may enhance the value of social stimuli.

METHODS

We review evidence from controlled laboratory studies with human volunteers, which investigated either of these interactions between social factors and responses to drugs. We examine the bidirectional effects of social stimuli and single doses of alcohol, stimulants, opioids, and cannabis.

RESULTS

All four classes of drugs interact with social contexts, but the nature of these interactions varies across drugs, and depends on whether the context is positive or negative.

CONCLUSIONS

Alcohol and stimulant drugs enhance the attractiveness of social stimuli and the desire to socialize, and social contexts, in turn, enhance these drugs' effects. In contrast, opioids and cannabis have subtler effects on social interactions and their effects are less influenced by the presence of others. Overall, there is stronger evidence that drugs enhance positive social contexts than that they dampen the negativity of unpleasant social settings. Controlled research is needed to understand the interactions between drugs of abuse and social contexts, to model and understand the determinants of drug use outside the laboratory.