The 3,4-methylenedioxymethamphetamine enhances early visual processing for salient socio-emotional stimuli

The 3,4-methylenedioxymethamphetamine (MDMA) has long been used non-medically, and it is currently under investigation for its potential therapeutic benefits. Both uses may be related to its ability to enhance empathy, sociability, emotional processing and its anxiolytic effects. However, the neural mechanisms underlying these effects, and their specificity to MDMA compared to other stimulants, are not yet fully understood. Here, using electroencephalography (EEG), we investigated the effects of MDMA and a prototypic stimulant, methamphetamine (MA), on early visual processing of socio-emotional stimuli in an oddball emotional faces paradigm. Specifically, we examined whether MDMA or MA enhance the processing of facial expressions, compared to placebo, during the early stages of visual perception. MDMA enhanced an event-related component that is sensitive to detecting faces (N170), specifically for happy and angry expressions compared to neutral faces. MA did not affect this measure, and neither drug altered other components of the response to emotional faces. These findings provide novel insights into the neural mechanisms underlying the effects of MDMA on socio-emotional processing and may have implications for the therapeutic use of MDMA in the treatment of social anxiety and other psychiatric disorders.

MDMA enhances positive affective responses to social feedback

BACKGROUND

The prosocial compound ± 3,4-methylenedioxymethamphetamine (MDMA) is an amphetamine derivative that has shown promise as an adjunct to psychotherapy in the treatment of post-traumatic stress disorder. MDMA increases positive responses to social images, and it has been suggested that the ability of MDMA to positively bias social perception may underlie its therapeutic efficacy as a psychotherapy adjunct. However, the effect of the compound on affective responses to positive or negative social feedback has not been tested.

AIMS

In this study, we aimed to test the effects of MDMA compared to placebo and the prototypical stimulant, methamphetamine (MA), on responses to positive and negative social feedback.

METHODS

This was a double-blind, placebo-controlled, crossover trial (NCT03790618), comparing the effects of two doses of MDMA (0.75 mg/kg, 1.5 mg/kg) to both placebo and MA (20 mg) on responses to a personalized social feedback task, similar to a dating app, in healthy adult volunteers ages 18-40 (N = 36, 18 women, 18 men).

RESULTS/OUTCOMES

The high dose of MDMA increased positive affective responses to social feedback.

CONCLUSIONS/INTERPRETATIONS

These findings suggest one process by which MDMA may facilitate social connection. Further work is needed to understand how MDMA affects responses to more generalized types of social feedback and to understand these effects in clinical populations.

Altered States and Social Bonds: Effects of MDMA and Serotonergic Psychedelics on Social Behavior as a Mechanism Underlying Substance-Assisted Therapy

There has been renewed interest in the use of 3,4-methylenedioxy-methamphetamine (MDMA) and serotonergic psychedelics in the treatment of multiple psychiatric disorders. Many of these compounds are known to produce prosocial effects, but how these effects relate to therapeutic efficacy and the extent to which prosocial effects are unique to a particular drug class is unknown. In this article, we present a narrative overview and compare evidence for the prosocial effects of MDMA and serotonergic psychedelics to elucidate shared mechanisms that may underlie the therapeutic process. We discuss 4 categories of prosocial effects: altered self-image, responses to social reward, responses to negative social input, and social neuroplasticity. While both categories of drugs alter self-perception, MDMA may do so in a way that is less related to the experience of mystical-type states than serotonergic psychedelics. In the case of social reward, evidence supports the ability of MDMA to enhance responses and suggests that serotonergic psychedelics may also do so, but more research is needed in this area. Both drug classes consistently dampen reactivity to negative social stimuli. Finally, preclinical evidence supports the ability of both drug classes to induce social neuroplasticity, promoting adaptive rewiring of neural circuits, which may be helpful in trauma processing. While both MDMA and serotonergic psychedelics produce prosocial effects, they differ in the mechanisms through which they do this. These differences affect the types of psychosocial interventions that may work best with each compound.

Social Psychopharmacology: Novel Approaches to Treat Deficits in Social Motivation in Schizophrenia

BACKGROUND AND HYPOTHESIS

Diminished social motivation is a negative symptom of schizophrenia and leads to severe functional consequences for many patients suffering from the illness. However, there are no effective medications available to treat this symptom. Despite the lack of approved treatments for patients, there is a growing body of literature on the effects of several classes of drugs on social motivation in healthy volunteers that may be relevant to patients. The aim of this review is to synthesize these results in an effort to identify novel directions for the development of medications to treat reduced social motivation in schizophrenia.

STUDY DESIGN

In this article, we review pharmacologic challenge studies addressing the acute effects of psychoactive drugs on social motivation in healthy volunteers and consider how these findings may be applied to deficits in social motivation in schizophrenia. We include studies testing amphetamines and 3,4-methylenedioxymethamphetamine (MDMA), opioids, cannabis, serotonergic psychedelics, antidepressants, benzodiazepines, and neuropeptides.

STUDY RESULTS

We report that amphetamines, MDMA, and some opioid medications enhance social motivation in healthy adults and may represent promising avenues of investigation in schizophrenia.

CONCLUSIONS

Given the acute effects of these drugs on behavioral and performance-based measures of social motivation in healthy volunteers, they may be particularly beneficial as an adjunct to psychosocial training programs in patient populations. It remains to be determined how these medications affect patients with deficits in social motivation, and in which contexts they may be most effectively administered.

Does acute stress play a role in the lasting therapeutic effects of psychedelic drugs?

Psychedelic drugs, when used in the context of psychotherapy, can produce significant and long-lasting memories with enduring beneficial effects. Yet, the behavioral and neurobiological mechanisms that underlie these beneficial effects remain a mystery. Here, we suggest that both the quality and durability of memories of the drug-facilitated therapeutic experience may be mediated, in part, by the acute stress responses induced by the drugs. It is known that high doses of psychedelic drugs activate autonomic and hormonal stress responses. For evolutionarily adaptive reasons, acute stress is known to i) instill meaning to the immediate context in which it is experienced, and ii) lead to the formation of salient and lasting memories of the events surrounding the stress. Thus, the stress-inducing effect of psychedelic drugs may contribute to the reported sense of meaning, as well as the durability of the memory of the drug experience. When used in a therapeutic context these actions may i) enhance the salience of insights gained during the experience and ii) strengthen the memories formed by these experiences. Future empirical studies will help to determine whether acute stress contributes to the emotional significance and lasting effects of psychedelic-assisted psychotherapy.

Challenges in translational research: MDMA in the laboratory versus therapeutic settings

Despite substantial progress in the use of mind-altering drugs to treat psychiatric disorders, the psychological processes through which these drugs change mood or behavior are poorly understood. Controlled laboratory studies with well-defined psychological constructs are valuable to understand how these drugs manifest their therapeutic benefit. However, there are substantial methodological differences between clinical studies investigating therapeutic outcome and laboratory studies investigating the processes that might underlie the therapeutic effects. Here, we examine some of these differences using the example of 3,4-methylenedioxymethamphetamine (MDMA). We review differences in expectancies, social and physical context, participant characteristics, pharmacological factors, and outcome measures in studies with participants who do or do not have psychiatric diagnoses. We describe the challenges and opportunities in translating findings from laboratory studies to the clinic and identify ways to bridge the gap between these approaches.

Effects of Acute Drug Administration on Emotion: A Review of Pharmacological MRI Studies

Purpose of review

Many drug users claim to use drugs to cope with negative emotions, which may, in turn, result in persistent emotional blunting or anhedonia even when they are not using drugs. The purpose of this review is to describe the ways acute administration of psychoactive drugs impacts brain regions during emotion-related tasks, as a first step in understanding how drugs influence emotion processing in the brain.

Recent findings

Drugs have varying effects on neural responses to emotional stimuli. In general, alcohol, analgesics, and psychedelics reduce neural reactivity to negative emotional stimuli in the amygdala and other brain regions. Other drugs produce mixed effects: Stimulants such as caffeine and modafinil increase brain activation while viewing emotional stimuli, whereas MDMA decreases activation during presentation of negative images. The effects of cannabinoids (cannabidiol and THC) are mixed. There are also inconsistent findings on the associations between neural responses to emotional stimuli and subjective drug effects.

Summary

Consistent with the notion that individuals might use drugs non-medically to diminish the experience of negative emotions, several drugs of abuse decrease neural responses to negative stimuli in limbic brain regions. These neural actions may underlie the reported 'emotional blunting' of drugs, which may contribute to drug-seeking behavior. Future work is needed to examine these limbic responses in relation to self-reports of changes in affect, both during acute administration and after extended drug use.

Effects of Intranasal Oxytocin on Stress-Induced Cigarette Craving in Daily Smokers

BACKGROUND

Cigarette smoking is a well-known public health concern, and there is an urgent need to develop new treatments to reduce smoking or facilitate abstinence. One factor that is known to contribute to relapse is stress, making the stress response an important target for treatment. The neuropeptide oxytocin (OT) is believed to have stress-reducing effects, and in addition there is evidence that it reduces drug craving. The purpose of the present study was to examine the effects of intranasal OT on stress-induced cigarette craving in regular smokers after 12 h of abstinence.

METHOD

Daily smokers (n = 48) completed a stress induction task and a nonstressful control task at two different sessions, receiving intranasal OT (40 IU) or placebo (PBO) before or after the task. Subjects were randomly assigned to one of three groups: Group PP (n = 16) received PBO before and after the stress/control tasks, Group OP (n = 16) received OT before the tasks and PBO after, and Group PO (n = 16) received PBO before the tasks and OT shortly after completing the tasks. Cigarette craving as well as subjective and physiological responses to stress was assessed.

RESULTS

OT did not alter responses to stress, whether it was administered before or after the stressful task, on measures of cigarette craving, anxiety, heart rate, blood pressure, and cortisol levels.

CONCLUSIONS

The current study findings do not support several previous reports that OT reduced either stress or drug craving.

IMPLICATIONS

This study finds a null result of the neuropeptide oxytocin on stress-induced cigarette craving. Reporting null findings is part of the process of identifying potential treatments for addictive disorders.

Preliminary Report on the Effects of a Low Dose of LSD on Resting-State Amygdala Functional Connectivity

BACKGROUND

The practice of "microdosing," or the use of repeated, very low doses of lysergic acid diethylamide (LSD) to improve mood or cognition, has received considerable public attention, but empirical studies are lacking. Controlled studies are needed to investigate both the therapeutic potential and the neurobiological underpinnings of this pharmacologic treatment.

METHODS

The present study was designed to examine the effects of a single low dose of LSD (13 μg) versus placebo on resting-state functional connectivity and cerebral blood flow in healthy young adults. Twenty men and women, 18 to 35 years old, participated in 2 functional magnetic resonance imaging scanning sessions in which they received placebo or LSD under double-blind conditions. During each session, the participants completed drug effect and mood questionnaires, and physiological measures were recorded. During expected peak drug effect, they underwent resting-state blood oxygen level-dependent and arterial spin labeling scans. Cerebral blood flow as well as amygdala and thalamic connectivity were analyzed.

RESULTS

LSD increased amygdala seed-based connectivity with the right angular gyrus, right middle frontal gyrus, and the cerebellum, and decreased amygdala connectivity with the left and right postcentral gyrus and the superior temporal gyrus. This low dose of LSD had weak and variable effects on mood, but its effects on positive mood were positively correlated with the increase in amygdala-middle frontal gyrus connectivity strength.

CONCLUSIONS

These preliminary findings show that a very low dose of LSD, which produces negligible subjective changes, alters brain connectivity in limbic circuits. Additional studies, especially with repeated dosing, will reveal whether these neural changes are related to the drug's purported antidepressant effect.

Acute Subjective and Behavioral Effects of Microdoses of Lysergic Acid Diethylamide in Healthy Human Volunteers

BACKGROUND

Numerous anecdotal reports suggest that repeated use of very low doses of lysergic acid diethylamide (LSD), known as microdosing, improves mood and cognitive function. These effects are consistent both with the known actions of LSD on serotonin receptors and with limited evidence that higher doses of LSD (100-200 μg) positively bias emotion processing. Yet, the effects of such subthreshold doses of LSD have not been tested in a controlled laboratory setting. As a first step, we examined the effects of single very low doses of LSD (0-26 μg) on mood and behavior in healthy volunteers under double-blind conditions.

METHODS

Healthy young adults (N = 20) attended 4 laboratory sessions during which they received 0 (placebo), 6.5, 13, or 26 μg of LSD in randomized order at 1-week intervals. During expected peak drug effect, they completed mood questionnaires and behavioral tasks assessing emotion processing and cognition. Cardiovascular measures and body temperature were also assessed.

RESULTS

LSD produced dose-related subjective effects across the 3 doses (6.5, 13, and 26 μg). At the highest dose, the drug also increased ratings of vigor and slightly decreased positivity ratings of images with positive emotional content. Other mood measures, cognition, and physiological measures were unaffected.

CONCLUSIONS

Single microdoses of LSD produced orderly dose-related subjective effects in healthy volunteers. These findings indicate that a threshold dose of 13 μg of LSD might be used safely in an investigation of repeated administrations. It remains to be determined whether the drug improves mood or cognition in individuals with symptoms of depression.

Effects of opioid- and non-opioid analgesics on responses to psychosocial stress in humans

Both preclinical and clinical evidence suggests that the endogenous opioid system is involved in responses to stress. For example, in animal models opioid agonists reduce isolation distress whereas opioid antagonists increase isolation distress. We recently reported that the mixed mu agonist and kappa antagonist buprenorphine dampened responses to acute psychosocial stress in humans. Now we extend this to study the effects of a pure mu-opioid agonist, hydromorphone, and a non-opioid analgesic, acetaminophen, on response to social stress. We compared the effect of hydromorphone (2 and 4 mg), acetaminophen (1000 mg) to a placebo using a between subject design. Healthy adult volunteers were randomly assigned to receive placebo (N = 13), 2 mg hydromorphone (N = 12), 4 mg hydromorphone (N = 12), or 1000 mg acetaminophen (paracetamol; N = 13) under double-blind conditions before undergoing a stress task or a control task on two separate sessions. The stress task, consisting of a standardized speaking task and the non-stressful control task were presented in counterbalanced order. Dependent measures included mood ratings, subjective appraisal of the stress (or no-stress) task, salivary cortisol, pupil diameter, heart rate, and blood pressure. The stress task produced its expected increase in heart rate, blood pressure, salivary cortisol, pupil diameter, and subjective ratings of anxiety and negative mood. Hydromorphone dose-dependently dampened cortisol responses to stress, and decreased ratings of how "challenging" participants found the task. Acetaminophen did not affect physiological responses, but, like hydromorphone, decreased ratings of how "challenging" the task was. The hydromorphone results support the idea that the mu-opioid system is involved in physiological responses to acute stress in humans, in line with results from preclinical studies. The non-opioid analgesic acetaminophen did not dampen physiological responses, but did reduce some components of psychological stress. It remains to be determined how both opioid and non-opioid systems mediate the complex physiological and psychological responses to social stress.

Pharmacological challenge studies with acute psychosocial stress

Chronic stress is known to affect many psychiatric disorders, and studies of responses to acute stress may reveal processes that ultimately lead to maladaptive responses to chronic stress. Many studies have used simulated public speaking tasks to induce stress in the laboratory and, of interest to this review, the tasks have been used to assess the effects of both therapeutic and nonmedical drugs on stress reactivity. Here we review 38 studies that examined effects of single doses of drugs on subjective, cardiovascular and hormonal responses to an acute social stressor in healthy volunteers. Most studies have used the Trier Social Stress Test (TSST), or variations on it involving public speaking or mental arithmetic. Pharmacological studies with the TSST (ph-TSST) have been conducted for three main reasons: i) to determine the clinical effectiveness of psychiatric medications to reduce stress responses, ii) to investigate the neurochemical mechanisms involved in the stress response, and iii) to determine whether drugs of abuse relieve, or occasionally worsen, responses to acute stress. The review indicates that standard anxiolytic medications consistently reduce subjective responses to the TSST, whereas single doses of antidepressants produce mixed effects. Mechanistic studies indicate that several neurotransmitter systems are involved in the stress response, including serotonin, norepinephrine, GABA, glutamate, opioids, and endocannabinoids. Among drugs of abuse, alcohol and cannabinoids exert some stress-dampening effects, whereas caffeine, nicotine, and amphetamines tend to increase stress responses. Comparing outcome measures of the responses to stress, subjective ratings of anxiety are among the most sensitive indices of the stress response, with cortisol levels second and cardiovascular responses least sensitive. We conclude that the TSST is a valuable tool to study the clinical effectiveness of medications for stress-related disorders, and that it is important to use standardized procedures to enable comparisons across studies.

Effects of Buprenorphine on Responses to Emotional Stimuli in Individuals with a Range of Mood Symptomatology

BACKGROUND

The opioid drug buprenorphine has been shown to modify responses to emotional stimuli and may have antidepressant properties. In preclinical studies, it shows antidepressant-like and anxiolytic-like effects, and a handful of clinical studies suggest it may reduce symptoms of depression in patients. We have shown that low doses of buprenorphine reduce responses to negative emotional stimuli in healthy adults. Here we extended these findings to individuals with symptoms of depression and anxiety.

METHODS

We examined the effects of buprenorphine on attention to emotional facial expressions and ratings of and psychophysiological responses to emotional images in adults with a range of mood symptomatology. Volunteers (n=38) were recruited with low, mild, moderate, and severe scores on the Depression-Anxiety-Stress Scale. They attended 2 laboratory sessions during which they received either placebo or 0.2 mg sublingual buprenorphine in randomized order under double-blind conditions. During peak drug effect, participants completed a visual attention task assessing responses to emotional faces and a picture-rating task assessing responses to emotional images with and without social content.

RESULTS

Buprenorphine reduced attention to fearful facial expressions as it did in our previous study, and the emotion-specific effect was especially pronounced in individuals with high Depression-Anxiety-Stress Scale scores. The drug also increased ratings of positivity of images with social content, but this effect was less strong in individuals with higher Depression-Anxiety-Stress Scale scores.

CONCLUSIONS

These results suggest low doses of buprenorphine may reduce some dimensions of responses to negative emotional stimuli in individuals high on depression or anxiety, while leaving other dimensions unaffected.

MDMA does not alter responses to the Trier Social Stress Test in humans

RATIONALE

±3,4-Methylenedioxymethamphetamine (MDMA, "ecstasy") is a stimulant-psychedelic drug with unique social effects. It may dampen reactivity to negative social stimuli such as social threat and rejection. Perhaps because of these effects, MDMA has shown promise as a treatment for post-traumatic stress disorder (PTSD). However, the effect of single doses of MDMA on responses to an acute psychosocial stressor has not been tested.

OBJECTIVES

In this study, we sought to test the effects of MDMA on responses to stress in healthy adults using a public speaking task. We hypothesized that the drug would reduce responses to the stressful task.

METHODS

Volunteers (N = 39) were randomly assigned to receive placebo (N = 13), 0.5 mg/kg MDMA (N = 13), or 1.0 mg/kg MDMA (N = 13) during a stress and a no-stress session. Dependent measures included subjective reports of drug effects and emotional responses to the task, as well as salivary cortisol, heart rate, and blood pressure.

RESULTS

The stress task produced its expected increase in physiological responses (cortisol, heart rate) and subjective ratings of stress in all three groups, and MDMA produced its expected subjective and physiological effects. MDMA alone increased ratings of subjective stress, heart rate, and saliva cortisol concentrations, but contrary to our hypothesis, it did not moderate responses to the Trier Social Stress Test.

CONCLUSIONS

Despite its efficacy in PTSD and anxiety, MDMA did not reduce either the subjective or objective responses to stress in this controlled study. The conditions under which MDMA relieves responses to negative events or memories remain to be determined.

The effects of MDMA on socio-emotional processing: Does MDMA differ from other stimulants?

±3,4-Methylenedioxymethamphetamine (MDMA) is a popular recreational drug that enhances sociability and feelings of closeness with others. These "prosocial" effects appear to motivate the recreational use of MDMA and may also form the basis of its potential as an adjunct to psychotherapy. However, the extent to which MDMA differs from prototypic stimulant drugs, such as dextroamphetamine, methamphetamine, and methylphenidate, in either its behavioral effects or mechanisms of action, is not fully known. The purpose of this review is to evaluate human laboratory findings of the social effects of MDMA compared to other stimulants, ranging from simple subjective ratings of sociability to more complex elements of social processing and behavior. We also review the neurochemical mechanisms by which these drugs may impact sociability. Together, the findings reviewed here lay the groundwork for better understanding the socially enhancing effects of MDMA that distinguish it from other stimulant drugs, especially as these effects relate to the reinforcing and potentially therapeutic effects of the drug.

Effects of d-amphetamine upon psychosocial stress responses

Psychostimulant drugs alter the salience of stimuli in both laboratory animals and humans. In animals, stimulants increase rates of responding to conditioned incentive stimuli, and in humans, amphetamine increases positive ratings of emotional images. However, the effects of stimulants on real-life emotional events have not been studied in humans. In this study, we examined the effect of d-amphetamine on responses to acute psychosocial stress using a public speaking task. Healthy volunteers (N=56) participated in two experimental sessions, one with a psychosocial stressor (the Trier Social Stress Test) and one with a non-stressful control task. They were randomly assigned to receive d-amphetamine (5 mg n=18, 10 mg n=20) or placebo (n=18) on both sessions under double blind conditions. Salivary cortisol, subjective mood, and vital signs were measured at regular intervals during the session. Subjects also provided cognitive appraisals of the tasks before and after their performances. Amphetamine produced its expected mood and physiological effects, and the Trier Social Stress Test produced its expected effects on cortisol and mood. Although neither dose of amphetamine altered cardiovascular or hormonal responses to stress, amphetamine (10 mg) increased participants' pre-task appraisals of how challenging the task would be, and it increased post-task ratings of self-efficacy. Paradoxically, it also increased ratings of how stressful the task was, and prolonged aversive emotional responses. These findings suggest that amphetamine differentially affects stress response components: it may increase participants' appraisals of self-efficacy without dampening the direct emotional or physiological responses to the stress.

Naltrexone alters the processing of social and emotional stimuli in healthy adults

Endogenous opioids have complex social effects that may depend on specific receptor actions and vary depending on the "stage" of social behavior (e.g., seeking vs. responding to social stimuli). We tested the effects of a nonspecific opioid antagonist, naltrexone (NTX), on social processing in humans. NTX is used to treat alcohol and opiate dependence, and may affect both mu and kappa-opioid systems. We assessed attention ("seeking"), and subjective and psychophysiological responses ("responding") to positive and negative social stimuli. Based on literature suggesting mu-opioid blockade impairs positive social responses, we hypothesized that NTX would decrease responses to positive social stimuli. We also tested responses to negative stimuli, which might be either increased by NTX's mu-opioid effects or decreased by its kappa-opioid effects. Thirty-four healthy volunteers received placebo, 25 mg, or 50 mg NTX across three sessions under double-blind conditions. At each session, participants completed measures of attention, identification, and emotional responses for emotional faces and scenes. NTX increased attention to emotional expressions, slowed identification of sadness and fear, and decreased ratings of arousal for social and nonsocial emotional scenes. These findings are more consistent with anxiolytic kappa-antagonist than mu-blocking effects, suggesting effects on kappa receptors may contribute to the clinical effects of NTX.

Effects of buprenorphine on responses to social stimuli in healthy adults

In addition to its classical role in mediating responses to pain, the opioid system is strongly implicated in the regulation of social behavior. In young laboratory animals, low doses of opioid analgesic drugs reduce responses to isolation distress and increase play behavior. However, little is known about how opioid drugs affect responses to social stimuli in humans. Here we examined the effects of buprenorphine, a mu-opioid partial agonist and kappa-antagonist, on three dimensions of social processing: (i) responses to simulated social rejection, (ii) attention to emotional facial expressions, and (iii) emotional responses to images with and without social content. Healthy adults (N=36) attended two sessions during which they received either placebo or 0.2mg sublingual buprenorphine in randomized order, under double-blind conditions. Ninety minutes after drug administration, they completed three behavioral tasks: (i) a virtual ball-toss game in which they were first included and then excluded by the other players; (ii) an attention task in which they were shown pairs of faces (one emotional and one neutral), while the direction of their gazes was recorded using electrooculography, and (iii) a picture-viewing task, in which they rated standardized images with and without social content. During the ball-toss game, buprenorphine decreased perceived social rejection. During the attention task, the drug reduced initial attention to fearful facial expressions, without influencing attention to angry, happy, or sad faces. Finally, during the picture-viewing task, buprenorphine increased ratings of positivity of images with social content without affecting ratings of nonsocial images. These results suggest that even at low doses, opioid analgesic drugs reduce responses to some types of negative social stimuli while enhancing positive responses to social stimuli. This provides further support for the role of the opioid system in mediating responses to social rejection and social reward.

Opioid partial agonist buprenorphine dampens responses to psychosocial stress in humans

Pre-clinical and clinical evidence indicates that opioid drugs have stress-dampening effects. In animal models, opioid analgesics attenuate responses to isolation distress, and in humans, opioids reduce stress related to anticipation of physical pain. The stress-reducing effects of opioid drugs may contribute to their abuse potential. Despite this evidence in laboratory animals, the effects of opioids on responses to psychosocial stress have not been determined in humans. Here we examined the effects of buprenorphine, a μ-opioid partial agonist used to treat opioid dependence and pain, on subjective and physiological responses to a stressful public speaking task in healthy adults. We hypothesized that buprenorphine would reduce subjective and physiological stress responses. Healthy adult volunteers (N=48) were randomly assigned to receive placebo, 0.2mg sublingual buprenorphine, or 0.4mg sublingual buprenorphine in a two-session study with a stressful speaking task (Trier Social Stress Test; TSST) and a non-stressful control task. During the sessions, the participants reported on their mood states, provided subjective appraisals of the task, and measures of salivary cortisol, heart rate, and blood pressure at regular intervals. Stress produced its expected effects, increasing heart rate, blood pressure, salivary cortisol, and subjective ratings of anxiety and negative mood. In line with our hypothesis, both doses of buprenorphine significantly dampened salivary cortisol responses to stress. On self-report ratings, buprenorphine reduced how threatening participants found the tasks. These results suggest that enhanced opioid signaling dampens responses to social stress in humans, as it does in laboratory animals. This stress-dampening effect of buprenorphine may contribute to the non-medical use of opioid drugs.