Does ±3,4-methylenedioxymethamphetamine (ecstasy) induce subjective feelings of social connection in humans? A multilevel meta-analysis

Regan and colleagues frame MDMA (ecstasy) as a psychostimulant historically associated with energising, euphoric and connecting effects, and note its renewed therapeutic interest, particularly in Phase II trials for treatment-resistant PTSD. Earlier experimental work has reported increases in self-reported feelings such as lovingness, friendliness and talkativeness after MDMA, but most individual studies have small sample sizes and there has been no quantitative synthesis to establish the average magnitude of these subjective sociability effects. This paper aims to fill that gap by conducting a multilevel meta-analysis of placebo-controlled human experiments to estimate the overall effect size of MDMA on self-reported sociability-related outcomes. The investigators also plan meta-regressions to explore moderators, specifically MDMA dose and the type of sociability measure used (for example, feeling talkative versus friendly).

The study is a multilevel meta-analysis restricted to placebo-controlled human experiments that reported self‑report measures of felt sociability (for example, friendliness, talkativeness, extraversion-type state ratings). The literature search began with reference lists of two prior reviews and extended to PsycINFO and PubMed up to December 2020 using MDMA combined with terms such as social*, extraver*, talkative*, prosocial*, friendl*, and "subjective effects"; the first author screened abstracts and full texts, and inclusion decisions were verified by a second author. Principal investigators of MDMA labs were contacted for unpublished work. Inclusion criteria required placebo‑controlled human studies measuring self‑reported sociability. Cross-sectional, clinical trials and animal studies were excluded; many included studies used within-subject designs and single-item visual analogue scales (VAS) or established mood scales (for example, AMRS, Bond and Lader, POMS). After screening and risk-of-bias assessment with the Cochrane tool, the authors selected experiments reporting relevant self-report outcomes; some studies contributed multiple effect sizes because they measured more than one sociability item. Effect sizes were computed as Cohen's d for within-subject comparisons, converting reported statistics (partial η2, r, F, t, or means and standard errors) when necessary. A within-person correlation (the correlation of participants' sociability ratings across MDMA and placebo sessions) was assumed to be 0.5 for primary calculations; sensitivity analyses repeated the meta-analysis using correlations from 0 to 0.9 in steps of 0.1 and reportedly produced similar results. Because multiple effect sizes were nested within studies, a three-level multilevel meta-analytic model was used to account for variance at the effect-size, outcome-within-study, and between-study levels; practically, results are discussed as effect sizes nested within studies since participant-level data were not available. The screening initially yielded 32 articles and 61 effect sizes; five outlier studies (defined as effect sizes whose 95% CI bounds lay beyond the pooled effect CI bounds) were excluded, leaving 27 studies contributing 54 effect sizes to the final analysis. The authors also assessed publication bias using funnel plots and a rank correlation test.

The final meta-analysis synthesised 54 effect sizes from 27 studies, representing 592 participants across 30 within-person conditions (some between-subject conditions were treated as separate within-person conditions). The pooled within-subject effect of MDMA versus placebo on self-reported sociability-related outcomes was moderate-to-large: Cohen's d = 0.86 (95% CI [0.68, 1.04]), corresponding to r = 0.39 (95% CI [.32, .46]). A Q-test indicated significant heterogeneity among effect sizes (χ2(53) = 173.1, p = 1.2 × 10^-14). To test whether the size of effects varied by type of sociability measure, outcomes were grouped into extraversion, friendliness, loving, and sociability categories. A meta-regression using extraversion as the reference found no significant omnibus difference across these outcome types (F(3, 50) = 1.17, p = .33), and pairwise contrasts versus extraversion were non-significant (for example, loving: b = 0.22, 95% CI [-0.09, 0.52], p = .16). A separate meta-regression examined maximum MDMA dosage (for weight‑adjusted studies an average 70 kg participant was assumed). This analysis found a small but statistically significant positive relationship between dose and effect size: b = 0.01 per mg (95% CI [0.00, 0.02], p = .004), indicating that the Cohen's d increased by about .01 for each additional milligram of MDMA in the maximum dose metric used. Publication-bias diagnostics suggested asymmetry. The funnel plot exhibited clear evidence of bias and a rank correlation test showed a significant positive relationship between effect size and variance (τ = .50, p = 2.3 × 10^-8), meaning smaller studies tended to report larger effects. The authors note that, given the resource intensity of experimental MDMA research, this asymmetry is unlikely to be a simple file-drawer phenomenon but may reflect unreported null or negative effects on particular sociability measures. Risk-of-bias assessment reported overall low risk; most studies were double-blind with concealed placebo conditions.

Regan and colleagues interpret the pooled moderate-to-large effect (d = 0.86) as consistent with prior theoretical and experimental work indicating that MDMA uniquely enhances subjective social connection. They emphasise that these effects are observed even though most experiments tested participants in isolation with minimal interpersonal contact. The authors briefly review plausible psychosocial and biological mechanisms. Psychologically, MDMA may increase emotional empathy (feeling another's emotion) more than cognitive empathy, and create a positive mood bias that directs attention and concern toward others' positive affect. Biologically, MDMA has been associated with reduced threat-related neural reactivity (for example, attenuated amygdala responses to angry faces) and increased reward-related responses (for example, ventral striatum response to happy faces), and its serotonergic action elevates oxytocin levels. Together, diminished threat perception, increased social reward salience and a positivity bias might account for increased felt sociability and reported closeness or trust. The paper highlights MDMA as a potential social catalyst: when other people are present experimental effects such as increased interaction time, drug liking and confidence are amplified. One randomised study that varied social context found heightened physiological and subjective responses in the presence of others versus being alone or merely observed by a research assistant; the authors recommend systematic manipulation of social and environmental contexts in future work to test moderation by context. Clinical implications are discussed cautiously. While this meta-analysis did not include clinical samples, the authors note that MDMA-assisted psychotherapy has shown promise for PTSD and may be relevant to other conditions with social deficits such as alcohol use disorder or social anxiety in autism. They propose that increased sociability could bolster the therapeutic alliance in psychotherapeutic settings, but stress that mechanistic work is needed to determine whether subjective feelings of sociability directly mediate behavioural change or operate via other pathways. Key limitations acknowledged include significant heterogeneity across studies, the predominance of single-item VAS measures rather than comprehensive validated scales, reliance on placebo rather than active-control comparisons in the pooled estimates, small sample sizes driven by the difficulty of conducting MDMA research, and limited generalisability because participants were largely healthy, young and from Western, educated populations. The authors recommend inclusion of active controls, broader batteries of self-report and indirect measures (for example, behavioural synchrony, language matching), and studies that examine demographic moderators and age effects. Overall, the authors position their findings as a quantitative demonstration that MDMA reliably increases self-reported sociability in experimental settings, and they urge further controlled work to unpack mechanisms, contextual moderators and clinical relevance.

The authors conclude that MDMA produces moderate-to-large increases in self-reported feelings of sociability (for example, feeling outgoing, loving, talkative and friendly) in placebo-controlled experimental studies, despite testing conditions that typically preclude social interaction. They suggest that these subjective effects could be even stronger in real-world social contexts and that MDMA may have meaningful implications for therapeutic encounters and for alleviating loneliness or social deficits. Finally, they call for more research in social and clinical settings to clarify mechanisms and practical applications.