Multifaceted empathy of healthy volunteers after single doses of MDMA: a pooled sample of placebo-controlled studies

Kuypers and colleagues situate their study in a literature showing that a single dose of MDMA can increase aspects of sociability and emotional empathy while effects on cognitive empathy have been inconsistent across paradigms. The Multifaceted Empathy Test (MET), which presents complex, ecologically valid images and yields separate measures of cognitive empathy (CE) and emotional empathy (EE), has produced a consistent pattern in smaller placebo-controlled studies: no effect on CE but an increase in EE. Previous work has also reported MDMA-induced rises in peripheral oxytocin, which has been hypothesised to contribute to empathogenic effects, but two prior studies found no relationship between oxytocin levels and behavioural changes in EE. Small sample sizes in earlier studies limited the ability to examine potential moderators such as sex, trait empathy, lifetime ecstasy use, and MDMA or oxytocin plasma concentrations. The present paper pooled data from six placebo-controlled, within-subject studies conducted in two laboratories to evaluate the robustness of MDMA's effects on CE and EE in a larger sample (n = 118). The investigators aimed to confirm whether MDMA enhances EE without affecting CE and to test whether that effect is moderated by sex, trait empathy (Interpersonal Reactivity Index), lifetime ecstasy use, MDMA blood concentrations, or changes in peripheral oxytocin. Pooling data was intended to increase power to detect moderator effects and to assess consistency across doses (75 mg and 125 mg) and sites.

The analysis pooled data from six placebo-controlled, double-blind, within-subject studies of MDMA and empathy: four conducted in Basel, Switzerland, and two in Maastricht, the Netherlands. The combined sample comprised 118 healthy volunteers. Inclusion criteria across studies required good medical health, no personal or first-degree family psychiatric history, and restricted lifetime illicit drug use (Basel: maximum five lifetime uses; Maastricht: minimum three prior ecstasy/MDMA experiences). All studies obtained ethical approval and written informed consent. The extracted text does not clearly report additional demographic details beyond sample size and the general inclusion rules. Each participant completed two test days (MDMA and placebo) separated by at least seven days. MDMA was given orally as a fixed dose of either 75 mg (studies 3, 5, 6) or 125 mg (studies 1, 2, 4). Baseline blood samples were taken prior to administration; additional blood samples for MDMA and oxytocin were collected between 90 and 120 minutes after dosing (timing varied for some studies and was consistently 180 minutes after the 125 mg dose). Urine drug screens and pregnancy tests for women were performed on each test day. Subjective and cardiovascular effects were assessed but are reported elsewhere. Empathy was assessed with the Multifaceted Empathy Test (MET), which uses 40 pictures (50% positive, 50% negative). Cognitive empathy was measured by forced-choice emotion labelling (accuracy), and emotional empathy by two self-ratings per image: implicit EE (arousal; scale 1–9) and explicit EE (concern for the depicted person; scale 1–9). Trait empathy was measured using a shortened Interpersonal Reactivity Index (IRI), with only baseline/placebo IRI data analysed. MDMA and oxytocin concentrations in plasma were assayed at the two sites using different laboratory methods; because oxytocin assays differed, oxytocin change was expressed as percent change from baseline. Statistical analyses used mixed generalized linear models and repeated-measures GLMs. Primary models tested Treatment (placebo, MDMA) and Valence (positive, negative) as within-subject factors, with Study (6 levels) and Dose (75 mg, 125 mg) as between-subject factors; Sex was added in secondary models. IRI scales were examined with multivariate GLM including Study and Sex. Separate GLMs examined effects of Sex and Dose on MDMA blood concentrations, and repeated-measures GLMs tested oxytocin responses. Correlations (Pearson or Spearman as appropriate) explored relationships between MET outcomes and trait empathy, MDMA concentrations, oxytocin %-change, and lifetime ecstasy use. The alpha threshold was p = 0.05 and partial eta-squared values were reported for significant effects.

Cognitive empathy (CE): Performance on the MET showed a robust valence effect: participants were more accurate at recognising positive than negative emotions (Valence F1,112 = 22.80; p < 0.001; partial η2 = 0.17). There were no effects of Treatment (MDMA versus placebo), Study, Dose, Sex, or interactions involving Treatment on CE; in other words, MDMA did not alter accuracy of emotion recognition in the pooled sample. Emotional empathy (EE): Explicit EE (concern) increased under MDMA compared with placebo (Treatment F1,112 = 7.23; p = 0.008; partial η2 = 0.06). A significant Treatment × Valence interaction (F1,112 = 11.15; p = 0.001; partial η2 = 0.09) indicated that MDMA produced a larger increase in concern for positive stimuli than for negative stimuli; post-hoc tests showed higher concern for positive emotions under MDMA versus placebo (t117 = 4.27; p < 0.001) and compared with negative emotions in the placebo condition (t117 = 2.45; p = 0.02). Implicit EE (arousal) was also elevated after MDMA (Treatment F1,112 = 8.68; p = 0.004; partial η2 = 0.08), with a Treatment × Valence interaction (F1,112 = 9.13; p = 0.003; partial η2 = 0.07); MDMA increased arousal for positive (t117 = 4.48; p < 0.001) and, to a lesser extent, negative stimuli (t117 = 2.34; p = 0.02). There were no main effects of Study or Dose or other significant Treatment interactions on EE. Sex and trait empathy: On the IRI, women scored higher than men on the EE-related scales empathic concern (F1,102 = 7.06; p = 0.009) and personal distress (F1,102 = 13.37; p < 0.001). In the MET, females reported greater explicit concern across conditions (Sex main effect F1,106 = 6.41; p = 0.01; partial η2 = 0.06), but Sex did not interact with Treatment, indicating that the MDMA-induced increase in EE occurred similarly in men and women. No sex differences were observed for state CE. MDMA and oxytocin blood concentrations: MDMA plasma concentrations differed by Dose (125 mg > 75 mg; Dose F1,108 = 146.75; p = 0.001; partial η2 = 0.58) and Sex (higher in females; Sex F1,108 = 10.79; p = 0.001; partial η2 = 0.09), with a Sex × Dose interaction (F1,108 = 18.00; p = 0.001; partial η2 = 0.14) driven by disproportionately higher concentrations in females at 125 mg. For the 75 mg condition there was a Study effect on concentrations, and for the 125 mg condition females had higher concentrations than males but no Study effect. Oxytocin percent-change from baseline increased after MDMA versus placebo (Treatment F1,98 = 36.55; p < 0.001; partial η2 = 0.27), with Study differences and a Study × Treatment interaction; Sex had no effect on oxytocin responses. Correlations and lifetime ecstasy use: MDMA blood concentration correlated weakly but significantly with EE for positive emotions: explicit concern r110 = 0.26 (p = 0.005) and arousal r110 = 0.20 (p = 0.04). MDMA dose expressed as mg/kg correlated weakly with explicit concern for positive emotions (r116 = 0.19; p = 0.04). MDMA blood levels were strongly correlated with mg/kg dose (r110 = 0.78; p < 0.001). Oxytocin %-change did not correlate significantly with MET responses in either condition. Lifetime ecstasy use did not correlate with MET measures in placebo or MDMA conditions, but higher lifetime use was associated with lower scores on two IRI scales: Fantasy (r114 = -0.35; p < 0.001) and Personal Distress (r114 = -0.20; p = 0.03).

Pooling data from six placebo-controlled studies, the investigators confirmed that a single dose of MDMA enhances emotional empathy without affecting cognitive empathy on the MET. The MDMA effect on EE manifested in both explicit concern and implicit arousal, and was most pronounced for positively valenced stimuli. The authors suggest this may reflect a mood-congruent processing bias or an increase in 'positive empathy', a state linked to prosocial behaviour and social closeness. They also note the difficulty of fully separating subjective mood effects from task performance given that most participants correctly guessed treatment condition. The pooled analysis indicated that the MDMA-induced EE increase occurred in both sexes and at both doses tested; although women reported higher trait empathic concern and personal distress on the IRI and greater explicit concern on the MET overall, Sex did not moderate the MDMA effect. MDMA blood concentrations and mg/kg dose were positively associated with EE for positive stimuli, suggesting acute drug exposure contributes to the magnitude of the empathogenic response. By contrast, lifetime ecstasy history did not predict MDMA's effects on task-based empathy, implying repeated prior use within the sampled range did not blunt the behavioural EE response. Oxytocin concentrations rose after MDMA administration, but oxytocin changes were not associated with individual differences in behavioural EE. The authors caution that peripheral oxytocin measures may not reflect central oxytocin activity and that methodological differences between studies in oxytocin assays may have limited the ability to detect associations. Limitations acknowledged by the researchers include procedural heterogeneity across studies (variation in timing of the MET, different laboratories and assay methods for MDMA and oxytocin, and the presence of other tasks that may have preceded the MET), which may have introduced inconsistency, particularly for pharmacokinetic and correlational analyses. They also note that women received a higher mg/kg dose on average, which could have masked potential sex differences in behavioural sensitivity. Strengths highlighted include increased statistical power from pooling and balanced representation of male and female participants across sub-studies. The authors conclude that MDMA's enhancement of emotional empathy is robust across laboratories and doses and is not moderated by sex, trait empathy, oxytocin levels, or prior ecstasy use within the sampled ranges.