Effects of MDMA and Intranasal oxytocin on social and emotional processing

Sixty-five healthy volunteers (25 female, 40 male; mean age 23.8 ± 3.9 years) with light-to-moderate prior MDMA exposure (4–40 lifetime uses; mean 15.0 ± 11.2) participated. All participants were Caucasian and met inclusion criteria of age 18–35, at least high school education and BMI 18–30; those with significant medical or psychiatric disorders or heavy smoking were excluded. Women using hormonal contraceptives were tested regardless of cycle phase; others were tested in the follicular phase. The protocol was approved by an institutional review board and participants provided written informed consent. The study used a double-dummy, mixed within–between-subjects design. After orientation, each participant completed four outpatient sessions separated by at least 5 days. In randomized order and under double-blind conditions, participants received one of: placebo, MDMA 0.75 mg/kg, MDMA 1.5 mg/kg, or intranasal oxytocin (either 20 IU or 40 IU). On each session participants swallowed a capsule (MDMA or placebo) at 0930 h and received a nasal spray (oxytocin or placebo) at 1000 h. Forty-three participants received 20 IU oxytocin and 22 received 40 IU. Physiological and subjective measures were recorded at baseline and repeatedly up to 4 h after drug administration. Behavioural tasks were performed between 1030 and 1200 h, the expected peak window for MDMA effects. Physiological monitoring comprised heart rate and blood pressure at regular intervals. Subjective measures included a Drug Effect Questionnaire (DEQ) visual analogue items ('Feel Drug', 'Feel High', 'Like Drug', etc.), a set of visual analogue scales (0–100 mm) for mood and prosocial adjectives (for example, 'Friendly', 'Sociable', 'Playful'), and an End of Session Questionnaire (ESQ) rating desire to take the drug again. Behavioural measures included the Morphed Facial Expression Task (mFER), which presented faces morphed from neutral to full emotion (anger, fear, happiness, sadness) and yielded an accuracy score corrected for false alarms; the Social Evaluation Task (SET), in which participants rated attractiveness, friendliness and trustworthiness of faces; and a Social Choice Task, in which participants rated their desire to engage in a short social activity versus two solitary tasks and then ostensibly engaged in the selected activity (selection was randomised in reality). Drug administration details: MDMA powder was encapsulated at 0.75 and 1.5 mg/kg; intranasal oxytocin (Pitocin) was delivered via atomiser in four administrations to each nare over 15 minutes. Placebo nasal spray differed slightly in formulation (Ocean Spray solution). Data were analysed using multilevel linear models (MLMs). For MDMA analyses fixed effects included drug condition (placebo, 0.75, 1.5 mg/kg), sex and session order, with time included for repeated measures; planned within-subject comparisons were placebo vs active doses and 0.75 vs 1.5 mg/kg. Oxytocin analyses used MLMs with fixed effects drug (placebo vs oxytocin), oxytocin group (20 vs 40 IU), sex and session order. To examine relationships between MDMA- and oxytocin-related prosocial subjective effects, the investigators calculated area-under-the-curve (AUC) for each prosocial item relative to baseline using the trapezoidal method and ran partial correlations controlling for placebo-session ratings. Statistical significance was set at p < 0.05.

Sample characteristics: All 65 volunteers completed the study; 38% were female, mean age 23.8 ± 3.9 years, mean education 14.6 ± 1.4 years, and mean lifetime MDMA uses 15.0 ± 11.2. The two oxytocin groups (20 IU, n = 43; 40 IU, n = 22) did not differ on key demographics. MDMA effects — physiological: MDMA produced dose-dependent cardiovascular stimulation. Both 0.75 and 1.5 mg/kg significantly increased heart rate, systolic and diastolic blood pressure versus placebo (reported F[2,1300] range 114.9–230.9, p < 0.001), and the 1.5 mg/kg dose produced larger increases than the 0.75 mg/kg dose (p < 0.001). Peak cardiovascular responses occurred between 90 and 120 minutes after capsule ingestion. MDMA effects — subjective and ESQ: MDMA robustly increased self-reported drug effects and several mood items. Both doses raised ratings of 'Feel Drug', 'Friendly' and 'Insightful' relative to placebo (reported F[2,1300] range 74.7–323.4, p < 0.001), with larger effects at 1.5 mg/kg. Peak subjective effects occurred around 60–120 minutes. MDMA also increased some negative ratings (for example, 'Anxious' and 'Lonely'). On the ESQ, desire to take the drug again increased dose-dependently. MDMA effects — behavioural: On the Morphed Facial Expression Task the higher MDMA dose (1.5 mg/kg) significantly reduced accuracy identifying angry and fearful faces (F[2,128] = 5.1, p < 0.01), while identification of happy and sad faces was not significantly affected. MDMA did not change ratings on the Social Evaluation Task. In the Social Choice Task, participants reported greater desire to engage in the social activity after the larger MDMA dose, while desire for solitary activities was unchanged (p < 0.05). Oxytocin effects: Neither oxytocin dose (20 or 40 IU) altered heart rate or blood pressure compared with placebo (reported in a supplementary table). Intranasal oxytocin produced small but statistically significant increases on some self-reported prosocial items; both doses increased ratings of 'Friendly' and 'Elated' relative to placebo, and the lower dose tended to show larger subjective effects, consistent with a non-linear dose response. The extracted results text for oxytocin behavioural effects is limited, but the Discussion reports that 40 IU enhanced recognition of negative emotional faces and that this improvement was observed only in women. Correlations between MDMA and oxytocin responses: Partial correlational analyses using AUC scores showed modest relationships for the lower oxytocin dose only. 'Insightful' ratings after 20 IU oxytocin correlated with 'Insightful' ratings after both MDMA doses (r = 0.38 and r = 0.37 for 0.75 and 1.5 mg/kg, respectively). 'Playful' ratings after 20 IU oxytocin correlated with 'Playful' after 1.5 mg/kg MDMA (r = 0.31). No significant correlations were observed for the 40 IU oxytocin group, which led the investigators to caution that some 20-IU correlations may be spurious.

Kirkpatrick and colleagues interpreted the findings as confirming and extending prior reports that MDMA produces acute prosocial effects. The investigators emphasised that MDMA dose-dependently increased subjective sociability and positive mood-related ratings and, at the higher dose, increased preference for a social activity. Behaviourally, the larger MDMA dose impaired recognition of negative facial expressions (anger and fear), which the authors suggest could contribute to increased sociability by reducing sensitivity to cues of social threat. By contrast, intranasal oxytocin produced only modest increases in selected self-reported sociability items and a distinct behavioural profile: the higher oxytocin dose (40 IU) enhanced recognition of negative emotional faces, and the lower oxytocin dose (20 IU) produced proportionally larger subjective effects on some items. The limited correlations between MDMA- and oxytocin-induced prosocial responses led the investigators to conclude that the prosocial effects of MDMA are not fully accounted for by oxytocin alone. They noted physiological differences consistent with distinct mechanisms: MDMA increased heart rate, blood pressure and some anxiety ratings, whereas oxytocin did not affect cardiovascular measures and the lower oxytocin dose reduced anxiety. The authors discussed plausible mechanistic explanations: MDMA causes widespread monoamine release (serotonin, dopamine, noradrenaline) and also appears to raise peripheral oxytocin, whereas oxytocin acts via oxytocin receptors and may have more targeted neuromodulatory effects. They highlighted uncertainty about the relationship between peripheral and central oxytocin levels and stated that differences in plasma or brain peptide concentrations could underlie the distinct effects observed. The investigators acknowledged several limitations: behavioural measures might not have been timed optimally to capture oxytocin effects (for example, the Social Choice Task occurred 2 h after nasal spray), the placebo and oxytocin nasal formulations differed slightly which could affect expectations, the sample comprised young adult MDMA users which may limit generalisability, and dose and route differences complicate direct comparison of the two agents. For implications, the authors suggested that MDMA's combined subjective and behavioural profile might help explain its therapeutic potential in contexts such as PTSD, by increasing engagement with a therapist and altering processing of negative emotions. They cautioned, however, that oxytocin is unlikely to be the sole mediator of MDMA's prosocial effects and pointed to future directions including testing combined sub-threshold doses and studying effects in more naturalistic social contexts or using more sensitive physiological and psychophysiological measures.