Depressive mood ratings are reduced by MDMA in female polydrug ecstasy users homozygous for the l-allele of the serotonin transporter

MDMA acts primarily on the central serotonin (5-HT) system, with the serotonin transporter (SERT, encoded by SLC6A4) being a major target. Acute MDMA causes reverse transport of the reuptake transporter, elevating synaptic 5-HT, and reliably produces increases in positive affect (for example vigour, elation) as well as increases in some negative affective states (notably anxiety and confusion). A common functional polymorphism in the SERT promoter region (5-HTTLPR) exists as long (l) and short (s) alleles; the l-allele is associated with higher transporter expression and greater 5-HT uptake capacity than the s-allele. Previous literature has associated the s-allele with higher anxiety and negative mood and altered amygdala structure/function, but findings are not fully consistent and other factors such as methylation may modify effects. Kuypers and colleagues set out to test whether acute MDMA-induced mood effects differ by 5-HTTLPR genotype and by sex. Because individual placebo-controlled MDMA studies are typically underpowered for genotype comparisons, the investigators pooled data from four within-subject, placebo-controlled trials to examine whether carriers of the slow-working SERT variants (s-allele carriers) show different acute mood responses to MDMA (75 mg) than homozygous l-allele individuals, and whether any mood effects correlate with MDMA blood concentrations. The primary clinical question was whether genotype and sex moderate MDMA's acute effects on positive and negative mood states.

The analysis combined data from four double-blind, placebo-controlled, within-subject trials conducted at Maastricht University; each participant received oral MDMA 75 mg on one test day and placebo on another, with test days separated by at least 7 days. Participants were polydrug ecstasy users recruited under uniform inclusion/exclusion criteria: age 18–40, medically and psychiatrically healthy, free from medication, at least three prior experiences with ecstasy/MDMA, BMI 18–28 kg/m2, and for women exclusion of pregnancy/lactation. After screening for recent drug use and pregnancy, participants provided a blood sample for genotyping and a second sample 90 minutes after treatment for MDMA plasma measurement. Mood was assessed using the Profile of Mood States (POMS) approximately 90 minutes post-dose. Genotyping was carried out on DNA from peripheral blood leukocytes using a bi-allelic 5-HTTLPR assay; participants were grouped into an l-group (homozygous l/l) and an s-group (s/l or s/s). MDMA concentrations in plasma were measured by gas chromatography–mass spectrometry. The pooled sample initially comprised 72 ecstasy users, but missing genotyping data reduced the analysed sample to N = 63; the Discussion reports a sample distribution of roughly 76.2% s-group and 23.8% l-group (≈48 s-group, 15 l-group). Statistical analysis used repeated-measures general linear models (GLM) with Treatment (MDMA vs placebo) as the within-subject factor and Genotype (s-group vs l-group) and Sex as between-subject factors. Where interaction effects were found, difference scores (MDMA minus placebo) were analysed using univariate GLM. MDMA concentration data were analysed with ANOVA with Sex and Genotype as between-subject factors. Pearson correlations were computed between POMS scales and MDMA concentrations. The nominal alpha was set at p = 0.05 (uncorrected) and partial eta-squared (ƞp2) reported as effect size.

After pooling, the final analysed sample comprised N = 63 polydrug ecstasy users, with the s-group being the majority. On positive mood scales, MDMA produced robust main effects: participants reported greater vigour (F1,59 = 18.21, p < 0.001, ƞp2 = 0.24), friendliness (F1,59 = 6.01, p = 0.02, ƞp2 = 0.09), elation (F1,59 = 20.71, p < 0.001, ƞp2 = 0.26), arousal (F1,59 = 16.33, p < 0.001, ƞp2 = 0.22) and overall positive mood (F1,59 = 15.77, p < 0.001, ƞp2 = 0.21). There were no significant effects of Sex, Genotype, nor interactions involving these factors on the positive mood scales. For negative affect, MDMA increased self-reported anxiety (F1,59 = 31.82, p < 0.001, ƞp2 = 0.35) and confusion (F1,59 = 12.41, p = 0.001, ƞp2 = 0.17). A main effect of Genotype emerged for anxiety, with the l-group reporting higher anxiety ratings than the s-group irrespective of treatment or sex (F1,59 = 7.29, p = 0.009, ƞp2 = 0.11). A three-way Treatment × Sex × Genotype interaction was observed for the POMS Depression scale (F1,59 = 5.56, p = 0.02, ƞp2 = 0.09). Follow-up univariate analyses indicated that the MDMA–placebo difference in depression ratings was significant in females (F1,39 = 4.76, p = 0.04, ƞp2 = 0.19) and approached significance in males (F1,39 = 3.78, p = 0.059, ƞp2 = 0.09). In the placebo condition, depression ratings differed between female s- and l-groups (F1,20 = 5.07, p = 0.04, ƞp2 = 0.20). The pattern reported suggests that MDMA reduced higher baseline depression ratings observed in female l-group participants; the opposite pattern (non-significant) was seen in males. No Treatment, Sex, Genotype, or interaction effects were found for Anger or Fatigue. Analyses of MDMA plasma concentrations did not demonstrate significant main effects of Sex, Genotype, or their interaction on measured MDMA levels. Pearson correlation analysis showed a modest positive relationship between MDMA concentration and anxiety ratings (r56 = 0.26, p = 0.05); no other POMS scales correlated significantly with plasma MDMA.

Kuypers and colleagues interpret the pooled findings as confirming that a single 75 mg dose of MDMA reliably increases positive mood while also elevating anxiety and confusion. Genotype generally did not moderate most acute mood effects, but there was a notable genotype-by-sex effect for self-rated depression: MDMA attenuated depression ratings specifically in females homozygous for the l-allele. The l-group also reported higher anxiety overall, independent of treatment or sex. The authors note that the depression finding is somewhat counterintuitive because prior studies often report higher anxiety and depression risk among s-allele carriers. They examined representativeness of their ecstasy user sample and report genotype frequencies similar to European population norms, arguing against gross sampling bias. Kuypers and colleagues also discuss potential biological moderators that could reconcile divergent findings in the literature, emphasising that methylation of the SERT promoter can alter associations between 5-HTTLPR genotype and psychological measures. They cite prior work indicating that MDMA can affect 5-HTT expression and methylation and that these effects might be more pronounced in women and in l/l carriers, which could plausibly contribute to the sex- and genotype-specific depression effect observed here. Several caveats are acknowledged. The authors highlight the small effect size of the interaction and a very small female l-group sample (fewer than 10 participants), warning that the result should be handled with caution and not over-interpreted. They further note methodological limitations: only a single MDMA dose was studied, bi-allelic rather than tri-allelic 5-HTTLPR classification was used (the tri-allelic form distinguishes lA and lG variants), and methylation status was not assessed. Regarding clinical implications, the investigators suggest that most acute emotional responses to MDMA appear independent of sex, 5-HTTLPR genotype and plasma MDMA concentrations, and therefore routine adjustment of treatment by genotype or sex may not be necessary; nonetheless they recommend replication in larger samples and the inclusion of tri-allelic genotyping and methylation measures in future studies.