Fig. 1. Acute subjective effects of 100 µg lysergic acid diethylamide (LSD), 100 mg 3,4-methylenedioxymethamphetamine (MDMA), and the LSD + MDMA combination over time on the Visual Analog Scale (VAS).

LSD and the LSD + MDMA combination produced comparable subjective effects with no significant differences in E_max values (Table 1). However, the co-administration of MDMA and LSD prolonged the psychedelic experience compared with LSD alone (Supplementary Table S5). Overall, effects of LSD and LSD + MDMA were significantly stronger and longer compared with MDMA alone. There was no significant difference in peak “drug high” between the substances alone and the combination. The substances were administered at t = 0 h. The data are expressed as the mean ± SEM percentage of maximally possible scores in 24 subjects. The corresponding maximal responses and statistics are shown in Table 1.