α₁-Adrenergic receptors contribute to the acute effects of 3,4-methylenedioxymethamphetamine in humans

All 16 participants completed the four crossover sessions and were included in the analyses. MDMA alone produced the expected sympathomimetic and subjective profile: significant increases in systolic and diastolic blood pressure, heart rate, and core body temperature, together with stimulant and positive mood effects on the AMRS and increases on several VAS items (any drug effect, good drug effect, drug liking, drug high, stimulated). MDMA also raised plasma epinephrine and norepinephrine concentrations and increased the total adverse-effect complaint score at 3 and 24 hours; no severe adverse events occurred. Doxazosin modified several MDMA effects in a mixed pattern. It significantly attenuated the MDMA-induced increases in systolic and diastolic blood pressure (AUEC0–6h interaction), while doxazosin alone did not change blood pressure. Paradoxically, doxazosin enhanced the heart-rate elevation produced by MDMA (greater Emax/AUEC for heart rate under doxazosin+MDMA than placebo+MDMA). The α1 antagonist also reduced the MDMA-induced rise in core temperature to a moderate extent, reflected by a significant doxazosin × MDMA interaction for AUEC0–6h of temperature. On subjective measures, MDMA increased multiple AMRS subscales. Doxazosin produced a modest but statistically significant reduction in the AMRS heightened-mood subscale (AUEC0–6h interaction) and a near-significant reduction in self-reported activation; other mood subscales, the VAS measures of drug liking/high, and the 5D-ASC scores were not significantly altered by doxazosin. The total adverse-effect score after MDMA was unaffected by doxazosin. Common acute complaints after MDMA (with and without doxazosin) included lack of appetite, thirst, concentration difficulties, bruxism and sweating. Plasma catecholamine results showed that MDMA elevated circulating epinephrine and norepinephrine. Doxazosin did not change the MDMA-induced epinephrine increase, whereas norepinephrine levels were raised by both MDMA and doxazosin with additive effects, consistent with a reflex sympathetic response to α1 blockade. Pharmacokinetic analyses indicated that doxazosin did not change MDMA or HMMA Cmax, AUC0–6h or Tmax. Doxazosin produced a small reduction in plasma MDA concentrations (slight decreases in Cmax and AUC0–6h). Interindividual CYP2D6 activity, as measured by the dextromethorphan/dextrorphan urine ratio, correlated with MDMA and HMMA exposure: reduced CYP2D6 activity was associated with larger MDMA AUC0–6h (Spearman R s = 0.61, P < 0.01) and smaller HMMA AUC0–6h (R s = −0.57, P < 0.05).

Donzelli and colleagues interpret the data as evidence that α1-adrenergic receptors substantially mediate the blood-pressure effects of MDMA in humans and contribute, to a lesser extent, to the thermogenic response and some positive/stimulant subjective effects. The finding that doxazosin reduced MDMA-induced hypertension but enhanced MDMA-associated tachycardia is attributed to a compensatory, baroreceptor-mediated increase in sympathetic outflow and circulating norepinephrine following α1 blockade. The authors note that this pattern mirrors prior work in animals and humans showing that selective α1 blockade lowers pressure responses but can provoke reflex tachycardia. In relation to temperature regulation, the partial attenuation of MDMA-induced hyperthermia by doxazosin aligns with preclinical mechanisms in which α1-mediated peripheral vasoconstriction impairs heat dissipation, while other adrenergic mechanisms (and mitochondrial uncoupling) contribute to heat generation; combined adrenergic antagonists such as carvedilol and labetalol have previously produced stronger reductions in MDMA hyperthermia. Regarding subjective effects, the authors place their findings in the context of prior pharmacological manipulations: serotonin transporter blockade has been most effective at reducing MDMA’s mood and perceptual effects, whereas interventions targeting norepinephrine release or α1 receptors produced more modest or selective reductions. In this study, doxazosin's effect on mood was weak and limited to the heightened-mood subscale; the investigators suggest that α1 stimulation may contribute to some positive and stimulant subjective effects but that serotoninergic mechanisms play the dominant role. Pharmacokinetic interactions were unlikely to explain the pharmacodynamic findings: doxazosin did not change MDMA or HMMA plasma levels and only slightly reduced MDA, a minor metabolite. Interindividual differences in CYP2D6 activity predicted MDMA and HMMA exposure, consistent with known metabolic pathways. The authors acknowledge several limitations: only single, relatively high doses of MDMA and doxazosin were tested, preventing dose–response assessment; doxazosin may have limited central nervous system penetration so central α1 occupancy might have been insufficient to alter some psychoactive effects; and multiple mood measures were used without statistical correction for multiple comparisons, increasing the risk of type I error. They conclude that α1-adrenergic receptors contribute importantly to MDMA-induced hypertension and partially to thermogenic and possibly subjective effects, but that further work is needed to clarify central versus peripheral mechanisms and dose-dependent relationships.