Does MDMA cause mydriasis (dilated pupils)?

Does MDMA cause dilated pupils?

Yes—MDMA reliably causes mydriasis (dilated pupils). 1, 2, 3

• Most recent/highest-quality direct evidence: placebo-controlled pupillometry trials in healthy adults show MDMA produces clear mydriasis and impairs the pupillary light reflex, with effects paralleling plasma MDMA levels and lasting several hours 1.
• Consistent earlier randomized crossover human trials demonstrated significant pupil dilation with MDMA at typical recreational doses (75–125 mg), alongside tachycardia and hypertension 2, 3.

Clinical implications (morbidity/mortality/QOL):

• Mydriasis itself is usually benign, but in susceptible eyes a dilated pupil can precipitate angle-closure glaucoma; consider ocular risk if visual halos/eye pain occur in dark environments 4.
• If MDMA is combined with other serotonergic agents, watch for serotonin syndrome, in which mydriasis commonly appears alongside hyperthermia, agitation, and clonus; this carries meaningful morbidity/mortality risk and warrants urgent management 5.

Pitfalls:

• Do not confuse with substances that cause miosis (e.g., opioids, THC); MDMA causes dilation, not constriction 6.
• Adulterants (e.g., methamphetamine, cathinones) also cause mydriasis, so dilation cannot confirm pure MDMA exposure but remains expected with sympathomimetic/serotonergic stimulants 7.