Illegal Drugs That Cause Dilated Pupils (Mydriasis)
Amphetamines (including methamphetamine and lisdexamphetamine) and cocaine are the primary illegal drugs that cause dilated pupils through sympathomimetic stimulation. 1
Primary Offending Substances
Stimulants (Most Common)
- Amphetamines/Methamphetamine: Produce marked pupillary dilation that persists for at least 5 hours after use through both peripheral sympathetic activation and central mechanisms 1, 2
- Lisdexamphetamine (70 mg dose): Causes significant mydriasis (p < 0.001) regardless of ambient light conditions, with effects lasting beyond 5 hours 1
- Cocaine: Similar sympathomimetic effects causing pronounced pupillary dilation
Mechanism of Action
These stimulants work through:
- Direct sympathetic nervous system activation (alpha-adrenergic stimulation)
- Central inhibition of the oculomotor nucleus (parasympathetic disruption)
- Dopaminergic pathways may contribute, though the exact role remains unclear 2
Important Clinical Distinctions
Drugs That Do NOT Cause Mydriasis
Be aware that other common illegal drugs have opposite effects:
- Opioids (heroin, illicit fentanyl): Cause miosis (pinpoint pupils), not mydriasis 1
- Cannabis/Marijuana: Causes miosis at peak effect (p = 0.05), along with conjunctival injection (red eyes) and reduced pupillary light reflex 1
Prescription Drugs with Abuse Potential
While not strictly "illegal," these commonly diverted substances cause mydriasis:
- Anticholinergic medications (when abused): Block parasympathetic tone causing dilation 3
- SSRIs (when diverted): Cause persistent mydriasis (mean pupil diameter 3.5mm vs 3.1mm in controls, p < 0.05) 4
Clinical Recognition Pattern
The duration and persistence of mydriasis helps identify the substance:
- Stimulant-induced mydriasis: Lasts 5+ hours and remains dilated even under bright light conditions 1
- Accompanied by other sympathomimetic signs: tachycardia, hypertension, agitation, stereotyped behaviors 2
- Pupils remain reactive to light (unlike anticholinergic toxicity where they become fixed)
Key Clinical Pitfall
Do not confuse stimulant mydriasis with angle-closure glaucoma. While the guidelines 3 extensively discuss medications that can precipitate angle closure through pupillary dilation (anticholinergics, adrenergics), stimulant-induced mydriasis in structurally normal eyes does not typically cause acute angle closure unless pre-existing anatomical risk factors exist (hyperopia, shallow anterior chamber, age >40).
The distinguishing features: angle-closure presents with severe eye pain, headache, nausea, corneal edema, and markedly elevated intraocular pressure—not just isolated mydriasis 3, 5.