A Comprehensive Guide to Which Drugs Give You Dilated Pupils?

October 11, 2025 •

3 min read

Over 100 million eye examinations involve pharmacologically-induced pupil dilation in the United States every year. This effect, known as mydriasis, is not limited to ophthalmology, with many recreational and prescription drugs capable of causing it, prompting the question: Which drugs give you dilated pupils?.

Quick Summary

Pupil dilation is a physiological response caused by various substances, including recreational drugs like stimulants and hallucinogens, and a range of prescription and over-the-counter medications that affect the autonomic nervous system.

Key Points

Sympathetic Activation: Stimulants like cocaine and methamphetamine cause pupils to dilate by activating the body's 'fight-or-flight' response.
Anticholinergic Blockade: Medications such as mydriatic eye drops and certain antidepressants cause dilation by blocking the nerves that constrict the pupil.
Hallucinogenic Effects: Substances like LSD and psilocybin mushrooms disrupt neurotransmitter balance, resulting in noticeable pupil dilation.
Common Medications: Many prescription and over-the-counter drugs, including decongestants and antihistamines, can cause mild to moderate mydriasis.
Vision Risks: Dilated pupils can cause light sensitivity and blurred vision, and in rare cases, increase the risk of glaucoma in susceptible individuals.
Serotonin Syndrome Warning: Dilated pupils can be a symptom of potentially serious serotonin syndrome, which is caused by excessive serotonin levels from certain drug combinations.

The Pharmacology Behind Dilated Pupils

Pupil size is controlled by the iris muscles, which are regulated by the sympathetic and parasympathetic branches of the autonomic nervous system (ANS). The sympathetic system's "fight-or-flight" response causes dilation through the release of norepinephrine and adrenaline, contracting the iris dilator muscles. Conversely, the parasympathetic system's "rest-and-digest" function causes constriction by releasing acetylcholine, contracting the iris sphincter muscles. Drugs that cause mydriasis either stimulate the sympathetic system or block the parasympathetic system's action, disrupting this balance.

Recreational and Illicit Drugs

Several recreational drugs are known to cause mydriasis, often more significantly than prescription medications.

Stimulants

Stimulants like cocaine/crack cocaine and amphetamines (e.g., methamphetamine, Adderall) cause significant dilation by increasing norepinephrine and dopamine levels, activating the sympathetic nervous system. MDMA (Ecstasy/Molly) also causes marked dilation by affecting serotonin, norepinephrine, and dopamine.

Hallucinogens

Hallucinogenic substances such as LSD, psilocybin (mushrooms), and mescaline typically induce mydriasis by acting on serotonin receptors.

Other Illicit Substances

Cannabis (marijuana) can cause mild to moderate dilation, while ketamine and bath salts (synthetic cathinones) are also known to cause pupil dilation.

Prescription and Over-the-Counter Medications

Many legally available medications can cause mydriasis as a side effect or therapeutic effect.

Anticholinergics

These drugs block acetylcholine, preventing pupil constriction. Examples include mydriatic eye drops like tropicamide and atropine used by eye doctors, as well as some medications for overactive bladder or COPD.

Antidepressants

Certain antidepressants can affect pupil size. SSRIs may cause mild to moderate dilation, while tricyclic antidepressants have anticholinergic effects that lead to mydriasis.

Other Medications

Antihistamines, particularly first-generation types like Benadryl, can have anticholinergic effects. Decongestants containing pseudoephedrine or phenylephrine can cause dilation by activating adrenergic receptors. Prescription stimulants for ADHD, such as Adderall and Ritalin, also cause mydriasis. Accidental systemic exposure to botulinum toxin (Botox) can lead to bilateral dilated pupils.

Understanding the Risks of Drug-Induced Mydriasis

While temporary dilation for eye exams is generally safe, drug-induced mydriasis from other sources can have adverse effects. Potential complications include photophobia (light sensitivity), blurred vision, and in individuals with narrow angles, an increased risk of acute angle-closure glaucoma. Dilated pupils can also be a symptom of serotonin syndrome, a serious condition caused by excessive serotonin levels from certain drug combinations.

Comparison of Mydriasis-Causing Drug Categories


Drug Category	Primary Mechanism of Action	Common Examples	Duration of Mydriasis
Stimulants	Increase norepinephrine/dopamine, activating sympathetic nervous system.	Cocaine, Methamphetamine, MDMA, Adderall.	Typically several hours, depending on dose and substance.
Hallucinogens	Affect serotonin receptors, disrupting neurotransmitter balance.	LSD, Psilocybin (Mushrooms), Mescaline.	Can last up to 12 hours or more.
Anticholinergics	Block acetylcholine, inhibiting parasympathetic constriction.	Atropine, Tropicamide (mydriatic eye drops).	Medically-induced typically several hours; overdose can last days.
Antidepressants	Alter serotonin and norepinephrine levels.	SSRIs (mild), Tricyclics (anticholinergic effect).	Varies, can be mild and diminish over time.
Decongestants	Activate alpha-adrenergic receptors.	Pseudoephedrine, Phenylephrine.	Variable; can be a mild side effect.

Conclusion: Recognizing Drug-Induced Dilation

Dilated pupils indicate how a substance is affecting the autonomic nervous system. Unlike natural pupil changes, drug-induced mydriasis is often more persistent and lacks normal light reactivity. It's crucial to distinguish this from other medical conditions. If drug-induced mydriasis is suspected, especially with other concerning symptoms, professional medical help is necessary. For pharmacologically-induced mydriasis, new treatments like phentolamine ophthalmic solution (Ryzumvi) can help reverse the effect faster.

For more detailed information on pharmacologic dilation of the pupil, refer to EyeWiki.

Frequently Asked Questions

The duration of drug-induced pupil dilation varies depending on the specific substance, the dosage, and individual factors. For stimulants, it may last several hours, while for hallucinogens, it can sometimes persist for 12 hours or more.

Yes, some over-the-counter medications, such as decongestants containing phenylephrine or pseudoephedrine and certain antihistamines like Benadryl, can cause mild to moderate pupil dilation as a side effect.

While dilated pupils themselves are not directly dangerous, the underlying drug effects can be. Dilation can cause photophobia and blurred vision, and if caused by recreational drug abuse, can be a sign of a larger health issue.

No, doctors cannot definitively diagnose drug use by looking at pupils alone, as many factors influence pupil size. However, it can serve as one piece of evidence alongside other symptoms and medical testing.

Dilated pupils (mydriasis) are abnormally large, while pinpoint pupils (miosis) are constricted to a tiny size. Dilated pupils are often caused by stimulants, whereas pinpoint pupils are typically associated with opioid use.

Yes, certain types of antidepressants, including SSRIs and tricyclic antidepressants, can cause pupil dilation as a side effect due to their effects on neurotransmitter systems in the brain.

Eye doctors use mydriatic eye drops to dilate pupils during an exam. The effect is temporary. Recently, new FDA-approved ophthalmic solutions like Ryzumvi can be used to speed up the reversal of pharmacologically-induced mydriasis.