What drugs cause dilated pupils?
Dilated pupils are characterized by an enlargement of the black center portion of the eye, and serve as one of the most recognizable physical indicators of drug use. This physiological response provides valuable information to medical professionals and concerned individuals alike.
Understanding what drugs dilate pupils can help identify potential substance abuse and distinguish between recreational drug use, prescription medication effects, and other medical conditions that may result in similar symptoms.
How Different Drugs Cause Pupil Dilation
Many drugs, both illicit and prescription, cause pupil dilation (mydriasis) by interfering with the nervous system’s control over the iris muscles. This is a direct consequence of chemical actions on neurotransmitters and receptors in the eye and brain. Medications that cause mydriasis may do so in unique ways. For example, stimulants like amphetamines cause large pupils by increasing norepinephrine and dopamine. Other medications, like anticholinergic agents, dilate the pupils by blocking acetylcholine at the iris sphincter which prevents constriction.
Recreational and Illicit Drugs That Cause Dilated Pupils
Numerous recreational and illicit substances cause noticeable pupil dilation. These drugs primarily fall into the categories of stimulants and hallucinogens, though other classes of drugs may produce similar effects.
Stimulants
Stimulant drugs consistently cause pupil dilation by activating the sympathetic nervous system, essentially triggering a sustained "fight or flight" response. Common stimulants that dilate pupils include:
- Cocaine and crack cocaine, which produce rapid and pronounced mydriasis
- Amphetamines, including street forms and pharmaceutical variants
- Methamphetamine (crystal meth), which causes extreme dilation often accompanied by other visible symptoms
- MDMA (ecstasy), a stimulant with hallucinogenic properties that reliably dilates pupils
Hallucinogens
Hallucinogenic substances typically produce significant pupil dilation, often more pronounced than stimulants. These include:
- LSD (lysergic acid diethylamide), which causes marked dilation that can last for several hours
- Psilocybin (found in "magic mushrooms"), producing moderate to significant mydriasis
- Mescaline, a naturally occurring psychedelic compound found in certain cacti
Other Recreational Substances
Several other categories of recreational drugs can cause dilated pupils:
- Ketamine, a dissociative anesthetic that produces moderate pupil dilation
- Bath salts, synthetic cathinones that mimic the effects of stimulants
- Cannabis, which may cause mild to moderate dilation in some users
- Inhalants, which can affect pupil size through their impact on the central nervous system
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Prescription and Over-the-Counter Medications
Many legitimate medications can also cause dilated pupils as a side effect. Patients taking these medications under medical supervision should be aware of this potential effect but need not be concerned unless experiencing discomfort or vision problems.
Antidepressants
Selective serotonin reuptake inhibitors (SSRIs) and other antidepressant medications often cause pupil dilation due to their effects on serotonin levels in the brain. Tricyclic antidepressants are thought to cause pupil dilation due to their anticholinergic effects. This side effect is generally mild to moderate and may diminish over time as the body adjusts to the medication.
Other Prescription Medications
Additional prescription drugs that may cause mydriasis include:
- Antihistamines, particularly first-generation variants
- Benzodiazepines, prescribed for anxiety and sleep disorders
- Stimulant medications used to treat ADHD, such as methylphenidate (Ritalin) and amphetamine salts (Adderall)
- Anticholinergic medications used for various conditions including overactive bladder and Parkinson's disease
Mydriatic Medications
Eye doctors frequently use mydriatic eye drops specifically designed to dilate pupils during comprehensive eye examinations. These medications, including tropicamide and phenylephrine, temporarily block the muscles that constrict the pupil, allowing for improved visualization of the internal structures of the eye. This medically-induced dilation typically lasts for several hours before gradually returning to normal.
Conclusion
Dilated pupils frequently occur as a physiological response to various substances, ranging from illicit drugs like cocaine, LSD, and ecstasy to prescription medications including antidepressants and antihistamines. This dilation results from the drug's effects on the parasympathetic and sympathetic nervous systems, which control the muscles responsible for adjusting pupil size.
For individuals concerned about drug use in themselves or others, understanding these physiological responses provides one tool among many for identifying potential problems and seeking appropriate support. If substance abuse is suspected, consulting with healthcare professionals can help determine appropriate next steps and treatment options.
References
- Constable, P. A., et. al. 2022. A Review of Ocular Complications Associated with Medications Used for Anxiety, Depression, and Stress. In: Clinical Optometry. DOI: https://doi.org/10.2147/OPTO.S355091
- Dhingra, D., et. al. 2017 Illicit drugs: Effects on eye. In: Indian J Med Res. DOI: https://doi.org/10.4103/ijmr.IJMR_1210_17
- MedlinePlus. 2024. Substance use - inhalants. Accessed April 9, 2025 at https://medlineplus.gov/ency/patientinstructions/000794.htm#
- Mukamal, R. 2023. Concerned About Dilated Pupils? Causes and Treatment. American Academy of Opthalmology. Accessed April 9, 2025 at https://www.aao.org/eye-health/tips-prevention/dilated-pupils-causes-worry-concerned-treatment
- United States Drug Enforcement Administration. n.d. Ketamine. Accessed April 9, 2025 at https://www.dea.gov/factsheets/ketamine
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