Pinpoint Pupils: Which Drugs Cause Constricted Pupils and Why

What Are Pinpoint Pupils?

Pinpoint pupils (miosis) describe pupils constricted to 2 mm or less, even in dim lighting. Normal pupil diameter ranges from 2 to 4 mm in bright light and 4 to 8 mm in dim light. When pupils remain constricted regardless of lighting conditions, something is overriding the normal pupillary response.

In emergency medicine, pinpoint pupils are one of the fastest indicators that a patient may have ingested opioids. But the sign is not exclusive to opioids.

Drugs That Cause Pinpoint Pupils

Opioids (Most Common Cause)

All opioids cause miosis by stimulating the parasympathetic nucleus of the oculomotor nerve (Edinger-Westphal nucleus). This includes:

• Heroin
• Fentanyl and carfentanil
• Oxycodone (OxyContin, Percocet)
• Hydrocodone (Vicodin, Norco)
• Morphine
• Codeine
• Methadone
• Buprenorphine (Suboxone)
• Tramadol

Opioid-induced miosis is dose-dependent. Higher doses produce smaller pupils. The effect persists as long as the drug is active. Tolerance to miosis develops partially with chronic use, meaning long-term opioid users may have somewhat larger pupils than acute users.

Cholinergic Medications

Drugs that stimulate the parasympathetic nervous system cause pupil constriction:

• Pilocarpine (glaucoma eye drops)
• Bethanechol
• Donepezil (Aricept, used for Alzheimer’s)

Clonidine

This alpha-2 agonist, used for blood pressure and ADHD, causes pinpoint pupils at therapeutic and toxic doses. Clonidine overdose mimics opioid overdose (pinpoint pupils, sedation, slow breathing).

Certain Antipsychotics

Some antipsychotic medications (olanzapine, quetiapine) can cause mild pupil constriction as a side effect.

A 2019 guideline from the American College of Emergency Physicians states: “Bilateral miotic pupils in an unresponsive patient should be treated presumptively as opioid overdose with naloxone administration, regardless of other potential causes. The risk of delayed treatment in actual opioid overdose outweighs the risk of naloxone in non-opioid cases.”

Medical Causes of Pinpoint Pupils

• Horner syndrome: Damage to the sympathetic nerve pathway (from stroke, tumor, or trauma) causes miosis on one side only, along with drooping eyelid (ptosis) and decreased sweating on the affected side.
• Pontine hemorrhage: Bleeding in the pons (brainstem) causes bilateral pinpoint pupils, coma, and loss of horizontal eye movements. This is a neurological emergency.
• Organophosphate poisoning: Insecticide exposure causes pinpoint pupils, excessive salivation, tearing, urination, and respiratory distress (the SLUDGE mnemonic).
• Iritis/Uveitis: Inflammation inside the eye can cause the pupil to constrict and become irregularly shaped.
• Bright light exposure: Normal physiological response. Both pupils constrict equally and respond to light changes.

Pinpoint Pupils in Overdose

In the context of suspected opioid overdose, look for the opioid triad:

1. Pinpoint pupils
2. Respiratory depression (slow, shallow, or absent breathing)
3. Decreased level of consciousness (unresponsive, cannot be woken)

This triad is a medical emergency. Act immediately:

1. Call 911.
2. Administer naloxone (Narcan) if available. Nasal spray: one spray in one nostril. Repeat after 2 to 3 minutes if no response.
3. Begin rescue breathing if the person is not breathing adequately.
4. Place in recovery position (on their side) to prevent aspiration if they vomit.
5. Stay with the person until emergency services arrive.

How to Assess Pupils

To check pupil size and reactivity:

1. Look at the person’s eyes in normal room lighting. Note if pupils appear unusually small.
2. Shine a light (phone flashlight) into each eye. Normal pupils constrict from the light. Already-pinpoint pupils will not change further.
3. Compare both eyes. Unequal pupil sizes (anisocoria) suggest a different cause than opioids.

Getting Help

If you or someone you know is using opioids and you are concerned about dependence or overdose risk, resources are available. Naloxone (Narcan) is available without a prescription at most pharmacies. SAMHSA (1-800-662-4357) provides free, confidential treatment referrals 24/7.