Updated on April 3, 2024
5 min read

Does Drug Use Cause Dilated Pupils?

Why Do Certain Drugs Cause Dilated Pupils?

The iris is the part of the eye with muscles that manipulate the pupils. Some drugs can relax our muscles, including the iris, causing the pupils to dilate.6

Another reason why some drugs cause dilated pupils is the interference with neurotransmitters. Neurotransmitters are the brain's chemical messengers that affect how your brain communicates with other parts of the body.

Some drugs are known to slow down these neurotransmitters, which can affect how the brain communicates with the iris. Because of this, your iris will react to lighting changes much slower.

What Drugs Cause Dilated Pupils?

Apart from prescription medications, commonly misused drugs also affect pupil size. This is because they affect the normal bodily functions of the iris. 

Enlarged pupils can indicate intoxication, drug use, and drug addiction.2 Drugs that can cause pupil dilation include:

What Medications Cause Dilated Pupils? 

Over-the-counter drugs and prescription medication can interfere with the brain’s chemical messengers or neurotransmitters. These include:

What Should You Avoid If You Have Dilated Pupils?

To avoid permanent damage from dilated pupils, be careful about how you care for your eyes. If you notice you have dilated pupils, consider taking some of the below precautions: 

  • Avoid reading or focusing on smaller fonts
  • Don’t drive
  • Avoid direct sunlight

You should also consider reaching out to your optometrist. If certain drugs cause your pupils to dilate, consult your healthcare professional for other treatment options.

When to Seek Medical Assistance

Even after following the above precautions, pupil dilation can be serious and require further medical attention. You should seek medical assistance if you’ve experienced the following:

  • Your pupils are dilated without any clear reason
  • Eye dilation after a traumatic head injury or an eye injury
  • One pupil is larger than the other after pupil dilation has subsided
  • Your prescription medication is causing your eyes to dilate

If you notice a family member’s pupils are unusually dilated from suspected drug use, it’s important to take action. Consider a professional intervention.

How Long Does it Take Pupils to Undilate After Drug Use?

The duration of pupil dilation depends on the cause. 

Pupil dilation from eye drops used for an eye exam can last up to 4 to 6 hours. Some people might take longer than usual for the effects to wear off, especially those with lighter-colored eyes.7 

On the other hand, pupil dilation caused by medications or drugs may persist until the effect of the drug wears off. It can be impossible to tell precisely how long the dilation effects will last since people react differently to various medications.


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Can Alcohol Dilate Your Pupils?

Alcohol causes every muscle in the body to relax, including the iris muscles. This causes the pupils to dilate and constrict. A person intoxicated with alcohol will experience slower pupil dilation and constriction.5 

Slow pupil reaction related to alcohol use is why people are often advised against drunk driving. It affects an intoxicated person's response to oncoming headlights, which can be dangerous.

The pupil dilation due to alcohol intake is only temporary. This means that alcohol will only affect the pupils when someone is intoxicated.

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Short-Term Side Effects of Dilated Pupils

Whether you have dilated pupils because of an eye exam or drug use, you’ll experience some short-term side effects. These side effects are caused by your eyes trying to adjust to the lighting conditions through constriction.9

Possible short-term side effects include:

  • Blurry vision
  • Migraines
  • Trouble focusing on close objects
  • Eye pain
  • Watery eyes
  • Light sensitivity

Can Dilated Pupils Cause Permanent Side Effects? 

Unfortunately, dilated pupils can cause permanent side effects if you aren’t careful. If you expose your eyes to lots of sunlight when your eyes are dilated, you might experience permanent UV light damage.8

If you have to be under the sun after your pupils have dilated, keep your eyes away from direct sunlight. Fortunately, there are ways to help you avoid bright light.

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How to Manage Dilated Pupils

Dilated pupils will react slower to lighting changes. Because of this, your eyes will be more sensitive to bright light.

Here are a few things you can use to protect your eyes from bright lights or the sun:

  • Photochromic lenses: These prescription lenses will darken when you go outside to protect your eyes
  • Polarized lenses: Polarized lenses block the glare from sunlight reflected off light-colored surfaces
  • Custom contact lenses: Custom-made contact lenses can mask the appearance of dilated pupils, which can be helpful for people with permanently dilated pupils

If your pupils are dilated for a more extended period, like in the effects of dilation eye drops, your optometrist will recommend some sunglasses you can use.

What Causes Pupil Dilation?

Your pupils naturally dilate depending on your exposure to light. When the light is too bright, your pupils will constrict to minimize the amount getting into your eyes and dilate in dim light. 

However, the light factor isn’t the only element that can affect pupil dilation. Other factors that can cause pupil dilation include:1

  • Color and distance
  • Brain or eye injury
  • Medications
  • Drug use
  • Sexual arousal (increased oxytocin hormone)
  • Health conditions (Holmes-Adie syndrome, congenital aniridia, and mydriasis)


Pupil dilation is typically caused by lighting changes. However, certain factors can cause your pupils to dilate, this includes:

  • Medication
  • Drug use
  • Brain or eye injury
  • Sexual arousal
  • Health conditions 

There are some short-term side effects of pupil dilation. However, it can cause permanent damage if you’re not careful.

If you’re experiencing pupil dilation, consider speaking to an optometrist, especially if they’re dilated for an extended period. They may recommend sunglasses that you can use to protect your eyes.

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Updated on April 3, 2024
11 sources cited
Updated on April 3, 2024
  1. The pupils are the windows to sexuality: pupil dilation as a visual cue to others’ sexual interest,” Journal of Evolution and Human Behavior, 2015.
  2. Cocaine DrugFacts,” National Institute of Health (NIH)
  3. Lysergic Acid Diethylamide (LSD),” National Center for Biotechnology Information (NCBI), 2021.
  4. Amphetamines” United States Drug Enforcement Administration (DEA)
  5. Effect of glare on night time driving in alcoholic versus non-alcoholic professional drivers,” International Journal of Applied and Basic Medical Research, 2013.
  6. Clinical Methods: The History, Physical, and Laboratory Examinations,” National Center for Biotechnology Information (NCBI).
  7. Dilating Eye Drops,”  American Association for Pediatric Ophthalmology & Strabismus, 2020.
  8. Tips for Choosing the Best Sunglasses,” American Academy of Ophthalmology, 2021.
  9. Mathôt, S. “Pupillometry: Psychology, Physiology, and Function.” Journal of cognition, 2018.

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