April 24, 2023

What Drugs Cause Dilated Pupils?

Learn what drugs can cause dilated pupils, or mydriasis, and what you can do about suspected drug use.

dilated pupils

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Table of Contents

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Susana Spiegel

Recovery Writer and Advocate

Last Update on June 11, 2024

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Dilated pupils, medically known as Mydriasis, can result from various factors, including certain drugs that impact the nervous system. This article will explore dilated pupils and provide an overview of the drugs that can lead to this condition.

Understanding Dilated Pupils (Mydriasis)

Mydriasis is the abnormal dilation of the pupils in response to various stimuli, such as specific drugs. Normally, the size of the pupils is controlled by the iris sphincter muscle, which contracts or relaxes to adjust the amount of light entering the eye. When the iris sphincter muscle relaxes, more light than usual enters the eye, resulting in dilated pupils. This dilation can cause increased sensitivity to light, blurred vision, and noticeable eye appearance changes.

Drugs That Can Cause Pupil Dilation

Various drugs can cause pupil dilation due to their effects on the nervous system. These substances typically belong to categories like stimulants, hallucinogens, and anticholinergic drugs. In some cases, pupil dilation is an unintended side effect resulting from a drug’s impact on the body’s physiological systems.

Let’s look at the various drugs known to cause dilated pupils.

normal pupil example
Normal Pupil Example
what drugs cause dilated pupils
Dilated Pupil (Mydriasis) Example
Anisocoria Pupil Example
Miosis Constricted Pupils Example
Constricted Pupils (Miosis) Example
A Normal pupil is the dark, circular opening in the center of the iris that controls the amount of light entering the eye. In normal conditions, both pupils should be equal in size and constrict (get smaller) in bright light and dilate (get larger) in dim light. The typical diameter of a pupil in normal light is between 2 and 4 millimeters (mm), but it can range from 1 mm in bright light to 8 mm in the dark. Pupils that are equal in size, round, and reactive to light are generally considered normal and healthy.


Stimulants are a class of drugs that increase activity in the central nervous system, leading to heightened alertness, increased energy, and elevated mood. Due to their stimulating effects, stimulants often cause pupil dilation.

Amphetamines are synthetic stimulants that affect the release and reuptake of neurotransmitters in the brain, including dopamine, norepinephrine, and serotonin. They can cause increased heart rate, elevated blood pressure, and dilated pupils.
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Hallucinogens are psychoactive substances that can alter perception, thoughts, and emotions by affecting the brain’s serotonin receptors. These drugs often cause dilated pupils as part of their effects on the nervous system.
LSD is a potent hallucinogenic drug derived from the ergot fungus. It primarily affects serotonin receptors in the brain, leading to altered perceptions, vivid hallucinations, and a distorted sense of time. LSD commonly causes dilated pupils and other side effects like elevated body temperature, increased heart rate, and sweating.

Quick Tip

Be Aware of Drug Interactions

When using prescription or over-the-counter medications, it’s essential to be aware of potential drug interactions that can affect pupil size. Some medications, such as antihistamines, decongestants, or antidepressants, can cause pupil dilation or constriction when combined with other substances. Always consult with your healthcare provider or pharmacist before taking any new medications, and inform them of any recreational drug use to avoid potentially dangerous interactions.
Yes, pupil dilation caused by drug use can be dangerous. Dilated pupils can cause increased sensitivity to light, blurred vision, and difficulty focusing. Sometimes, prolonged pupil dilation can lead to more serious eye problems, such as angle-closure glaucoma or retinal damage.
The duration of drug-induced pupil dilation varies depending on the specific drug and the individual’s metabolism. Generally, pupil dilation from stimulants like cocaine or MDMA can last for several hours, while the effects of hallucinogens like LSD may persist for up to 12 hours or more. Some anticholinergic drugs can cause pupil dilation that lasts for several days.
While pupil dilation or constriction can be a sign of drug use, healthcare professionals cannot definitively determine if someone has used drugs based on pupil size alone. Other factors, such as certain medical conditions, brain injuries, or even natural variations in pupil size, can cause similar pupil changes. However, when combined with other physical symptoms and patient history, pupil size can be an important factor in identifying potential drug use.

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Opiates and Opioids

Opiates and opioids act on opioid receptors in the brain and central nervous system, providing pain relief and producing relaxation and euphoria. While these substances are known for constricting the pupils (miosis), they can sometimes lead to dilated pupils under certain circumstances or during withdrawal.

Heroin is an illegal and highly addictive opioid derived from morphine, which comes from opium poppy plants. It is a potent analgesic that induces intense relaxation and euphoria. Although heroin typically causes pinpoint pupils (miosis), dilated pupils can occur during withdrawal or as a result of an overdose, which can lead to severe health consequences, including respiratory failure and death.

Recap of Drugs Causing Dilated Pupils

We’ve explored various drugs that can cause mydriasis or dilated pupils. These substances include:

  • Stimulants like amphetamines, cocaine, and high doses of caffeine
  • Hallucinogens such as LSD, psilocybin, mescaline, and DMT
  • Opioids like heroin, morphine, oxycodone, and fentanyl in cases of overdose or withdrawal

The extent of pupil dilation and specific side effects experienced may vary depending on factors such as the type of drug, dosage, individual sensitivity, and duration of use.

Helping Someone with Suspected Drug Use

If you suspect someone you know may be under the influence of drugs due to dilated pupils, it’s essential to approach the situation with care and empathy. Your response can be critical in helping them seek support and preventing more severe consequences. Consider these steps:

  1.  Observe and assess the situation: Take note of their behavior and other signs that might indicate drug use, like slurred speech, unsteady gait, or erratic behavior.
  2. Approach with care and empathy: Choose your words carefully and find a private, comfortable place to talk. Express your concern for their well-being and ask open-ended questions to encourage them to share their experience.
  3. Offer support and resources: If they admit to using drugs, offer your support and help them explore available resources like professional help, local support groups, mental health services, or addiction treatment programs.
  4. Recognize the limitations of your role: Understand that you cannot force someone to change their behavior or seek help if they are not ready. Provide support and encouragement, but know that your role is limited.
  5. Monitor the situation and prioritize safety: Call emergency services immediately if you believe they may be in immediate danger or suspect an overdose. Signs of potential overdose include extreme drowsiness, difficulty breathing, seizures, or loss of consciousness.
  6. Maintain communication and follow-up: Continue to check in with the person and offer your support. Keep an open line of communication and be available to listen, encourage, and share resources as needed.

Key Takeaways

How Drugs Affect Pupil Size

The impact of drug use on pupil dilation is a multifaceted issue. Different substances lead to unique changes in pupil size and function. From the widespread mydriasis caused by stimulants to the less common anisocoria induced by certain medications, these variations in pupil size can provide essential insights for healthcare professionals and concerned loved ones.

Pupil dilation is just one aspect of identifying drug use. While it can be a significant indicator, it must be considered with other symptoms and a thorough patient history to create a comprehensive understanding. By raising awareness about the dangers associated with drug use and the potential interactions between various substances, we can work together to create a safer, healthier community for all.

If you or someone close to you is grappling with substance abuse, know that you are not alone in this challenge. Cornerstone Healing Center offers compassionate, evidence-based care to help individuals overcome addiction and reclaim their lives. Our committed team of healthcare professionals supports you at every step of your journey, providing personalized treatment plans, a wide array of therapeutic approaches, and a judgment-free environment that places your well-being at the forefront. Remember that recovery is within reach, and we are here to guide you toward a brighter, drug-free future.

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Author & Reviewers

susana spiegel recovery writer and SEO expert

Susana is a recovery writer and advocate with over 8 years in addiction recovery. She is passionate about sharing accurate and helpful information about mental health, addiction, and recovery. She holds a Bachelor’s in Christian Studies from Grand Canyon University and has over 7 years of working in the addiction field. 

lionel estrada lisac clinical director

Lionel is the Clinical Director of Cornerstone’s Scottsdale treatment facilities. He has had over 4 years at Cornerstone. He is personally in recovery and passionate about helping others overcome substance abuse and mental health challenges; he is trained as an EMDR, adopting a trauma-informed approach to treat the underlying issues.

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