What Drugs Cause Dilated Pupils?

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Close-up of an eye with dilated pupil indicative of possible drug use

Pupil dilation, a noticeable enlargement of the dark center of the eye, is a common physiological reaction that can be influenced by a variety of factors, including drug use. Understanding what drugs cause dilated pupils is crucial for both medical professionals and the general public.

Why Does Pupil Dilation Occur?

Pupil dilation, medically known as mydriasis, can occur due to natural causes like changes in light or emotional states. However, it can also be a side effect of certain drugs. This dilation happens when the muscles in the iris of the eye either relax or contract to let more light into the eye. In the context of drug use, pupil dilation is often a result of the drug’s effect on the body’s nervous system.

Drugs Associated with Pupil Dilation

Several drugs are known to cause dilated pupils, including both legal prescription medications and illegal substances. Understanding these drugs and their effects on the eye can be important for identifying potential drug use or abuse.


Stimulants like cocaine, amphetamines, and methamphetamine can cause significant pupil dilation. These substances increase neural activity, leading to an excited state that often reflects in the eyes.


Hallucinogenic drugs, such as LSD and psilocybin mushrooms, also cause pupils to dilate. These drugs alter perception and can intensify sensory experiences, including visual ones.


Although opioids like heroin and morphine typically cause pupils to constrict, they can sometimes lead to dilation depending on dosage and individual reactions.

Prescription Medications

Certain prescription drugs, including some antidepressants, antihistamines, and decongestants, can also lead to pupil dilation. This is often a side effect of the medication’s impact on the nervous system.


Cannabis, though known for its relaxing effects, can also cause pupil dilation due to its psychoactive properties.

Other Effects of Drug Use on the Body

Apart from pupil dilation, drug use can have various effects on the body, including changes in heart rate, blood pressure, and mental state. These effects vary greatly depending on the type and amount of drug used.


Recognizing the signs of drug use, including dilated pupils, is important for both personal health and public safety. If you suspect someone is using drugs, it’s important to approach the situation with understanding and seek professional help if necessary.