Pupil dilation can happen for many reasons, but pupils dilate or shrink when they’re exposed to direct light. Pupils can dilate through internal and external conditions, such as drugs, or intense emotions such as staring into the eyes of a loved one. The muscles in the pupil contract to protect the eyes from too much light and to help people be able to focus on important subjects.

Whether it’s illegal or prescribed, drugs can have effects on the eyes by causing them to dilate pupils. Pupils dilate or become large when exposed to light or other stimuli. Substances can play a role in pupils dilating but it’s not always the case.

Dilated pupils are usually a sign of substance abuse, however, other factors should be considered when deciding why a person’s pupils are dilated. Since most addicts combine different substances for them to cause greater effects, the side effects of using certain substances correlate with one another. People under the influence are more likely to be involved in a roadside accident. Staging an intervention is a start for anyone who is in dire need of support.

What Drugs Cause Dilated Pupils?

Certain changes challenge the human body’s automatic systems, by either increasing or decreasing functioning. Thus, a normal outing can cause people to reel from the side effects. The most common drugs that cause dilated pupils are:

Alcohol

Since alcohol contains ethanol, the body reacts to the substance with mild to moderate symptoms. For example, ingesting large amounts of alcohol in one sitting can cause people to have blurry vision, dilated pupils, or varied night blindness. Ethanol can also be present in tears which affect the function of the eyes and helps them maintain wetness.

The thermal temperature of the eyes is a consistent indicator of intoxication. Alcohol is often taken with other substances to boost the high effect that such substances cause people to feel. With Discovery Institute, treatment options are available if you or a loved one is struggling with an alcohol use disorder.

Marijuana

The effects of smoked cannabinoids can usually be experienced within a few minutes and last from 1 to 3 hours. Such cannabinoids are stored in the fat cells and spread throughout the body.

Marijuana can cause visual impairments from mild hallucinations and visual impairment to slow reaction times. Red or glossy eyes are a common symptom of marijuana consumption but this can vary.

Cocaine

Cocaine is a narcotic that is usually paired with alcohol for the dual effect. When ingested orally, the effects of cocaine can begin within a few minutes and last up to half an hour.

Cocaine suppresses the reuptake of the hormone norepinephrine, a chemical messenger that sends signals throughout the body. Chronic cocaine users can experience other complications such as chronic red eyes, lesions, and ulcers.

Methamphetamines

Methamphetamines affect the dopamine receptors in the body, which hijacks the reward centerpiece of the brain by increasing production. Thus, methamphetamine users often have a larger-than-life sense of euphoria. The common symptoms of methamphetamine use are dilated pupils, anxiety, and aggression.

LSD and Psilocybin (Mushrooms)

Hallucinogens such as LSD, mescaline, and psilocybin can produce symptoms that include restlessness, sleep deprivation, and dilated pupils. The effects of these drugs can range from 6 hours to 12 hours depending on the intake. In popular culture, people often associate dilated pupils with the experience of ingesting one of these substances.

Opiates

According to the CDC, nearly 500,000 people died from overdoses involving opioids, including prescription and illicit opioids, from 1999-2019. Opiates have a series of variations, either used for medical purposes or for illicit means. Due to the stimulation of the opioid receptors, these substances decrease the velocity of pupil dilation when eyes are in contact with light.

The dilated pupil effect that opioids cause usually begins within 15 minutes of use and typically lasts for about one to three hours.

These variations of these substances could be morphine (natural), heroin (semi-synthetic), meperidine and methadone (synthetic), prescription opioids such as hydrocodone, oxycodone, pentazocine, or fentanyl.

MDMA

MDMA (methylenedioxymethamphetamine) is a drug that causes side effects such as pupil dilation, dry mouth, decreased appetite, and increased heart rate. If taken orally, the drug spreads through the bloodstream quickly. The users of this drug often describe feelings of great confidence, insightfulness, heightened senses, and communication.

Benzodiazepines

Benzodiazepines are short but fast-acting barbiturates that can be used to offset the side effects of withdrawal. In addition, benzodiazepines are often used with alcohol or other substances for their calming effects. Using benzos for their calming effects can make them lethal though.

Blurred vision and dilated pupils are common visual side effects of benzo use. These symptoms can also be signs of benzo overdose. Other possible symptoms of benzo overdose include decreased heart rate, drowsiness, slurred speech, and coma.

In addition, there are several prescribed drugs that cause dilated pupils:

  • Antihistamines, such as Benadryl or Unisom
  • Antiseizure drugs, Topamax for example
  • Decongestants, like Sudafed
  • Medication for Parkinson’s disease, such as Symmetrel or Sinemet
  • Medicine for heart or stomach conditions, Atropine for example

What Are The Effects of Drugs on The Eyes?

what drugs cause dilated pupils

Psychotropic drugs can affect the eyes in multiple different ways. For example, psychotropic drugs can cause eyes to become dry or red. Psychotropic drugs can also cause people to experience blurry vision or rapid eye movement.

Dilated pupils are a product of the actions of the parasympathetic nervous system that aims to keep the body stable. As a result, certain prescription drugs such as SSRI antidepressants and heart medication have been known to cause dilated pupils.

Since the muscles in the eyes contract or expand, psychotropic drugs manipulate the normal function of the pupil, although such manipulation is rarely permanent. Although dilated pupils are a tell-tale sign of substance abuse, it’s important to check to see if there are other bodily signs of substance abuse such as one’s temperature, breathing, and heart rate prior to diagnosing an individual. This is particularly necessary for medical professionals when dealing with drug overdoses. Since psychotropic substances alter the parasympathetic nervous system, expect changes to happen in normal functioning.

The parasympathetic nervous system plays an important role in the overall guidance of the human body. For example. the parasympathetic nervous system is responsible for making bodily duties occur such as one’s heart rate, pupil constriction, and digestion.

The parasympathetic activates when the body is in a relaxed state. The system is also critical for the production of urine, saliva, and mucus. Think of the parasympathetic nervous system as the company manager for these essential products.

What Does It Mean When Pupils Dilate?

Let’s say you’ve been feeling sick for the past couple of days and your body is sensitive. There you are, patiently sitting on the hospital bed. Your doctor asks you to cough, checks your blood pressure, and tops it off with a flashlight in your eyes. The light causes your pupils to shrink before going back to normal. Why is that happening?

The light passes through the cornea to the pupil before the iris controls the amount of light. Once it reaches the lens, the light becomes focused through the retina. Afterward, the information is registered to the back of the eye structure where it’s inverted. The optic nerve and visual cortex are responsible for interpreting and displaying the image for you to view.

A good visual metaphor for this is to imagine that your brain is a camera and your eyes are the lenses/sensors that take in a picture. Your lens can take in the light and transmits that information into the camera so you can see that breathtaking picture of the Rocky Mountains. The lens glass opens and closes to focus on what’s in front but if the glass is broken/dirty, then your picture is going to look out of touch.

How or Why Do The Following Drugs Cause The Pupils to Dilate?

The medical term for pupil dilation is mydriasis. Miosis is best described as the opposite, which is the pupils constrict. Miosis can be present in the use of other drugs.

The average pupil size sits in a range of 2.0 to 4.0 millimeters. The pupil has sphincter muscles that allow it to open and close in reaction to light. These muscles are also known as the iris or color of the eyes. Such processes allow our eyes to focus on what’s in front of us for protection.

Light sensitivity is a common side effect of drugs that cause pupil dilation. A way of protecting the eyes is to wear sun-protected lenses.

People who have been struggling with substance abuse for extended periods of time often experience long-term health problems. Unfortunately, vision problems aren’t foreign to the repeated damage done to the body due to substance abuse.

For example, persistent dry eyes or degeneration can be worsened by the use of heavy alcohol or tobacco. Also, liver damage from substance abuse can cause jaundice — with the side effect of “yellow eyes.”

Find Help at Discovery Institute

Addiction can be a dark storm of challenges that surround the possibility of true growth. If you or a loved one are grappling with addiction, Discovery Institute is more than happy to offer support. Our mission is to direct you or your loved ones to a program that will fit your needs during these difficult times. Take the first step into the healing process for yourself and those who seek the same peace. Contact us today.

Reviewed for Medical & Clinical Accuracy by The Discovery Institute