Drugs can cause noticeable changes in the size of our pupils, offering a window into the state of someone’s intoxication or drug use. The pupils, the dark circles in the middle of our eyes, respond to various substances, sometimes becoming larger or smaller depending on what’s in the system. These changes aren’t just random; they provide clues about how the body is reacting to a drug.
Why Do Pupils Dilate on Drugs?
Pupils can become noticeably larger or smaller depending on the drug someone has used. The reason this happens has to do with how the body responds to different substances. Our eyes have muscles that control the size of our pupils, and these muscles are controlled by the autonomic nervous system. This system reacts to things like light, emotional states, and drugs.
Some drugs trigger the sympathetic nervous system, which prepares the body for action. This system is responsible for what’s called the “fight or flight” response, and it often causes pupils to dilate, or widen. When pupils dilate, it allows more light into the eyes, which can improve vision in low-light conditions.
Drugs that stimulate this system—like methamphetamine, cocaine, and ecstasy—can cause pupils to dilate to a noticeable extent. This is a natural, physiological response that helps the body become more alert. The bigger pupils let more light in, which is why people often feel more aware when using these drugs.
On the other hand, some drugs have the opposite effect, causing the pupils to constrict or shrink. This is often seen with opioids and benzodiazepines. These depressant drugs slow down the central nervous system, and as a result, the muscles in the eye tighten, making the pupils smaller.
What Do Pupils Look Like When on Drugs?
When someone is under the influence of certain drugs, their pupils can look noticeably different. Drugs can cause either dilated or constricted pupils, which can be a quick giveaway that a person has used something.
- Dilated Pupils: With stimulants like methamphetamine, cocaine, and ecstasy, the pupils often become very large. The iris, the colored part of the eye, becomes so expanded that the white part (the sclera) becomes much more visible. The pupils can look almost black in the light, especially if the person is in a bright setting. People using hallucinogens like LSD or mushrooms may also have dilated pupils. The enlargement is due to the stimulation of the sympathetic nervous system, which puts the body on high alert and opens the pupils wide. The effect can be quite dramatic, with some users having pupils so large that it makes them appear almost unreal or unnatural.
- Pinpoint Pupils: On the other side, drugs like opioids cause the pupils to shrink to tiny, pinpoint size. This is a classic symptom of opioid use or overdose. The pupils become so small that they almost disappear, making it difficult to see much of the iris at all. This is a result of the drug’s sedative effects, which slow down the central nervous system and tighten the muscles controlling pupil size.
- Variable Pupils: Some substances, like LSD or psilocybin mushrooms, can cause pupils to fluctuate between dilation and constriction, depending on the dose or the individual’s sensitivity. This shifting pupil size adds to the altered sensory experiences often caused by hallucinogens. A person on these drugs might experience moments of intense pupil dilation followed by moments of constriction.
- Bloodshot Eyes: Some drugs, especially marijuana, cause the eyes to become red or bloodshot. This is due to the dilation of blood vessels in the eyes, but it doesn’t necessarily correlate with the pupil size. When someone smokes or consumes cannabis, it’s not unusual for their eyes to look red, and the pupils may become slightly larger than usual.
By watching for these changes in pupil size, it’s possible to tell whether someone might be under the influence of a drug.
How Stimulant Drugs Affect the Pupils
Stimulants like methamphetamine, cocaine, and ecstasy can cause dramatic changes to the eyes, most notably pupil dilation. These drugs trigger the sympathetic nervous system, which is responsible for the body’s “fight or flight” response. This system gets activated when the body needs to become alert or prepared for action, and one of the ways it does this is by dilating the pupils.
When someone takes a stimulant, the increased norepinephrine in the brain results in larger, more open pupils. This effect can be so extreme that, in some cases, the pupils may become almost unrecognizable. The dilation happens because the nervous system is preparing the body to handle more intense stimuli, heightening awareness and making it easier to see in darker settings.
For example, cocaine causes a noticeable enlargement of the pupils, even in well-lit conditions. Similarly, with methamphetamine use, the pupils can become so dilated that they remain in a permanently wide state during the high. While the user may feel more awake and alert, the impact on the eyes is one of the easiest physical cues that someone has used a stimulant.
The effect is also seen with ecstasy (MDMA), where pupils can dilate significantly as the drug raises serotonin levels in the brain. The increase in serotonin makes users feel more euphoric, and as a side effect, the eyes widen as part of the body’s heightened state of awareness. In addition to dilating pupils, stimulants like these often cause users to be hyperactive and restless.
How Depressant Drugs Affect the Pupils
Depressant drugs, such as opioids and benzodiazepines, have the opposite effect on the pupils compared to stimulants. These drugs slow down the activity of the central nervous system, which results in smaller pupils. The pupils constrict, becoming pinpoint or nearly invisible in some cases.
Opioids like heroin, morphine, or prescription painkillers, as well as benzodiazepines like Xanax or Valium, cause a sedative effect on the body. This sedative action reduces the body’s alertness and decreases the sympathetic nervous system activity, which in turn leads to pupil constriction.
The constriction of the pupils is one of the clearest signs of opioid use, particularly in overdose situations. This is often called “pinpoint pupils,” a telltale sign that doctors and emergency responders look for when treating opioid overdoses.
How Hallucinogenic Drugs Affect the Pupils
Hallucinogenic drugs, such as LSD and psilocybin mushrooms (commonly known as magic mushrooms), have a unique effect on the eyes. These substances can cause both pupil dilation and constriction, depending on various factors such as dosage and individual sensitivity.
When someone takes a hallucinogen, the initial effect is usually pupil dilation. This happens because these drugs stimulate the serotonin receptors in the brain, which plays a major role in mood regulation, perception, and sensory experiences. As a result, the sympathetic nervous system is activated, and the pupils dilate, allowing more light into the eyes and enhancing visual sensations. The dilation is often very noticeable, and it’s one of the key signs of hallucinogenic drug use.
However, as the effects of hallucinogens intensify, the pupils may begin to constrict. This fluctuation in pupil size adds to the strange, unpredictable sensory experience that many users report while on drugs like LSD or mushrooms. The pupils may rapidly switch between dilating and contracting, which can further distort the perception of reality. It’s not uncommon for a person on hallucinogens to have large, unblinking pupils for a period, followed by sudden constriction.
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Marijuana’s Effect on the Pupils
Marijuana, or cannabis, affects the pupils in a way that is similar to other drugs that dilate the pupils, though the effect is typically less extreme. When someone uses marijuana, the primary psychoactive compound, THC (tetrahydrocannabinol), interacts with receptors in the brain and alters perception, mood, and cognitive function. One of the physical side effects of cannabis use is pupil dilation, which can be noticeable but not as dramatic as with stronger stimulants.
People who have consumed marijuana often have larger pupils, even if they are in a well-lit environment. This is due to the activation of the sympathetic nervous system, which responds to THC by triggering the dilation of the pupils. This effect can last for a few hours after smoking or ingesting cannabis, depending on the potency and the person’s tolerance.
In addition to pupil dilation, marijuana use often causes bloodshot eyes, another common indicator of use. While the dilation can last for several hours, the effects typically wear off as the high diminishes.
Alcohol’s Effect on the Pupils
Alcohol is another substance that has variable effects on pupil size. The effects depend on the amount consumed and the individual’s tolerance. Initially, alcohol may cause pupil constriction due to its depressant effects on the nervous system. This is typical of drugs that slow down brain activity, such as opioids and benzodiazepines.
However, with higher alcohol consumption or extreme intoxication, the body’s natural response may shift, and the pupils could dilate instead. This change happens as the body tries to compensate for the sedative effects of alcohol. The dilation can be more noticeable in individuals who have consumed large amounts of alcohol, and it can be accompanied by other symptoms of drunkenness, such as difficulty balancing or impaired speech.
Alcohol-induced pupil dilation is often a sign of severe intoxication and can be a clue that someone has consumed an excessive amount. The eyes may also appear glassy or unfocused, which is another indicator of alcohol use. As with other substances, the extent of pupil changes can vary based on factors such as individual tolerance, the amount consumed, and the presence of other substances in the body.
Prescription and Over-the-Counter Drugs’ Effects on the Pupils
Certain prescription medications and over-the-counter drugs can also influence pupil size, either causing dilation or constriction. Opioid pain relievers, such as oxycodone, hydrocodone, and fentanyl, are among the most common drugs that cause pupils to constrict. These medications are often prescribed to manage pain, but they come with the side effect of constricting pupils, which is a hallmark of opioid use.
In addition to opioids, other prescription drugs can cause changes in pupil size. For example, certain antidepressants, like selective serotonin reuptake inhibitors (SSRIs), and antihistamines can cause pupil dilation. This is because these drugs affect neurotransmitter systems in the brain, influencing both mood and perception. The effect on pupils may not be as noticeable as with stimulants or opioids, but it is still worth noting.
Similarly, some over-the-counter drugs, such as antihistamines and decongestants, can dilate the pupils. These medications often work by blocking certain receptors in the body, which can lead to temporary pupil dilation. The degree of dilation varies depending on the individual and the medication.
Long-Term Effects of Substance Misuse on Eye Health
Substance misuse can have both immediate and lasting effects on eye health, with some issues being temporary and others leading to permanent damage. While short-term symptoms like double vision, changes in pupil size, eyelid twitching, and trouble seeing in low light often disappear once the substance leaves the body, long-term misuse can result in more serious and enduring eye conditions.
For example, retinal ischemia, which occurs when the retina doesn’t receive enough blood supply, can cause lasting damage to vision. Optic neuropathy, where the optic nerve is damaged and can’t properly transmit visual information to the brain, may also develop from chronic substance misuse.
Some vision-related conditions may not show up right away but develop gradually with continued substance use. Here are a few eye issues that can worsen over time:
- Age-Related Macular Degeneration (ARMD): This condition causes loss of central vision and is common in those over 50. However, chronic alcohol and tobacco misuse may accelerate the development of ARMD.
- Dry Eyes: Regular alcohol consumption can lead to chronic dry eyes, a condition where the eyes don’t produce enough tears, causing irritation and discomfort. This issue is separate from alcohol intoxication itself but can persist over time.
- Keratitis: This inflammation of the cornea can distort vision. Drugs like cocaine, especially when used topically, can contribute to the onset of keratitis, and untreated cases may lead to severe complications like corneal ulcers.
- Endophthalmitis: This severe eye infection can occur when bacteria enter the bloodstream, often from sharing needles, and spread to the eyes, causing inflammation and potential vision loss.
- Glaucoma: Substance misuse that alters blood pressure can affect fluid pressure inside the eye, potentially leading to glaucoma. Some studies suggest a connection between alcohol use and substance-induced glaucoma, though the relationship remains unclear.
- Nystagmus: The rapid, involuntary movement of the eyes is often associated with intoxication from a variety of substances.
- Retinal Vascular Occlusive Disease (RVOD): This condition occurs when blood clots or changes in blood pressure block healthy blood flow to the retina. Over time, this can cause vision loss. RVOD can be linked to substance misuse, particularly in individuals with high blood pressure or diabetes, which can develop as a result of addiction.
- Talc Retinopathy: Associated with intravenous drug use, this condition involves the buildup of talc in the eye’s blood vessels, leading to retinal damage, vision impairment, and, potentially, retinal ischemia.
Notice Someone’s Pupils on Drugs? Get Help for Drug and Alcohol Misuse or Addiction
Pupil size can be a noticeable sign of drug use, with stimulants and hallucinogens typically causing dilation, while depressants like opioids and benzodiazepines often lead to constriction. Alcohol can cause both responses depending on how much is consumed, and certain prescription drugs can either dilate or constrict the pupils.
However, while pupil changes can offer clues about possible drug use, they’re not a foolproof indicator on their own. Other factors, such as lighting or emotional reactions, can also influence pupil size. Knowing how different substances affect the eyes helps provide insight into their effects on the body, but it’s just one part of the bigger picture when it comes to recognizing potential drug use.
If you or someone you care about struggles with substance misuse or addiction, Woburn Addiction Treatment is ready to support you. Our team of treatment professionals, including physicians, counselors, and healthcare providers, can guide you through the recovery process and offer the support you need to overcome addiction.
Call (781) 622-9190 today. Our compassionate admissions team is here 24/7 to listen, answer your questions, and help you find the best path to recovery.
