The Science Behind "High Eyes"
At the core of how drugs affect eye appearance lies the central nervous system (CNS), which controls the involuntary muscles that regulate pupil size. The autonomic nervous system, a division of the CNS, has two branches that often have opposing effects: the sympathetic and parasympathetic systems.
- Sympathetic Nervous System: This system is responsible for the "fight or flight" response. When activated, it releases neurotransmitters like norepinephrine, which trigger the iris's dilator muscles to widen the pupils (mydriasis).
- Parasympathetic Nervous System: This system controls the body's "rest and digest" functions. Its activation causes the iris's sphincter muscles to contract, constricting the pupils (miosis).
Various medications and illicit substances interfere with this delicate balance, leading to the characteristic visual signs of being "high.".
Effects of Different Drug Classes
Different types of drugs, based on their pharmacological action, produce distinct and often opposite effects on the eyes.
How Stimulants Affect the Eyes
Stimulants like cocaine, methamphetamine (meth), and ecstasy (MDMA) increase the levels of neurotransmitters such as dopamine and norepinephrine in the brain. This triggers a prolonged sympathetic nervous system response, leading to noticeably dilated pupils.
- Cocaine: Users may exhibit dilated pupils, which can occur within minutes of use and last for hours, alongside redness and light sensitivity.
- Methamphetamine: Methamphetamine can cause mydriasis that lasts for 3 to 8 hours and can be accompanied by rapid eye movements (nystagmus) and a jittery gaze.
- Hallucinogens (LSD, Psilocybin): Psychedelic drugs, which increase serotonin levels, also cause significant pupil dilation. This is often associated with the visual hallucinations experienced during a trip.
How Depressants Affect the Eyes
Depressants slow down the CNS. This class includes opioids and alcohol, which both trigger the parasympathetic nervous system but have different visual effects.
- Opioids (Heroin, Fentanyl, Oxycodone): These drugs cause extreme pupil constriction, resulting in pupils that appear like tiny pinpoints (miosis). This effect is a classic sign of opioid use and is often unresponsive to changes in light. Droopy eyelids and a drowsy appearance are also common.
- Alcohol: Heavy alcohol consumption causes blood vessels in the eyes to dilate, leading to redness. As a diuretic, alcohol also causes dehydration, which can result in dry, glassy eyes and blurred or double vision.
How Cannabis Affects the Eyes
Marijuana's psychoactive compound, THC, causes a temporary lowering of blood pressure. This allows blood vessels in the eyes (ocular capillaries) to dilate, which is the primary cause of red, bloodshot eyes. This effect can occur whether the cannabis is smoked or consumed as an edible, debunking the myth that redness is solely from smoke irritation. While red eyes are most common, some users may also experience mild pupil dilation.
Long-Term Eye Health Complications
Chronic or long-term substance abuse can lead to more serious and potentially irreversible damage to eye health.
- Retinopathy: Conditions like talc retinopathy can develop from injecting drugs containing talc fillers, which can cause blockages in the retinal blood vessels.
- Glaucoma: Long-term cocaine or meth use can damage retinal blood vessels, increasing the risk of conditions like glaucoma.
- Keratitis: Stimulants like methamphetamine can reduce the blinking reflex, leading to dry eyes and potential inflammation or damage to the cornea.
- Optic Neuropathy: Chronic alcohol or drug abuse can be toxic to the optic nerve, causing damage that can result in vision loss.
Can You Identify What Drug Someone Used from Their Eyes?
While eye appearance provides clues about a person's state, it is not a definitive diagnostic tool. Many non-drug-related factors can cause similar symptoms:
- Dilated Pupils: Can also be a response to low light, emotional excitement, or certain prescribed medications like antidepressants.
- Pinpoint Pupils: Can occur with some medical conditions or as a side effect of certain medications.
- Red Eyes: Can be caused by allergies, fatigue, eye strain, or infection.
Comparative Eye Effects by Substance Class
| Substance Class | Pupil Size Effect | Eye Color & Appearance | Common Eye Movement | Pharmacological Cause |
|---|---|---|---|---|
| Stimulants | Dilated (Mydriasis) | Redness, intense gaze | Nystagmus (rapid, involuntary movements) | Increased norepinephrine and dopamine |
| Depressants (Opioids) | Constricted (Miosis), pinpoint | Droopy, drowsy appearance | Reduced, slow movement | Activation of parasympathetic nervous system |
| Depressants (Alcohol) | Dilated (with intoxication) | Red, bloodshot, glassy | Nystagmus, poor coordination | Vessel dilation, dehydration, CNS effects |
| Hallucinogens | Dilated (Mydriasis) | May be red or watery | Altered processing, visual effects | Increased serotonin and altered brain activity |
| Cannabis | Redness is most common; mild dilation possible | Bloodshot, red, watery | Slower focus, altered processing | THC-induced blood pressure drop and vessel dilation |
Conclusion
Observable eye changes when high are a direct consequence of a substance's pharmacological effects on the central nervous system. Different drug classes have distinct impacts, from the pronounced pupil constriction caused by opioids to the bloodshot redness typical of marijuana use. However, these visible signs should never be used as a definitive diagnosis of substance use, as many non-drug-related factors can cause similar symptoms. Long-term or heavy substance abuse can also lead to severe and permanent eye damage, including various forms of retinopathy and optic nerve toxicity, highlighting the serious health risks involved. If you or someone you know is struggling with substance use, seeking professional help is crucial for both eye health and overall well-being. American Addiction Centers provides information on how various substances affect eye health, and can be a valuable resource for further information.
