The pupil, the dark opening at the center of the eye, regulates the amount of light reaching the retina. The iris, the colored part of the eye, controls the pupil’s size, allowing the eye to adapt to varying light conditions.
How Methamphetamine Affects Pupil Size
Methamphetamine typically causes pupils to dilate, a condition known as mydriasis. This is a common physical indicator of methamphetamine use. Individuals under the influence may exhibit noticeably larger pupils, contributing to a “wide-eyed” or “glassy” appearance. This dilation can persist for several hours after the drug is consumed.
The Science Behind Pupil Dilation
The size of the pupil is controlled by two opposing branches of the autonomic nervous system: the sympathetic and parasympathetic systems. Dilation occurs when the sympathetic nervous system is activated. Methamphetamine acts as a powerful stimulant, triggering this “fight or flight” response.
Methamphetamine increases the release of neurotransmitters like norepinephrine and dopamine in the brain. Norepinephrine stimulates the iris’s radial muscles, causing them to contract and pull the pupil open. Dopamine also contributes to this dilating effect.
Pupil Changes Caused by Other Substances
Pupil size changes are not exclusive to methamphetamine and vary significantly depending on the substance. Certain drugs cause pupil constriction, known as miosis, making them appear abnormally small or “pinpoint.” Opioids, including heroin, fentanyl, oxycodone, hydrocodone, morphine, codeine, and methadone, are known for this effect, resulting from parasympathetic nervous system activation. Some antipsychotic medications and eye drops, such as pilocarpine, can also lead to miosis.
Many other substances, particularly stimulants and hallucinogens, also cause pupil dilation. Examples include cocaine, MDMA (ecstasy), amphetamines, LSD, psilocybin, and mescaline. Alcohol, cannabis, ketamine, and bath salts can also lead to dilated pupils. Observing pupil size alone is not a definitive diagnostic tool for substance use, as various factors can influence it.
Additional Physical Signs of Methamphetamine Use
Beyond pupil changes, several other physical signs can indicate methamphetamine use. Individuals may exhibit increased energy, hyperactivity, and restlessness, often accompanied by rapid speech. Significant weight loss and a gaunt appearance are common due to the drug’s appetite-suppressing effects.
Skin issues, such as sores, rashes, or infections, can develop from compulsive skin picking. Severe dental problems, often termed “meth mouth,” characterized by tooth decay and gum disease, are a frequent physical manifestation. Other indicators include rapid eye movements, a twitchy gaze, bloodshot eyes, and disturbed sleep patterns like insomnia.