Unusually large pupils can be a noticeable sign. While pupil size naturally changes with light, persistent dilation, where the dark center of the eye remains wider than normal, can be linked to various substances. This phenomenon is frequently associated with certain drugs.
Understanding Pupil Dilation
The medical term for dilated pupils is mydriasis. This condition describes pupils widening without a change in light levels. The pupil’s function is to regulate the amount of light entering the eye. Muscles within the iris, the colored part of the eye, control pupil size.
Pupil size is managed by the autonomic nervous system, which has two main branches: the sympathetic and parasympathetic nervous systems. The sympathetic nervous system, associated with the “fight or flight” response, causes pupils to dilate. Conversely, the parasympathetic nervous system promotes constriction, making pupils smaller. Certain substances can interfere with this balance, leading to noticeable pupil dilation.
Substances Leading to Dilated Pupils
Many drugs can cause pupils to dilate by influencing the autonomic nervous system’s control over pupil size. This effect depends on the substance and its interaction with the body’s neurochemistry.
Stimulants
Stimulants are a common category of drugs that cause pupil dilation. These substances, including cocaine, amphetamines like Adderall and crystal meth, and MDMA (ecstasy), activate the sympathetic nervous system. This activation leads to an increased release of neurotransmitters such as norepinephrine, which stimulates the dilator muscle in the iris, causing the pupils to widen.
Hallucinogens
Hallucinogens frequently cause dilated pupils due to their impact on neurotransmitter systems in the brain. Substances like LSD, psilocybin (found in magic mushrooms), and mescaline primarily affect serotonin receptors. Psilocybin, for example, triggers serotonin release, which overstimulates the nervous system and results in enlarged pupils, enhancing visual sensitivity.
Anticholinergic Substances
Anticholinergic substances block the action of acetylcholine, a neurotransmitter that normally causes pupils to constrict. By inhibiting this system, anticholinergics lead to unopposed sympathetic activity, resulting in pupil dilation. Examples include atropine, scopolamine, certain antihistamines like diphenhydramine when taken in high doses, and some tricyclic antidepressants.
Opioid Withdrawal
Opioid withdrawal presents a contrast to opioid use, which typically causes constricted, or “pinpoint,” pupils. During withdrawal from opioids, the body reacts to the absence of the drug by activating the sympathetic nervous system, leading to dilated pupils.
Other Causes
Other causes of dilated pupils include specific eye drops used by ophthalmologists during eye examinations. These “mydriatic” eye drops directly stimulate the iris muscles to dilate the pupils, allowing for a better view of the retina.
When to Seek Help
While some instances of dilated pupils are temporary or medically induced, persistent or sudden dilation warrants attention. Dilated pupils, especially when suspected to be drug-related, can sometimes indicate a dangerous reaction or an overdose.
Seek immediate medical attention if dilated pupils are accompanied by other concerning symptoms. These include altered mental status, difficulty breathing, seizures, a rapid heart rate, severe agitation, or if the person becomes unresponsive. If pupils remain dilated for a long period, do not react normally to light, or if one pupil is larger than the other, a medical evaluation is advisable to rule out underlying conditions, even if drug use is not suspected.