Content medically reviewed by Vicky Magobet, PMHNP-BC, on June 24, 2021.
When an individual does drugs, others can often tell because they display several noticeable signs. These signs can be physical, behavioral or psychological.
One of the most common signs that a person may be abusing drugs is having dilated pupils. The dilation level of a person's pupils is one of the main ways of recognizing illicit drug use. Along with alerting others that an individual may be struggling with substance abuse, dilated pupils can also help reveal what specific drug they are using.
Your pupils, or the small black dots in the center of your eye, change sizes based on the amount of light entering your eyes. By regulating the light, your pupils help you focus and maintain better vision in a range of lighting conditions.
While factors such as your iris — the colored part of your eye — and emotions can influence the size of your pupils, chemical changes can cause much more discernible shifts in size.
Chemical changes can include medications as well as illicit drugs. When these kinds of drugs are taken, they can affect either the parasympathetic or sympathetic nervous system. Sometimes, just one system is affected — at other times, both are. When this happens, the drug will affect the brain's neurotransmitters, which then cause the pupils to dilate.
Several different types of drugs — both legal and illegal — can dilate pupils and indicate to friends, family members and authorities that an individual may be under the influence or abusing a specific substance. The International Association of Chiefs of Police (IACP) has even created standards to determine which type of substance an individual could be using based on their pupil diameter.
While various drugs, especially psychotropic stimulants, can cause the pupils to dilate, 10 of the most common drugs that can trigger this include:
Keep in mind though that some of these drugs will affect more than just the pupils, making it important to be aware of the other signs of illicit drug usage. Some common indicators of drug usage include:
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