How does pupil size typically change in response to stimulant drugs?

Pupil size typically increases in response to stimulant drugs, a phenomenon known as mydriasis. Stimulants such as amphetamines, cocaine, and methamphetamine activate the sympathetic nervous system, which can lead to various physiological responses, including dilation of the pupils. This effect occurs because stimulants increase the levels of certain neurotransmitters, such as norepinephrine, that trigger the dilation of the iris sphincter muscle.

In a drug recognition context, recognizing this response is crucial for identifying impairment caused by stimulant use. Mydriasis is a clear indicator that can aid law enforcement and medical professionals in assessing an individual's drug influence during evaluations.