What is a common effect of CNS depressants on pupil size?

CNS depressants, such as alcohol, benzodiazepines, and opioids, commonly induce a state of relaxation and sedation within the central nervous system. One of the physiological responses to these substances is the constriction of pupils, a condition known as miosis. This is due to the effect of depressants on the autonomic nervous system, specifically through the stimulation of the parasympathetic nervous system, which leads to the contraction of the iris sphincter muscle, resulting in smaller pupil size.

This is in contrast to other categories of substances, such as stimulants which typically cause pupil dilation (mydriasis). When assessing a person suspected of drug influence, recognizing the characteristic pupil size associated with CNS depressant use can be an important indicator in a drug recognition evaluation.