A client exhibiting symptoms of anxiety and social withdrawal might have ingested which psychoactive substance?

The correct answer is cannabis, as it can lead to symptoms of anxiety and social withdrawal in some individuals. While cannabis is often associated with relaxation and social enjoyment, it can also exacerbate feelings of anxiety, particularly in users who may be predisposed to anxiety disorders. Moreover, regular or excessive use can result in withdrawal from social situations, as some users may seek to avoid cannabis-related anxiety or paranoia by isolating themselves.

On the other hand, substances like cocaine and alcohol typically produce different effects; cocaine is a stimulant that can lead to increased energy and sociability, while alcohol is a depressant that can initially reduce social inhibitions but may subsequently lead to aggressive or depressive behaviors rather than withdrawal. Heroin, while it may contribute to social withdrawal, is more commonly associated with sedation and decreased motivation but does not typically present with anxiety as a primary symptom. Thus, cannabis is the substance most aligned with both anxiety and social withdrawal.