What is a common symptom of drug abuse in students?

A common symptom of drug abuse in students is dry mouth. This occurs due to the way many substances affect the body's physiological functions. Drugs can impair salivary gland function, leading to decreased saliva production and resulting in the sensation of a dry mouth. Additionally, dry mouth can be a side effect of various illicit drugs as well as prescription medications when misused.

The other options suggest positive or neutral behaviors that are not typically associated with drug abuse. Optimized physical appearance, increased academic interest, and regular exercise habits indicate healthy lifestyle choices and engagement, which are often compromised when a student is struggling with substance use. Therefore, dry mouth stands out as a clear, relevant indicator of potential drug abuse among students.