Adolescence is a natural period of experimentation.
If you notice any of these symptoms, don't preach, lecture, or lash out. Instead, discuss the substance use calmly and frankly. Marijuana is the most commonly used illicit drug around. It's a mild hallucinogen that may also produce euphoria, apathy, poor coordination, reddened eyes, increased appetite, increased heart rate, panic attacks, and short-term memory loss. Doesn't sound like too much fun.