Some signs to look out for:

  • Spends less time with friends and family, or has a recent change in friends
  • Seems moodier
  • Skips classes or his grades are slipping
  • Loses interest in hobbies/sports
  • Has red or glassy eyes, at times
  • Smells like marijuana (skunky)
  • Owns pipes, bongs, rolling papers, etc.
  • Suffers regular injuries

Source