Answer
Stimulants: Increase alertness and energy levels (e.g. caffeine)
Depressants: Slow down the central nervous system and induce relaxation (e.g. alcohol)
Hallucinogens: Alter perception, thoughts, and feelings (e.g. LSD)
Opioids: Reduce pain and induce euphoria (e.g. morphine)
Anabolic steroids: Increase muscle mass and strength.