Psychoactive drugs may be divided into four categories:
- Depressants: Drugs that decrease alertness by slowing down the activity of the central nervous system (e.g. heroin, alcohol and analgesics).
- Stimulants: Drugs that increase the body's state of arousal by increasing the activity of the brain (e.g. caffeine, nicotine, amphetamines and cocaine).
- Hallucinogens: Drugs that alter perception and can cause hallucinations, such as seeing or hearing something that is not there (e.g. LSD and 'magic mushrooms').
- Other: Some drugs fall into the 'other' category, as they may have properties of more than one of the above categories (e.g. cannabis has depressive, hallucinogenic and some stimulant properties).