Hallucinogens change one's behaviour, thoughts, feelings and perceptions without any actual sensory stimulus.
Sedative: Barbiturate and benzodiazepines -Depress brain activity and produce feelings of calmness, relaxation, drowsiness and deep sleep.
Stimulant: Caffeine, cocaine, amphetamines-Stimulate nervous system, increases alertness, produce excitement.
Tranquilisers: Benzodiazepines-Act as anti-depressants.