Drugs are chemical substances. There are three different types of drugs: stimulants, depressants and hallucinogens.
Stimulants speed up the central nervous system. They increase heart rate, blood pressure and breathing. Examples are caffeine, nicotine, amphetamines, ecstasy and cocaine.
Depressants slow down the central nervous system. They decrease heart and breathing rates. Alcohol, heroin and analgesics are common examples of these types of drugs.
Hallucinogens change mood, thought and senses. LSD is the most well-known example of this type of drug.