Drugs can be broadly divided into three categories based on their main effects.
They may act solely as stimulants, depressants or hallucinogens. Quite a few drugs show two of these effects at the same time, and are then described either as stimulant hallucinogens (e.g. ecstasy) or as depressant hallucinogens (e.g. cannabis).
Stimulants make you feel like you have lots of energy and confidence. They include cocaine, speed, ecstasy, and mephedrone.
Depressants make you feel relaxed and chilled out. They include alcohol, tranquillisers, heroin and cannabis.
Hallucinogens can make you view reality in distorted way and sometimes cause vivid hallucinations. They include LSD and magic mushrooms.
In addition to these 3 broad categories, each particular drug has its own specific effects and risks.
When you obtain drugs anywhere other than from a reliable pharmacy, it can be difficult to say exactly what effects and risks the drug may have. A drug may be quite new and its harms may not yet be fully known, or the drug you are actually taking may not be what you believe it to be (e.g. both PMA and mephedrone have been sold as MDMA/ecstasy). Information on the known effects of each drug is available in the A-Z of drugs.