There are many different drugs that people take to alter their mood; many of them are illegal, and all of them cause harm to the body. Most result in dependence, which is an intense need for the drug and an inability to function without it. This need can be physiological, where changes in the body's metabolism make the body need more of the drug, also referred to as physical addiction. The need can also be a psychological addiction, where there is a strong desire to use the drug. Most drugs also cause tolerance, where continued use of the drug causes the body to require larger and larger doses to achieve the same effects. There are four types of drugs, based on how each type affects the user: Depressants: drugs that reduce activity in the central nervous system Alcohol Barbiturates Stimulants: drugs that produce feelings of energy and activation Amphetamines Methamphetamine Caffeine Nicotine Cocaine and Crack Cocaine Opiates: drugs that slow bodily functions Opium, Morphine & Heroin Hallucinogens: drugs that alter sensory perception Magic Mushrooms LSD Cannabis Ecstacy PCP See also a comparison of some drugs and their effects, including addictive potentials. [NOTE: The facts contained in these pages are for informational use only. If you are seeking complete and accurate information about drugs and their effects, you should consult a health care professional.] Resources