Why are some drugs addictive?
Scientists think that all addictive drugs activate the brain's 'reward system', by increasing the release of the chemical dopamine from neurons in key areas of the brain. Dopamine release occurs after pleasurable experiences, for example after food or sex, but can also be induced by some drugs. Drugs that artificially increase dopamine release in this way may cause craving for more. It is possible that some people may have a genetic tendency to make them develop drug addictions extremely rapidly.