Recreational drug use is the use of one or more psychoactive drugs to induce an altered state of consciousness either for pleasure or for some other casual purpose or pastime. When a psychoactive drug enters the user's body, it induces an intoxicating effect. Generally, recreational drugs are divided into three categories: depressants (drugs that induce a feeling of relaxation and calmness), stimulants (drugs that induce a sense of energy and alertness), and hallucinogens (drugs that induce perceptual distortions such as hallucination). In popular practice, recreational drug use generally is a tolerated social behaviour, rather than perceived as the medical condition of self-medication. However, heavy use of some drugs is socially stigmatized. Many people also use prescribed and controlled depressants such as opioids, as well as opiates and benzodiazepines. Common recreational drugs include caffeine, commonly found in coffee, tea, soft drinks, chocolate; alcohol, commonly found in beer, wine, and distilled spirits; nicotine, commonly found in tobacco and electronic cigarettes; cannabis and hashish (with legality of possession varying inter/intra-nationally); and the controlled substances listed as controlled drugs in the Single Convention on Narcotic Drugs (1961) and the Convention on Psychotropic Substances (1971) of the United Nations. What controlled substances are considered generally unlawful to possess varies by country, but usually includes cannabis, cocaine, opioids, MDMA, amphetamine, methamphetamine, psychedelics, benzodiazepines, and barbiturates. it is estimated that about 5% of people worldwide aged 15 to 65 (158 million to 351 million) had used controlled drugs at least once. Reasons for use Many researchers have explored the etiology of recreational drug use. Some of the most common theories are: genetics, personality type, psychological problems, self-medication, sex, age, depression, curiosity, boredom, rebelliousness, a sense of belonging to a group, family and attachment issues, history of trauma, failure at school or work, socioeconomic stressors, peer pressure, juvenile delinquency, availability, historical factors, or socio-cultural influences. There has been no consensus on a single cause. Instead, experts tend to apply the biopsychosocial model. Any number of factors may influence an individual's drug use as they are not mutually exclusive. Regardless of genetics, mental health, or traumatic experiences, social factors play a large role in exposure to and availability of certain types of drugs and patterns of use. According to addiction researcher Martin A. Plant, some people go through a period of self-redefinition before initiating recreational drug use. They tend to view using drugs as part of a general lifestyle