Over-the-counter drugs are a form of self medication. The buyer diagnoses his/her own illness and buys a specific drug to treat it. The World Self-Medication Industry (WSMI) define self-medication as the treatment of common health problems with medicines especially designed and labeled for use without medical supervision and approved as safe and effective for such use.
A person may also self-medicate by taking more or less than the recommended dose of a drug.
Some mental illness sufferers attempt to correct their illnesses by use of certain drugs. Depression, for example, is notorious for being a trigger of alcohol, tobacco, cannabis, or other mind-altering drug use. While this may provide immediate relief of some symptoms such as anxiety, it may evoke and/or exacerbate some symptoms of several kinds of mental illnesses that are already latently present, and may lead to addiction/dependence, among other side effects of long-term use of the drug. The theory that drug dependence or addiction results from self-medication for the distress caused by a pre-existing condition was introduced in 1974 by David F. Duncan and Edward J. Khantzian in independent publications. This theory has come to be known as the self-medication hypothesis. For example, sufferers of post-traumatic stress disorder are prone to self-medication, as well as many individual without this diagnosis which have suffered from (mental) trauma.
The current phenomenon in many Western societies of the widespread usage of vitamins, herbs, and other over-the-counter "supplements"--usually without the advice, supervision, or even knowledge of any licensed health professional--is another possible example of self-medication. Some observers of health behavior and medical affairs have speculated that this trend may arise from the desire of laymen to feel more in control of their own health--rather than relying on the traditional medical establishment, whose motives are sometimes seen as suspect. The extraordinary increases in the cost of traditional health care in recent decades--doctors, hospitals, prescriptions, etc.-- causes some individuals to desperately try to find more affordable alternatives to treat or prevent their own afflictions.