Sub-chronic (i.e.,< 8 weeks) or chronic (>8 weeks) stimulant responses have been measured in patients receiving methylphenidate for ADHD or bupropion for smoking cessation. Other studies have examined the phenotypes of dependence, abuse, and consequences of abuse such as drug-induced psychosis. Although it is not possible to accurately determine the doses in studies of active drug abusers, it is safe to assume that they involve higher doses than are found in acute or therapeutic studies. In addition, drug users commonly self-administer drugs via injection, inhalation (smoking) or intranasal routes, where the acute laboratory studies and therapeutic studies most commonly involve oral administration.
