Because the effects are felt almost immediately by the smoker, further inhalation can be stopped at any time and the effect therefore regulated. In contrast, those ingesting marijuana experience effects that are slower to develop, cumulative, longer lasting, and more variable, making unpleasant reactions more likely with this method of administration. Popular use of marijuana has arisen from its effects of euphoria, sense of relaxation, increased visual, auditory, and taste perceptions that may occur with low to moderate doses of the drug. Unpleasant effects that may occur include depersonalization, changed body image, disorientation and acute panic reactions or severe paranoia . Some cases of severe delirium and hallucinations have also been reported.
Visual tracking is impaired and the sense of time is typically prolonged.
Learning may be greatly affected because the drug diminishes one's ability to concentrate attention. Regular users, upon discontinuation of marijuana, may experience withdrawal effects. These may include agitation , insomnia , irritability, and anxiety . During the 1980s it was established as the most commonly used hallucinogen, with the majority of users 5 to 25 years old. Although phencyclidine was initially developed by a pharmaceutical company searching for a new anesthetic, it was not suitable for human use because of its psychotropic side effects.