The degree of impairment depends on the dose and potency of the drug, the individual's tolerance, and the complexity of the task. Many feelings experienced by marijuana users are subjective in nature. Feelings may include euphoria, relaxation and hilarity, and negative psychological reactions include panic attacks, anxiety and hallucinations. Although it is difficult to measure objectively, researchers have expressed concern over marijuana's effects on motivation. A picture has emerged of amotivational syndrome , which can be described as a massive and persistent loss of ambition that is replaced by chronic apathy and passivity toward goals and the future.
Amotivational syndrome is seen most frequently in heavy marijuana users.
Tolerance to a drug develops when increasing doses of a drug are required to produce the same effect. If marijuana use is infrequent or doses are small, tolerance to the drug is not apparent. After prolonged use, however, it is necessary to ingest more marijuana to produce the same feelings. The fact that the body stores THC may be a factor in developing tolerance. Physical dependence is manifested when an interruption of drug use produces physical withdrawal symptoms.