Change in effects from marijuana: a five- to six-year follow-up.

A five- to six-year follow-up study of 97 regular marijuana users in a large Midwestern city showed that the effect of marijuana intoxication remained fairly stable over time. However, continued use of the drug was associated with a decrease in pleasurable effects. Undesirable effects persisted but apparently did not discourage continued use. Decreases found in some undesirable effects (tachycardia, lightheadedness, and dry mouth) raised the possibility that some degree of tolerance had developed.