Considering that the experimental behaviors studied are likely correlates of more complex, integrated, daily behavior, marijuana use should be viewed as potentially disruptive to education, work performance, and various behaviors involving complex psychomotor control. Available evidence also clearly demonstrates that the amount of tetrahydrocannabinol (THC) is an important determinant of the magnitude of marijuana effects. It is often difficult, however, to determine what the actual dose is in many experimental studies and to subsequently extrapolate this dose to real life usage. For instance, although the concentration of THC and the weight of marijuana cigarettes smoked is usually provided in studies of smoked marijuana, the actual amount of THC delivered can vary due to differences in smoking topography. Practical issues involving the association of marijuana use with behavioral impairments are apparent from the experimental studies. In particular, biological sample testing indicates that the window of time in which marijuana produces acute behavioral impairments is similar to the window of time in which THC is in the bloodstream. Although the experimental studies identify many effects of marijuana, it is difficult to predict how and to what degree these effects disrupt daily functioning, especially in inexperienced users. Rapid advancements have occurred in the understanding of the neurobiological basis of marijuana effects, but the current understanding of the implications of cannabinoid receptors and the naturally occurring ligands for human behavior is still limited. 73 references