Cerebellar hypoactivity in frequent marijuana users

It is uncertain whether frequent marijuana use adversely affects human brai n function. Using PET, regional cerebral blood flow was compared in frequen t marijuana users and comparable, non-using controls after at least 26 h of monitored abstention by all subjects. Marijuana users showed substantially lower brain blood flow than controls in a large region of posterior cerebe llum, indicating altered brain function in frequent marijuana users. A cere bellar locus of some chronic and acute effects of marijuana is plausible, e .g. the cerebellum has been linked to an internal timing system, and altera tions of time sense are common following marijuana smoking. NeuroReport 11: 749-753 (C) 2000 Lippincott Williams & Wilkins.