CONTEXT: Hepatotoxicity is a potential complication from the usage of various illicit drugs, possibly consequent to their liver metabolism, but information on this is scarce in the medical literature. OBJECTIVE: To study the occurrence of clinical and laboratory hepatic alterations in chronic marijuana users, from the use of marijuana on its own or in association with other legal or illicit drugs. TYPE OF STUDY: transversal study SETTING: Hospital Espírita de Marília, Marília, São Paulo, Brazil PARTICIPANTS: The study was made among 123 patients interned in the Hospital Espírita de Marília from October 1996 to December 1998, divided into 3 groups: 26 (21%) using only marijuana, 83 (67.5%) using marijuana and crack, and 14 (11.4%) consuming marijuana and alcohol. PROCEDURES AND MAIN MEASUREMENTS: Patients were examined clinically with special emphasis on types of drugs used, drug intake route, age when consumption began, length and pattern of usage, presence of tattooing, jaundice, hepatomegaly and splenomegaly. Serum determinations of total proteins, albumin, globulin, total and fractions of bilirubin, aspartate (AST) and alanine (ALT) aminotransferases, alkaline phosphatase (AP), gamma-glutamyltransferase and prothrombin activity were performed. RESULTS: Among users of only marijuana, hepatomegaly was observed in 57.7% and splenomegaly in 73.1%, and slightly elevated AST (42.3%), ALT (34.6%) and AP (53.8%). The three groups did not differ significantly in the prevalence of hepatomegaly, splenomegaly and hepatosplenomegaly. The group using both marijuana and alcohol showed the highest prevalence of alterations and highest levels of aminotransferases. Mean AP levels were above normal in all groups. CONCLUSIONS: Chronic marijuana usage, on its own or in association with other drugs, was associated with hepatic morphologic and enzymatic alterations. This indicates that cannabinoids are possible hepatotoxic substances.