Adverse Structural and Functional Effects of Marijuana on the Brain: Evidence Reviewed

The growing use and legalization of cannabis are leading to increased exposures across all age groups, including in adolescence. The touting of its medicinal values stems from anecdotal reports related to treatment of a broad range of illnesses including epilepsy, multiple sclerosis, muscle spasms, arthritis, obesity, cancer, Alzheimer disease, Parkinson disease, post-traumatic stress, inflammatory bowel disease, and anxiety. However, anecdotal data and the high level of interest in this treatment must not obscure objective assessments of any potential and realized short- and long-term adverse effects of cannabis, particularly with respect to age of onset and chronicity of exposure. This critical review focuses on evidence-based research designed to assess both therapeutic benefits and harmful effects of cannabis exposure and is combined with an illustration of the neuropathologic findings in a fatal case of cannabis-induced psychosis. The literature and reported case provide strong evidence that chronic cannabis abuse causes cognitive impairment and damages the brain, particularly white matter, where cannabinoid 1 receptors abound. Contrary to popular perception, there are few objective data supporting preferential use of cannabis over conventional therapy for restoration of central nervous system structure and function in disease states such as multiple sclerosis, epilepsy, or schizophrenia. Additional research is needed to determine if subsets of individuals with various neurological and psychiatric diseases derive therapeutic benefits from cannabis.