O bjecti ve• He rbalists claim that the polypharmacy of botanical remedies provides 2 advantages over single-ingredient drugs:(1) prima ry active ingredients in herbs are synergized by secondary compounds, and (2) secondary compounds mitigate the side effects caused by primary active ingredients. To examine this second claim, medical marijuana was compared with its primary active ingredient, tetrahydrocannabinol.

Data Sources• A search on MEDLINE (1966-1999), AGRICOLA (19 90-1999), and Biological and Agricultural Index (1964-19 9 9) using keywords “cannabinoids,”“marijuana,”“tetra hyd ro cannab inol,”“Cannabis,” and “hemp.” Phytochemical and ethnobotanical data were searched with the Agricultural Research Service database. Unindexed botanical journals were scanned by hand. Study Selection• Studies documenting the efficacy of secondary compounds mitigating side effects of tetrahydrocannabinol consisting of double-blind trials, unblinded studies, animal models, and in vitro experiments.