Objective: To review the legal status of medical marijuana in the US. Data Sources: Relevant publications were located using LexisNexis (1982–October 2006), WestLaw (1996–October 2006), BNA Health Law Reporter (1996–October 2006), MEDLINE (1996–October 2006), EMBASE (1980–October 2006), International Pharmaceutical Abstracts (1970–October 2006), and an Internet search targeting government sites using the key words medical marijuana. Study Selection and Data Extraction: Federal and state medical marijuana laws were examined. Relevant cannabinoid-based drug products were reviewed. Federal and State Supreme Court and Appeal level cases involving medical marijuana were evaluated. Data Synthesis: Marijuana is regulated as a Schedule I controlled substance and its use is prohibited under federal law. Dronabinol and nabilone are synthetic cannabinoids approved by the Food and Drug Administration and Sativex is a cannabis-based extract being evaluated in Phase III trials. The federal government sponsors a single patient compassionate use Investigational New Drug Application program providing medical marijuana for a small number of patients. Eleven states permit marijuana use for medical purposes and one state provides a defense of medical necessity. Employers do not have to provide workplace accommodations for employees using medical marijuana and can terminate them at will. Healthcare providers have First Amendment constitutional protections that allow them to discuss marijuana with patients. Conclusions: Until the Supreme Court rules directly on the constitutionality of state medical marijuana laws, a conflict remains. Marijuana use remains illegal under federal law and states assume their medical marijuana laws to be constitutional.