For more than half a century, marijuana has been considered a Schedule I drug, classified on the same level as highly addictive substances like heroin that the Drug Enforcement Administration describes as having no currently accepted medical use. Moving marijuana to Schedule III, as the Department of Health and Human Services recommended in August, would put it alongside less addictive substances like Tylenol with codeine, ketamine and testosterone, meaning that it would be subject to fewer restrictions on production and research, and that eventually it could be prescribed by a doctor.