While these drugs are excluded from basic Part D coverage, drug plans can include them as a supplemental benefit, provided they otherwise meet the definition of a Part D drug. However plans that cover excluded drugs are not allowed to pass on those costs to Medicare, and plans are required to repay CMS if they are found to have billed Medicare in these cases. Part D plans may cover all benzodiazepines and those barbiturates used in the treatment of epilepsy, cancer or a chronic health disorder. These two drug classes were originally excluded, until their reassignment in 2008 by the Medicare Improvements for Patients and Providers Act.