Pub 502

Medicines and Drugs

   You can include in medical expenses amounts you pay for prescribed medicines
   and drugs. A prescribed drug is one that requires a prescription by a doctor for its
   use by an individual. You can also include amounts you pay for insulin. Except for
   insulin, you cannot include in medical expenses amounts you pay for a drug that is
   not prescribed. 

   Controlled substances. You cannot include in medical expenses amounts you pay
   for controlled substances (such as marijuana) in violation of federal law.