Per IRS Publication 502 Medical and Dental Expenses (Including the Health Coverage Tax Credit), page 5:

Alcoholism

You can include in medical expenses amounts you pay for an inpatient's treatment at a therapeutic center for alcohol addiction. This includes meals and lodging provided by the center during treatment.

You can also include in medical expenses amounts you pay for transportation to and from Alcoholics Anonymous meetings in your community if the attendance is pursuant to medical advice that membership in Alcoholics Anonymous is necessary for the treatment of a disease involving the excessive use of alcoholic liquors.

Page 7:

Drug Addiction

You can include in medical expenses amounts you pay for an inpatient's treatment at a therapeutic center for drug addiction. This includes meals and lodging at the center during treatment.

Note that any link in the information above is updated each year automatically and will take you to the most recent version of the webpage or document at the time it is accessed.