1. An illicit substance one is addicted to or tends to prefer. I dabbled with a few different recreational drugs in college, but marijuana was my drug of choice.

2. The favored pharmaceutical treatment for a given medical condition or ailment. Lithium has long been the drug of choice for many physicians to treat depression and bipolar disorder.

3. By extension, any habit, activity, or vice that one is particularly fond of or dependent upon. A lot of people resort to drugs or alcohol to cope with their problems, but exercise has always been my drug of choice. Coffee became my drug of choice after working as a barista for three years during college.