Gregory House is addicted to Vicodin in House M.D.
Vicodin is a brand name for a prescription combination of hydrocodone and paracetamol, also known as acetaminophen. In the series, House uses it to manage severe chronic leg pain caused by an infarction in his quadriceps muscle.
His dependence is a continuing storyline rather than a minor character detail. It affects his judgment, employment, relationships, and willingness to accept medical or psychological help. Several arcs depict attempts to stop using the drug and the consequences of relapse.
Vicodin is sometimes remembered simply as House’s “pain medicine,” but the specific answer is the brand name. The show also uses his addiction to complicate the image of a doctor whose diagnostic intelligence does not protect him from illness or dependency.