Vicodin is the medication most associated with House's chronic leg pain and addiction in House M.D.
House takes Vicodin, a prescription combination of hydrocodone and acetaminophen, to manage severe pain caused by a past infarction in his right thigh. His dependence on the drug becomes a recurring medical, professional, and personal conflict throughout the series.
The medication is sometimes confused with other prescription drugs that appear in the show, including methadone and experimental treatments used during particular storylines. Vicodin remains the canonical answer because it is House's characteristic pain medication and a defining part of his initial characterization.