"It's Not Lupus" is a running-gag catchphrase from the Fox medical drama House, delivered by Hugh Laurie's character Dr. Gregory House whenever one of his junior diagnosticians floats lupus as a possible answer to a baffling case1. The line reads as both a diagnostic dismissal and a character tic, because House almost always rules the disease out before the team even finishes writing it on the whiteboard3.

Lupus, or Systemic Lupus Erythematosus, is a real autoimmune disease that attacks healthy tissue and mostly affects women between roughly 20 and 40 years old2. Its symptoms overlap with a long list of other conditions, which is exactly why the House writers kept it in play as a red herring and why the line landed as a joke inside the show's diagnostic-mystery formula2.

The catchphrase is typically used two ways online. In House-specific image macros, a still of Dr. House gets paired with a setup line about a mystery illness and the punchline "It's Not Lupus" (or the harder variant, "It's Never Lupus"). Outside House fandom, people often drop the line as a reply whenever someone floats an unlikely diagnosis or an obvious wrong answer, medical or not.