It's Not Lupus is a catchphrase from the television show House. The series revolves around the unconventional and misanthropic genius, doctor Gregory House, working with younger doctors at the Princeton‑Plainsboro Teaching Hospital (PPTH) in New Jersey, in order to solve difficult health mysteries. The phrase was coined when the younger doctors were suggesting a case of the auto-immune disease lupus when they couldn't figure out what was wrong with the patient. Because lupus usually takes several years to be diagnosed, Dr. House usually says "It's not lupus." or "It's never lupus." The phrase was a popular meme during the show's peak in popularity during the 2000s.
In House, which ran from 2004-2012, the titular doctor's team usually encounters cases where they must figure out what is wrong with a patient. Several times a patient displayed symptoms consistent with lupus, leading one of House's younger staff members to suggest that could be the reason the patient is ill. House usually counters the doctor with some variation of "It's not lupus." On April 9th, 2010, YouTube account Camilladilla posted a compilation of times the cast suggested diagnosing a patient with lupus, which House resists.
During the peak of the show's popularity in the 2000s, the phrase "It's not lupus" was commonly used in image macros involving House. For example, an Advice Animal of Dr. House saw many iterations featuring the catchphrase (examples shown below).
The phrase was a running gag on the show until a season 4 episode when a patient actually did have lupus. In 2011, The Conversation ran an article explaining why House was always sure it was never lupus, writing that lupus was difficult to diagnose due to its wide variety of symptoms. "Initial and chronic lupus symptoms mimic the symptoms of several other diseases, leading to misdiagnoses and making lupus extremely challenging to diagnose," they wrote. In 2016, Buzzfeed ran a listicle compiling 29 times it "wasn't lupus" on House.