> [!note] > Pfizer product marketed as [Xeljanz](https://www.pfizer.com/products/product-detail/xeljanz). [[Janus Kinase|JAK]] inhibitor. **Tofacitinib**, sold under the brand **Xeljanz** among others, is a medication used to treat [rheumatoid arthritis](https://en.wikipedia.org/wiki/Rheumatoid_arthritis "Rheumatoid arthritis"), [psoriatic arthritis](https://en.wikipedia.org/wiki/Psoriatic_arthritis "Psoriatic arthritis"), and [ulcerative colitis](https://en.wikipedia.org/wiki/Ulcerative_colitis "Ulcerative colitis"). Common side effects include diarrhea, headache, and high blood pressure. Serious side effects may include infections, [cancer](https://en.wikipedia.org/wiki/Cancer "Cancer"), and [pulmonary embolism](https://en.wikipedia.org/wiki/Pulmonary_embolism "Pulmonary embolism"). In 2019, the safety committee of the [European Medicines Agency](https://en.wikipedia.org/wiki/European_Medicines_Agency "European Medicines Agency") began a review of tofacitinib and recommended that doctors temporarily not prescribe the 10 mg twice-daily dose to people at high risk for pulmonary embolism. The U.S. [Food and Drug Administration](https://en.wikipedia.org/wiki/Food_and_Drug_Administration "Food and Drug Administration") (FDA) also released warnings about the risk of blood clots. An important side effect of Jakinibs is serious bacterial, mycobacterial, fungal and viral infections. In the phase 3 trials of tofacitinib among opportunistic infections, pulmonary tuberculosis (TB) was reported in 3 cases all of which were initially negative upon screening for TB. It is in the [janus kinase](https://en.wikipedia.org/wiki/Janus_kinase "Janus kinase") (JAK) inhibitor class) [discovered](https://en.wikipedia.org/wiki/Drug_discovery "Drug discovery") and [developed](https://en.wikipedia.org/wiki/Drug_development "Drug development") by the [National Institutes of Health](https://en.wikipedia.org/wiki/National_Institutes_of_Health "National Institutes of Health") and [Pfizer](https://en.wikipedia.org/wiki/Pfizer "Pfizer"). Tofacitinib is a small molecule, not a biologic. As of June 2021, tofacitinib is available as a [generic medicine](https://en.wikipedia.org/wiki/Generic_medicine "Generic medicine") in the US.