Glossary

JAK inhibitor (Janus kinase inhibitor)

A class of immunomodulator drugs that block JAK-STAT signalling in immune cells. Three are FDA-approved for severe alopecia areata: baricitinib (2022), ritlecitinib (2023), deuruxolitinib (2024).

Also: JAKi

JAK inhibitors (JAKi) are oral immunomodulator drugs that block Janus kinase signalling, an intracellular pathway that mediates many cytokine effects in immune cells. By dampening this pathway, JAK inhibitors reduce the autoimmune attack on hair follicles in alopecia areata.

Three are now FDA-approved for severe alopecia areata:

Baricitinib (Olumiant), 2022. Adults with severe AA.
Ritlecitinib (Litfulo), 2023. Patients 12 and over with severe AA.
Deuruxolitinib (Leqselvi), 2024. Adults with severe AA.

Roughly a third of patients with severe AA achieve significant scalp hair regrowth (at least 80% coverage from a baseline of less than 50%) over 36 to 52 weeks of treatment. Eyebrow and eyelash regrowth is also documented.

Stopping leads to relapse in most patients. Long-term treatment is generally required to maintain regrowth.

Class boxed warning: serious infections, malignancy, major cardiovascular events, and thrombosis. Pre-treatment workup includes TB and hepatitis screening and a baseline lipid panel; routine monitoring is standard. The risk-benefit conversation with a dermatologist is essential, especially in younger patients.