Baricitinib

What it is

Baricitinib is an oral drug that blocks two Janus kinase enzymes (JAK1 and JAK2). It was first approved for rheumatoid arthritis and is made by Eli Lilly. In 2022 it became the first treatment ever approved for severe alopecia areata, an autoimmune condition where the immune system attacks hair follicles (see alopecia areata). It is not a treatment for ordinary male or female pattern hair loss; see JAK inhibitors and hair.

• US: approved in June 2022 for adults with severe alopecia areata, and extended in September 2026 to adolescents aged 12 and over. Prescription-only with a boxed warning.
• EU: authorised for severe alopecia areata in adults and adolescents aged 12 and over (EMA).
• UK: licensed, but NICE did not recommend it for severe alopecia areata on the NHS in October 2023 because cost-effectiveness was above its threshold. The NHS-funded option in England is ritlecitinib.

How it works

In alopecia areata, T cells attack the hair bulb, driven by interferon-gamma and related signals that all pass through JAK enzymes. Blocking JAKs reversed established disease in mice, and three patients on the related drug ruxolitinib regrew nearly all their hair within 5 months (Xing 2014). Baricitinib interrupts the same signalling, so follicles leave the resting phase and regrow hair. It suppresses the attack; it does not cure the tendency to it.

What the studies show

• In a 110-person phase 2 trial, 51.9% on 4 mg, 33.3% on 2 mg and 3.6% on placebo had at least 80% scalp hair at week 36 (King 2021).
• Two phase 3 trials (654 and 546 adults) found at least 80% scalp hair at week 36 in 38.8% (4 mg), 22.8% (2 mg) and 6.2% (placebo) in the first, and 35.9%, 19.4% and 3.3% in the second. All were funded by Lilly (King 2022). The US label uses stricter counting and reports slightly lower figures (label).
• Response kept rising: at week 52, 40.9% (4 mg) and 21.2% (2 mg) had at least 80% scalp hair in the first trial (Kwon 2023). About 90% of week-52 responders still had it at week 104 (Senna 2024), and 89.1% (4 mg) and 83.6% (2 mg) at week 152 (Senna 2026).
• Stopping loses the benefit: by week 152, 80% of responders switched to placebo had lost it versus 7% who stayed on the drug; retreatment recaptured response in most (King 2024).
• Eyebrows and eyelashes often return with the scalp: week-36 response was 44.3% versus 12.6% for eyebrows and 46.4% versus 12.4% for eyelashes (Mostaghimi 2025).
• A Cochrane review of 63 trials (4,817 people) found baricitinib was the only alopecia areata treatment with high-certainty evidence of benefit (Mateos-Haro 2023).
• There is no head-to-head trial against other JAK inhibitors; an indirect comparison found no clear difference between ritlecitinib 50 mg and baricitinib 4 mg at week 24 (Aceituno 2025).
• No trial of baricitinib in pattern hair loss exists.

How it's used in studies

• Trials used 2 mg or 4 mg once daily in adults with at least 50% scalp loss for at least 6 months.
• The US label starts at 2 mg once daily and increases to 4 mg if response is inadequate; for nearly complete scalp loss 4 mg may be used first, then reduced once response is adequate. It is not recommended with other JAK inhibitors or potent immunosuppressants such as cyclosporine (label).
• Judging failure at 3 to 6 months is too early for many people. Treatment is open-ended.

Side effects and safety

• Common in alopecia areata trials: acne, raised creatine kinase and cholesterol, upper respiratory infections, headache and urinary tract infections. A 2025 network meta-analysis found baricitinib more likely than other oral JAK inhibitors to cause acne (RR 4.66), urinary infection (RR 2.72) and high lipids (RR 1.77) (Qi 2025).
• Boxed warning (US): serious infections, death, cancer, major cardiovascular events and blood clots, carried over from the whole class after a tofacitinib trial in older people with rheumatoid arthritis (Ytterberg 2022).
• EU restrictions: in people aged 65 and over, those with cardiovascular risk factors and those at raised cancer risk, use only if there is no suitable alternative. Do not use in pregnancy; contraception is needed during treatment (EMA).
• Long-term alopecia areata data are reassuring so far: serious adverse events 2.6 per 100 patient-years and shingles 1.9 per 100 patient-years over up to 4 years, in a young, healthy trial population (King 2025).
• Screening (tuberculosis, blood counts, lipids, liver, kidney) is needed under a dermatologist.

Bottom line

Baricitinib suits people with severe alopecia areata, roughly half or more of the scalp bare. About one in three on 4 mg reach at least 80% scalp coverage within 9 to 12 months, brows and lashes often return, and the benefit lasts only while taking it. It does nothing proven for pattern thinning, diffuse shedding or cosmetic concerns. The US list price at approval was about $2,497 per 30 days. Discuss with a doctor.

Fun facts

• Stop it, and the hair goes: in the randomised withdrawal arm, 80% of people who had regrown their hair lost the benefit on placebo, against 7% who stayed on the drug (King 2024).