Ritlecitinib

What it is

Ritlecitinib is an oral kinase inhibitor from Pfizer that blocks JAK3 and the TEC family of kinases, a narrower target than baricitinib's JAK1 and JAK2. It is approved for severe alopecia areata in people aged 12 and older. It is not a treatment for pattern hair loss, and no trial in pattern hair loss was found; see JAK inhibitors and hair.

• US: approved 23 June 2023 at 50 mg daily for ages 12 and up. Prescription-only.
• EU: authorised in September 2023 for adults and adolescents aged 12 and over. Contraindicated in active serious infection (including tuberculosis), severe liver impairment, pregnancy and breastfeeding; stop if there is no improvement by 36 weeks (EMA).
• UK: licensed and recommended by NICE for use on the NHS in England, which describes it as the usual treatment among the JAK inhibitors.

How it works

Alopecia areata is driven by cytotoxic T cells and interferon-gamma and related cytokine signals that depend on JAK enzymes. Blocking JAKs reversed disease in mice and in three patients on ruxolitinib (Xing 2014). Ritlecitinib's JAK3 and TEC blockade hits both cytokine signalling and cytotoxic T-cell function.

What the studies show

• In 718 people aged 12 and over, 23% on 50 mg had at least 80% scalp hair at week 24 versus 2% on placebo (31% with a 200 mg loading dose first). Pfizer funded the trial (King 2023).
• In an open-label extension of 191 people on 50 mg, 65.1% had at least 80% scalp hair at 3 years (47.1% if missing data are counted as failures), and 88 to 90% of year-1 responders kept it. Female sex, less extensive and shorter hair loss predicted response (Senna 2026).
• An indirect comparison found no evidence of a difference between ritlecitinib 50 mg and baricitinib 4 mg at week 24, with wide uncertainty and Pfizer-affiliated authors (Aceituno 2025).
• Pooled safety across four studies (1,294 people, 2,092 patient-years): serious adverse events 4.4%, shingles 0.9 per 100 patient-years, major cardiovascular events 0.1 per 100 patient-years and two deaths (King 2024).
• Hair loss returns on stopping for many people, though relapse risk appears lower in acute-phase disease.

How it's used in studies

• 50 mg once daily is the approved dose. Trials tested 10, 30 and 50 mg with or without a 4-week 200 mg loading dose, for 24 weeks in the pivotal trial and extensions to 3 years (King 2023).

Side effects and safety

• Common in pivotal trials: headache (10.8%), diarrhoea (10%), acne (6.2%), rash (5.4%) and hives (4.6%).
• The EU label also lists folliculitis, dizziness and upper respiratory infections, with risk-minimisation measures for infections, cardiovascular disease, cancer, nerve toxicity and fetal harm (EMA).
• JAK-class warnings (serious infection, death, cancer, major cardiovascular events, clots) apply; see baricitinib.
• Pregnancy: not recommended; it is an EU contraindication.

Bottom line

For adolescents and adults with extensive severe alopecia areata, ritlecitinib is among the best-supported options, and in the US it was the only approved one for 12-year-olds at the time of writing. Expect around 1 in 4 to reach near-full scalp coverage at 6 months, more with time, as a continuing treatment rather than a cure. It is costly and specialist-supervised, with infection screening. It is irrelevant for ordinary pattern thinning, where minoxidil and finasteride apply. Discuss with a doctor.