Ritlecitinib is a JAK inhibitor medicine for the treatment of severe alopecia areata (AA) in people aged 12 years and over. Severe AA means that someone has more than 50% scalp hair loss because of this autoimmune condition.

Its commercial brand name is Litfulo®, and it is produced by Pfizer. The recommended dose is usually 50mg to be taken once per day, in tablet form, by mouth.

A large clinical trial was done from 2018 to 2021, in which a total of 718 people affected by severe AA took part. Clinical trials are research studies to test how well the medicine works and how safe it is (more information about clinical trials). This trial was called Allegro-2b/3.

Clinical trial results

The amount of hair loss that people had at the start of the trial varied from person to person, but on average they had 88-93% scalp hair loss. Almost half (46%) of the participants had 100% scalp hair loss (alopecia totalis or universalis) at the start, and 15% were adolescents (aged 12-17). The duration of their ‘current episode’ of hair loss was on average 3.5 years, although this ranged from 6 months up to 10 years. People with a ‘current episode’ longer than 10 years were not included in the trial.

Participants received the study medicine for 24 weeks. They were randomly assigned to receive ritlecitinib 50 mg, ritlecitinib 30 mg, or placebo. Some people also received a 200 mg ‘loading dose’ of ritlecitinib for 4 weeks beforehand. At the end of the 24 weeks, the results were as follows:

• On 50 mg ritlecitinib, with the 200 mg ‘loading dose’, 31% of people reached a point where at least 80% of their scalp had hair growth.
• On 50 mg ritlecitinib, without the 200 mg ‘loading dose’, 23% of people reached at least 80% scalp hair growth.
• On 30 mg ritlecitinib, with the 200 mg ‘loading dose’, 22% of people reached at least 80% scalp hair growth.
• On 30 mg ritlecitinib, without the 200 mg ‘loading dose’ 14% of people reached at least 80% scalp hair growth.
• On placebo, 2% of people reached at least 80% scalp hair growth.

After the initial 24 weeks, a second 24 week ‘extension period’ followed in which those on ritlecitinib continued on the same dose. Those who had received placebo before now switched to 50 mg, with or without a 200 mg loading dose for 4 weeks.

• Of those who had received the loading dose, then continued on 50 mg, 40% reached a point where at least 80% of their scalp had hair growth.
• Of those who had continued on 50 mg (without loading dose), 43% reached at least 80% scalp hair growth.
• Of those who had received the loading dose, then continued on 30 mg, 34% reached at least 80% scalp hair growth.
• Of those who continued on 30 mg (without loading dose), 31% reached at least 80% scalp hair growth.
• Of those who switched from placebo to a 200 mg loading dose, then 50 mg ritlecitinib, 34% reached a point where more than 80% of their scalp had hair growth.
• Of those who switched from placebo to 50 mg ritlecitinib, 19% reached a point where more than 80% of their scalp had hair growth.

A graphical summary of the ritlecitinib trial data is available via The Lancet.

What adverse events did people experience? 

During clinical trials, all negative health effects that happen are recorded. These are called ‘adverse events’. These are different from side effects, because it can not always be determined if they happen because of the medicine, or would have happened anyway. For example, people may have been infected by the flu or COVID, or experienced headaches, and it is not clear if this was because of the medicine.

• Adverse events were experienced by 80-86% of participants across all different treatment groups, of which most were mild or moderate in severity. 
• The most common adverse events were upper respiratory tract infection in 3-12% of participants, common cold in 6-14% of participants, and headache in 8-18% of participants.
• People experienced similar adverse events across all groups, although influenza, upper respiratory tract infection, and urinary tract infection, were reported more often in the 200 mg + 50 mg ritlecitinib group.
• Folliculitis, urticaria, and dizziness were reported more often in the 200 mg + 50 mg and 200 mg + 30 mg groups.
• Serious adverse events were seen in 3 people on placebo, 1 on 30 mg ritlecitinib, and 4 on 200 mg + 50 mg ritlecitinib.
• 2-3% of people on ritlecitinib, and 2% of people on placebo, stopped the study because of adverse events.
• Two people experienced breast cancer during the study, of which one was thought to be related to the study medicine (in the 50 mg group), and one was not (in the 200 mg + 50 mg group).
• No deaths, major cardiovascular events, or opportunistic infections were reported.

Results in adolescents (aged 12-17)

A separate analysis of the data for 105 adolescent participants showed that after 48 weeks:

• On 200 mg + 50 mg ritlecitinib, 25% reached at least 80% scalp hair growth.
• On 200 mg + 30 mg ritlecitinib, 39% reached at least 80% scalp hair growth.
• On 50 mg ritlecitinib, 50% reached at least 80% scalp hair growth.
• On 30 mg ritlecitinib, 26% reached at least 80% scalp hair growth.
• Of those who had received placebo then switched to 200 + 50 mg, 40% reached at least 80% scalp hair growth.
• Of those who had received placebo then switched to 200 mg + 30 mg, 33% reached at least 80% scalp hair growth.

The most common adverse events were headaches, acne, and the common cold. Two people on ritlecitinib stopped the study because of adverse events. No deaths, malignancies (cancers), major adverse cardiovascular events, pulmonary embolisms, opportunistic infections, or herpes zoster infections were reported in adolescents.

Further research

A clinical trial to test the safety and effectiveness of ritlecitinib in children with severe alopecia areata, aged 6-12 years of age, started in 2025 and is ongoing.

A long-term study testing ritlecitinib in the real-world setting (PRESTO) started in 2024 is also ongoing.

Full research articles

The full results from the Allegro-2b/3 trial were published in The Lancet. 

The results for adolescents from the Allegro-2b/3 trial were published in the journal Pediatric Dermatology.