An arthritis drug has shown strong results for severe hair loss in two large trials, researchers reported on Monday.

Upadacitinib, already used for rheumatoid arthritis, was tested in about 1,400 people aged 12 to 64 with severe alopecia. At 24 weeks, 44 percent of those on the lower dose and 55 percent on the higher dose had at least 80 percent scalp hair coverage.

Up to 22.5 percent of participants on the higher dose regrew nearly all their hair, according to the results published in JAMA Dermatology.

Side effects included acne and common colds. The trials were funded by the drug’s maker, and experts say the results are promising but the treatment would be long-term.

Alopecia areata is an autoimmune condition that causes patchy or total hair loss. Current treatments are limited, and severe cases are hard to treat. Upadacitinib blocks inflammation signals linked to hair follicle damage. Regulators will review the trial data before deciding whether to approve it for alopecia.