Doctors conducted the pilot trial after identifying the immune cells responsible for destroying hair follicles in people with the condition.
Within four or five months of being put on the drug, ruxolitinib, all three patients experienced complete hair re-growth.
US lead researcher Dr Raphael Clynes, from Columbia University Medical Center in New York, said: “We’ve only begun testing the drug in patients, but if the drug continues to be successful and safe, it will have a dramatic positive impact on the lives of people with this disease.”
However, more research is needed before the drug can safely be used as a baldness treatment.
Alopecia is a common autoimmune disease that leads to partial or total hair loss. One of its best known sufferers is the Scottish former television presenter Gail Porter, who refuses to wear a hat or wig to hide her baldness.
The trial followed tests on mice using two new drugs known as JAK inhibitors that can be taken in pill form and block immune pathways.
Ruxolitinib is approved for the treatment of a form of bone marrow cancer in both the US and EU. The other drug, tofacitinib, is licensed for the treatment of rheumatoid arthritis in the US but not in Europe.
In mouse experiments, both drugs completely restored the hair of animals with alopecia within 12 weeks.
The trial patients all had moderate-to-severe alopecia areata, which causes patchy loss of hair.Each was given a 20 milligram dose of ruxolitinib twice a day. The drug’s effectiveness was linked to the disappearance of T-cell immune cells, which attack hair follicles in the scalp.
“We still need to do more testing to establish that ruxolitinib should be used in alopecia areata, but this is exciting news for patients and their physicians,” Dr Clynes said. “This disease has been completely understudied. Until now, only two small clinical trials evaluating targeted therapies in alopecia areata have been performed.”
Porter is affected by a more serious form of the condition called alopecia totalis, which results in complete baldness.
The research appears in the latest online edition of Nature Medicine journal.
Co-author Professor Angela Christiano, also from Columbia University, highlighted the devastating psychological effect alopecia can have.
“Patients with alopecia areata are suffering profoundly, and these findings mark a significant step forward for them,” she said. “The team is fully committed to advancing new therapies for patients with a vast unmet need.”
Professor David Bickers, a practising dermatologist at Columbia University, said: “This is a major step forward in improving the standard of care for patients suffering from this devastating disease.”