After the treatment, the man grew a full head of hair, eyebrows, eyelashes, armpit, facial and other hair on various parts of his body.
There is currently no cure or long-term treatment for alopecia universalis, the disease that left the patient bare of hair, researchers said.
This is the first reported case of a successful targeted treatment for the rare, highly visible disease.
"The results are exactly what we hoped for," said Brett A King, assistant professor of dermatology at Yale University School of Medicine and senior author of the research paper.
"This is a huge step forward in the treatment of patients with this condition. While it's one case, we anticipated the successful treatment of this man based on our current understanding of the disease and the drug. We believe the same results will be duplicated in other patients, and we plan to try," said King.
The patient had previously been diagnosed with both alopecia universalis, a disease that results in loss of all body hair, and plaque psoriasis, a condition characterised by scaly red areas of skin.
The only hair on his body was within the psoriasis plaques on his head. He was referred to Yale Dermatology for treatment of the psoriasis. The alopecia universalis had never been treated.
King believed it might be possible to address both diseases simultaneously using an existing FDA-approved drug for rheumatoid arthritis called tofacitinib citrate.
The drug had been used successfully for treating psoriasis in humans. It had also reversed alopecia areata, a less extreme form of alopecia, in mice.
"There are no good options for long-term treatment of alopecia universalis. The best available science suggested this might work, and it has," said King.
After two months on tofacitinib at 10 mg daily, the patient's psoriasis showed some improvement, and the man had grown scalp and facial hair the first hair he'd grown there in seven years.
After three more months of therapy at 15 mg daily, the patient had completely regrown scalp hair and also had clearly visible eyebrows, eyelashes, and facial hair, as well as armpit and other hair, the doctors said.
"By eight months there was full regrowth of hair. The patient has reported feeling no side effects, and we've seen no lab test abnormalities, either," said co-author Brittany G Craiglow.
Tofacitinib appears to spur hair regrowth in a patient with alopecia universalis by turning off the immune system attack on hair follicles that is prompted by the disease, King said.
The research was published in the Journal of Investigative Dermatology.