The revelation by his longtime doctor that President Trump takes a medication to prevent hair loss has piqued curiosity about the drug.
In an interview with The New York Times, the physician, Dr. Harold N. Bornstein, said that Mr. Trump takes finasteride, also marketed as Propecia.
The drug, a one-a-day pill, is a popular treatment for so-called male-pattern hair loss, in which the hairline recedes and hair thins at the temples and crown, sometimes to the point of leaving just a horseshoe-shaped fringe around the sides and the back of the head.
The culprit in this type of baldness is a male hormone, dihydrotestosterone or DHT. In some men, hair follicles are particularly sensitive to it, probably based on genetics. DHT forms when an enzyme converts testosterone into it; finasteride blocks the enzyme, lowering DHT levels.
The drug is better at stopping hair loss than at bringing back what’s already gone.
“I set expectations from the beginning, realistic expectations” about the drug, said Dr. Andrew Alexis, the chairman of the dermatology department at Mount Sinai St. Luke’s and Mount Sinai West in New York. “The thing I emphasize the most is stopping progression and preserving the hair you have. I think it’s very successful at doing that. “
Dr. Alexis is not involved with Mr. Trump’s care.
Most men with this type of hair loss start treatment with a different drug, minoxidil, also sold as Rogaine, which is rubbed into the scalp, Dr. Alexis said. If they do not see enough of an effect, they can add finasteride. Many of his patients wind up using both drugs, Dr. Alexis said. The treatment works best on the top of the head, and not as well at the temples and the receding hairline.