Donald Trump takes small doses of the drug finasteride to treat male pattern baldness, the president's former physician told the New York Times.

The drug has been associated with sexual dysfunction and depression.

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The revelation that Trump uses a prostate-related drug to grow scalp hair appears to explain why Trump has a very low level of prostate specific antigen, or PSA, a marker sometimes used to diagnose prostate cancer, the Times reported after interviewing Dr. Harold N. Bornstein.

Bornstein, 69, credited the drug with helping him keep his own shoulder-length locks.

"[Trump] has all his hair," Bornstein said. "I have all my hair."

However the drug is associated with several negative side effects, including mental confusion and impotence.

According to a 2003 study published in science journal Urology, 15% of the men on finasteride suffered sexual side effects, compared with only 7% of the men on placebos.

Since 2011, approximately 1,245 lawsuits have been filed against Propecia's manufacturer, Merck, alleging that the company failed to warn users of a number of sexual and cognitive side effects.

Trump hair
Donald Trump's hair loss medication is associated with sexual dysfunction and mental confusion Getty Images

After Trump announced his candidacy for the presidency, Bornstein released a statement, in which he claimed "If elected, Mr. Trump, I can state unequivocally, will be the healthiest individual ever elected to the presidency." He later said he wrote the note in five minutes while in a limousine sent by Trump, which was waiting outside.

Bornstein claimed to have been Trump's personal physician since 1980 but admitted he had not had contact with Trump since the 2016 election.

He also stated that the president takes a handful of other medications, including daily aspirin to lower the risk of heart attack, an antibiotic to treat the skin condition rosacea, and a statin to lower cholesterol

The White House would not comment on the information provided by Dr Bornstein, and refused to confirm to the New York Times whether Dr Bornstein had been Trump's physician.