Using common hair regrowth drugs may have beneficial effects on the appearance of those suffering from male pattern hair loss, also known as alopecia, but this could lead to sexual side effects such as erectile dysfunction and loss of libido.

Some drugs prescribed for benign prostate enlargement (BPH) were also associated with similar unwanted effects.

In a new study, Abdulmaged Traish, from Boston University School of Medicine, and colleagues have found that 25 percent of men who currently take BPH treatment drugs finasteride (Proscar) or dutasteride (Avodart), do not seem to benefit from these medications.

Individuals who were prescribed Proscar (finasteride) or Avodart (dutasteride) for alopecia were also found to be at risk for the unwanted side effects caused by these drugs.

Finasteride and dutasteride belong to a family of drugs called 5a-reductase inhibitors, or 5a-RIs, which inhibits the conversion of testosterone to 5a-dihydrotestosterone (5a-DHT) and a number of other steroid hormones. Prostate volume decreases when the concentration of 5a-DHT is reduced, which then improves urinary flows.

Emerging clinical evidence provides strong indication that 5a-RIs are associated with unwanted sexual side effects.

Finasteride indicates in its package insert loss or reduced libido in a tenth of the patients. Eighteen percent reported erectile dysfunction, but the effects in some patients remain despite stopping the therapy.

The researchers said that the idea that the sexual side effects emerge early in the first six months of medication and then get back to baseline is not accurate.

In their study published in the journal Endocrine Reviews and Metabolic Disorders on Aug. 23, the researchers said that future studies should investigate why some patients are affected by these long-term adverse sexual side effects.

"Future studies should investigate the biochemical and physiological mechanisms that underlie the persistence of the adverse sexual side effects to determine why a subset of patients is afflicted with such persistence or irreversible adverse effects," the researchers wrote.

The researchers likewise said that research on the nonsexual side effects of the drugs such as diabetes, depression and psychosis could give a better understanding on the range of effects brought about by these medications.

"Inhibition of 5α-R activity may potentiate insulin resistance, Type 2 diabetes, vascular disease and osteoporosis, but studies have not been definitive," Traish said. "The investigation into psychiatric side effects of 5α-RIs has been limited, but some case series describe increased depression and anxiety symptoms among patients on the medication."

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