The central finding of a 2004 study led by Italian researcher Dr. Antonella Tosti, in which he and his team investigated sexual dysfunction in hair loss patients being treated for androgenetic alopecia, was that there was no statistically significant change in sexual function after four to six months of treatment with finasteride 1mg (Propecia).
The researchers used a questionnaire, called the abridged 5-item version of the International Index of Erectile Function (IIEF-5), to measure sexual function in the men in the study. The questionnaire, which is considered an internationally valid diagnostic tool for distinguishing between men with and without erectile dysfunction, asks the patients 15 questions on the topics of: erectile function, orgasmic function, sexual desire, intercourse satisfaction, and overall sexual satisfaction. By administering the questionnaire both before and after treatment with finasteride, the researchers were able to determine if sexual function was impaired by the treatment.
The result of this investigation in the sexual function of 186 patients was that, “the erectile function of all patients remained stable after 4 to 6 months of treatment with finasteride 1 mg.”
Interestingly, the research team found that sexual side effects were actually less common than reported in the clinical trials of the drug. They suggest that this difference was potentially due to the fact that subjects in the clinical trials were made aware of the potential for sexual side effects, and were asked about these side effects upon each visit, which led to higher reporting of side effects than what would otherwise be the case.
Reference:
Tosti A, Pazzaglia M, Soli M, Rossi A, Rebora A, Atzori L, Barbareschi M, Benci M, Voudouris S, Vena GA. Evaluation of Sexual Function With an International Index of Erectile Function in Subjects Taking Finasteride for Androgenetic Alopecia. Arch Dermatol. 2004;140:857-858.
Download the Tosti study of erectile function and finasteride 
