From the Guidelines
Finasteride can cause decreased libido and erectile dysfunction due to its inhibition of the 5-alpha reductase enzyme, which converts testosterone to dihydrotestosterone (DHT), a potent androgen that plays a significant role in male sexual function and development. This reduction in DHT levels affects neurosteroid production in the brain, particularly allopregnanolone, which influences sexual desire and function 1. Additionally, the hormonal changes can impact nitric oxide production, which is essential for achieving and maintaining erections.
The evidence suggests that these side effects occur in approximately 2-5% of men taking the medication, though some studies suggest higher rates 1. The sexual side effects may persist even after discontinuing the medication in some individuals, a phenomenon called Post-Finasteride Syndrome.
- Key points to consider:
- Finasteride blocks the conversion of testosterone to DHT, leading to a 70% drop in DHT levels 1
- This reduction affects neurosteroid production, particularly allopregnanolone, which influences sexual desire and function
- Hormonal changes can impact nitric oxide production, essential for achieving and maintaining erections
- Side effects occur in approximately 2-5% of men taking the medication, with some studies suggesting higher rates
- Sexual side effects may persist even after discontinuing the medication in some individuals
If experiencing these side effects, patients should consult their healthcare provider before stopping the medication, as alternative treatments or dosage adjustments might be considered 1. It is essential to weigh the benefits of finasteride against the potential risks and side effects, particularly in patients with a history of sexual dysfunction or other underlying medical conditions.
From the FDA Drug Label
The most frequently reported adverse reactions were related to sexual function. 3.7% (57 patients) treated with finasteride tablets and 2. 1% (32 patients) treated with placebo discontinued therapy as a result of adverse reactions related to sexual function, which are the most frequently reported adverse reactions Table 1 presents the only clinical adverse reactions considered possibly, probably or definitely drug related by the investigator, for which the incidence on finasteride was ≥1% and greater than placebo over the 4 years of the study. In years 2 to 4 of the study, there was no significant difference between treatment groups in the incidences of impotence, decreased libido and ejaculation disorder Table 1: Impotence 8.1 3.7 5.1 5.1 Decreased Libido 6.4 3.4 2.6 2.6
The exact reason why finasteride causes a decrease in libido and erections is not explicitly stated in the drug label. However, it is reported that decreased libido and impotence are common adverse reactions associated with finasteride treatment, with incidence rates of 6.4% and 8.1%, respectively, in the first year of the study 2.
- Key points:
- Finasteride is associated with sexual dysfunction, including decreased libido and impotence.
- The exact mechanism by which finasteride causes these adverse reactions is not specified in the drug label.
From the Research
Mechanism of Finasteride-Induced Sexual Dysfunction
- Finasteride, a 5-alpha reductase inhibitor (5α-RI), is used to treat benign prostatic hyperplasia (BPH) and male androgenetic alopecia (MAA) 3.
- The medication works by inhibiting the conversion of testosterone to dihydrotestosterone (DHT), a potent androgen that plays a crucial role in male sexual function 3.
- The reduction in DHT levels is thought to contribute to the development of sexual dysfunction, including decreased libido and erectile dysfunction, in some patients taking finasteride 3, 4.
Prevalence of Sexual Dysfunction
- Studies have reported varying rates of sexual dysfunction associated with finasteride use, ranging from 2.1% to 15.8% for erectile dysfunction and 2.1% to 10.9% for decreased libido 5, 6.
- A review of clinical studies found that finasteride was correlated with erectile dysfunction in patients with BPH, but not in those with MAA 3.
- However, some studies have reported that finasteride can cause persistent sexual dysfunction, including decreased libido and erectile dysfunction, even after discontinuation of the medication 7, 6.
Nocebo Effect
- The nocebo effect, a phenomenon in which patients experience adverse effects due to their expectations or beliefs about a medication, may contribute to the development of sexual dysfunction in some patients taking finasteride 5.
- A study found that patients who were informed about the potential sexual side effects of finasteride were more likely to experience these effects than those who were not informed 5.
Persistent Sexual Dysfunction
- Some studies have reported that finasteride can cause persistent sexual dysfunction, including decreased libido and erectile dysfunction, even after discontinuation of the medication 7, 6.
- A study found that 96% of patients who experienced persistent sexual side effects associated with finasteride still had these symptoms after 9-16 months of follow-up 7.
- The exact mechanisms underlying persistent sexual dysfunction associated with finasteride are not fully understood and require further research 7, 6.