What are the side effects of Finasteride (Dutasteride)?

From the Guidelines

Finasteride is associated with a higher frequency of adverse events, including erectile dysfunction, gynecomastia, and decreased libido, which occur in approximately 2-4% of men taking the medication. These side effects are consistently reported in studies, including the 2009 American Society of Clinical Oncology/American Urological Association clinical practice guideline 1. The guideline notes that virtually all randomized controlled trials (RCTs) show an increase in reported erectile dysfunction and gynecomastia, as well as decreases in ejaculate volume and libido, in the treatment arm. Some key points to consider include:

• Decreased libido, erectile dysfunction, and gynecomastia are the most common side effects, occurring in 2-4% of men taking finasteride 1
• Decreases in ejaculate volume are also common, although the exact frequency is not specified in the guideline 1
• The sexual dysfunction associated with finasteride decreases over time, although it remains statistically significant 1
• The magnitude of effect on sexual functioning is smaller than natural sources of variability in the study population, with a mean difference of 3.21 points on a scale of 0 to 100 1
• Discontinuation rates due to adverse events are approximately 6% in both the finasteride and placebo arms 1. Some men may experience other side effects, such as depression, anxiety, or cognitive changes, although these are not as well-studied as the sexual side effects. Physical side effects, including skin rash, itching, and allergic reactions, are rare. If you experience troublesome side effects, it is essential to consult your healthcare provider before stopping the medication, as they may recommend dosage adjustments or alternative treatments.

From the FDA Drug Label

The most frequently reported adverse reactions were related to sexual function. 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. Table 1: Drug-Related Adverse Experiences Year 1 (%) Years 2,3 and 4*(%) Finasteride Placebo Finasteride Placebo Impotence 8.1 3.7 5.1 5.1 Decreased Libido 6.4 3.4 2.6 2.6 Decreased Volume of Ejaculate 3.7 0.8 1.5 0.5 Ejaculation Disorder 0.8 0.1 0.2 0.1 Breast Enlargement 0.5 0.1 1.8 1.1 Breast Tenderness 0.4 0.1 0.7 0.3 Rash 0.5 0.2 0.5 0. 1 The individual adverse effects which occurred more frequently in the combination group compared to either drug alone were: asthenia, postural hypotension, peripheral edema, dizziness, decreased libido, rhinitis, abnormal ejaculation, impotence and abnormal sexual function

The side effects of Finasteride include:

• Impingard actions: Impingard, Impingard
• Impingard
• Sexual function related side effects:
  • Impotence
  • Decreased libido
  • Decreased volume of ejaculate
  • Ejaculation disorder
• Other side effects:
  • Breast enlargement
  • Breast tenderness
  • Rash
  • Asthenia
  • Postural hypotension
  • Peripheral edema
  • Dizziness
  • Rhinitis
  • Abnormal ejaculation
  • Abnormal sexual function 2

From the Research

Side Effects of Finasteride

• The most commonly reported side effects of finasteride include:
  • Erectile dysfunction 3, 4, 5, 6
  • Decreased libido 3, 4, 5, 6
  • Male infertility 3
  • Ejaculation problems 3
  • Loss of libido 3
  • Depression 5, 6
  • Decreased alcohol consumption 5
• These side effects may persist despite discontinuation of the medication 4, 5
• The severity and persistence of side effects of finasteride are still a topic of controversy 3
• Some studies suggest that finasteride may be associated with permanent sexual dysfunction 4
• Patients should be educated about the possible short- and long-term side effects of finasteride 6, 7

Mechanism of Side Effects

• Finasteride works by inhibiting the 5-alpha reductase enzyme, which converts testosterone to dihydrotestosterone (DHT) 3
• DHT is an important androgen in both human and animal studies, and low levels of DHT may be related to erectile dysfunction 5
• Finasteride may also affect neurosteroids, such as allopregnanolone, which have been linked to depression and decreased alcohol consumption 5

Prevalence of Side Effects

• The prevalence of side effects varies depending on the study, but most studies report that a significant percentage of patients experience some type of sexual side effect 3, 4, 5, 6
• One study found that 96% of subjects with persistent sexual side effects continued to experience them after 9-16 months 4
• Another study found that 89% of subjects met the definition of sexual dysfunction according to the Arizona Sexual Experience Scale (ASEX) 4