Does Finasteride affect muscle growth and muscle mass?

Finasteride 1mg tablets are one of the most commonly prescribed treatments for hair loss, particularly following a hair transplant. The 5 mg dose of Finasteride is commonly used to treat prostate gland enlargement, medically known as benign prostatic hyperplasia (BPH).

It works by blocking an enzyme called 5-alpha-reductase (5AR). This enzyme normally turns the hormone testosterone into a more potent chemical called Dihydrotestosterone (DHT). When this enzyme's action is stopped, DHT levels in the body go down. Too much DHT is linked to hair loss and other health issues, so reducing it results in clinical benefits.

How does Finasteride influence muscle development?

By blocking the conversion of testosterone to DHT, Finasteride increases the circulating levels of testosterone, which may signal more muscle growth. Testosterone also gets changed into oestrogen. Thus, the use of Finasteride in males can further shift the hormonal balance towards oestrogen excess(1). A question often asked is how Finasteride affects muscle growth and muscle mass.

What role does testosterone play in muscle mass maintenance?

Testosterone plays an important role in maintaining muscle mass, strength and overall physical development. It is the key hormone responsible for the growth of muscle tissue, particularly during puberty. In adults, testosterone continues to regulate muscle strength, and its levels are directly linked to the maintenance of muscle mass.

Low testosterone levels, which can result from ageing, health conditions, or other factors, may decrease muscle strength and mass(2). This issue is sometimes improved with testosterone replacement therapy but also by maintaining a healthy lifestyle, including regular exercise and a balanced diet.

What is the effect of Finasteride on muscle mass?

Theoretically, higher testosterone may contribute to higher muscle mass by inhibiting the conversion of testosterone into DHT. One study of 3040 men found that a daily dose of Finasteride led to a small increase in testosterone compared to men who did not take Finasteride, with the greatest increases occurring in men who had lower baseline testosterone levels at the start of the study(3). Muscle mass was not measured.

In another study, scientists compared testosterone replacement therapy in older men with and without Finasteride. The addition of Finasteride decreased serum DHT levels by approximately 50% but did not affect gains in physical performance or result in alterations in body composition when compared with testosterone alone(4).

Both the studies administered a daily dose of 5mg Finasteride, it is reasonable to consider that the 1mg daily dose for hair loss would result in less significant changes.

Can Finasteride use lead to muscle loss?

Most clinical studies on Finasteride have focused on its effectiveness for hair loss and prostate issues, with side effects typically being limited to sexual dysfunction, such as decreased libido and erectile dysfunction(5). Muscle loss has not been a prominent or consistently reported side effect in these studies.

Some users may notice a more pronounced reduction in muscle mass anecdotally. However, as Finasteride therapy only results in a modest increase or decrease in total serum testosterone, the variation can be attributed to other factors.

Other factors influencing muscle mass include individual differences in hormone metabolism, genetics, and overall health and fitness levels. Furthermore, the overall effect of Finasteride on muscle mass can be influenced by an individual’s exercise routine and dietary habits. Users taking the lower 1mg dose are highly unlikely to experience a loss in muscle mass.

References

1. Anitha B, Inamadar AC, Ragunatha S. Finasteride-Its Impact on Sexual Function and Prostate Cancer. J Cutan Aesthetic Surg. 2009;2(1):12-16.
2. Nassar GN, Leslie SW. Physiology, Testosterone. In: StatPearls. StatPearls Publishing; 2024. Accessed August 24, 2024.
3. Roehrborn CG, Lee M, Meehan A, Waldstreicher J. Effects of finasteride on serum testosterone and body mass index in men with benign prostatic hyperplasia. Urology. 2003;62(5):894-899.
4. Page ST, Amory JK, Bowman FD, et al. Exogenous Testosterone (T) Alone or with Finasteride Increases Physical Performance, Grip Strength, and Lean Body Mass in Older Men with Low Serum T. J Clin Endocrinol Metab. 2005;90(3):1502-1510.
5. Men on finasteride asked to stay vigilant for possible psychiatric and sexual side effects. GOV.UK. Accessed August 24, 2024.