If you're taking Propecia, weight lifting and hoping to bulk up your guns, there's a chance you may have heard word around the schoolyard that the drug can have an effect on your muscle mass. But is there any truth to these whispers?
The reality of the situation is that hard data on the subject is still quite limited. Effects on muscle mass are certainly not among the drug's most well documented side effects, nor are they too widely reported.
But some organizations are just beginning to convey reports from men who claim to have experienced muscle-related changes as part of their Propecia experience. Whether or not there's enough evidence to raise alarm bells is ultimately up to you, but knowing the drugs you take inside and out is never a bad idea.
A handful of small studies and self-reported claims illustrate that some men have experienced muscle-related issues as a result of taking Propecia (finasteride).
What Is Propecia?
Before we can understand why "Propecia" and "muscle mass" are even used in the same sentence, it's important to understand the basics of the drug. First off, "Propecia" (like "Proscar") is actually just a brand name for the generic finasteride, which the U.S. Food and Drug Administration officially approved as an oral treatment for male pattern hair loss (also known as androgenetic alopecia) in 1992. If "male pattern" wasn't a giveaway, this drug is intended for use by men only.
As a hair loss drug, finasteride is what's known as a 5-alpha reductase inhibitor. That's because it blocks the production of 5-alpha reductase, an enzyme that converts testosterone to dihydrotestosterone (DHT), a male hormone. In addition to being associated with prostate growth, DHT is also correlated with male pattern baldness. Finasteride's relationship with testosterone is a very likely culprit for why people are so curious about its potential effects on muscle mass.
Potential Side Effects of Finasteride
As the FDA notes, in three 12-month controlled clinical trials for Propecia, 1.4 percent of its patients discontinued use due to adverse experiences. Among these adverse experiences, nothing involving muscle mass was recorded by the FDA. The known side effects — and how the reports from genuine Propecia users compare to those taking placebos — include:
- Decreased libido: 1.8 percent reported with Propecia, 1.3 percent with placebo
- Erectile dysfunction: 1.3 percent reported with Propecia, 0.7 percent with placebo
- Decreased volume of ejaculate: 0.8 percent reported with Propecia, 0.4 percent with placebo
As you can see, the on-the-record side effects of finasteride typically have to do with sexual dysfunction (though larger doses of finasteride may also cause breast enlargement, breast tenderness or rash, and some hypersensitivity has been reported to the FDA since the drug has been on the market). According to Mayo Clinic, users also commonly experience chills, cold sweats, confusion and dizziness, among other minor discomforts.
Among the 945 men the FDA's report covers, these side effects usually resolved when the drug was discontinued. Like the FDA, Mayo does not report any known muscle-related side effects.
Does Finasteride Affect Muscle Growth?
If the national standard bearer for rigorous clinical trials didn't find a relationship between Propecia and muscle mass, why the talk of finasteride and bodybuilding gains? A small study published in the March 2016 edition of the journal _Andrology _may be what first raised those eyebrows. Although it still focuses largely on sexual side effects, it does contain some muscle-related reports.
Out of 79 participants with a mean age of 33.4 years and a mean finasteride usage history of 27.3 months, the Andrology study finds that 38 percent of respondents reported involuntary muscle spasms and more rigidity in physical movements. A loss of muscle tone or mass was the most commonly reported somatic side effect, reported by 51.9 percent of the men studied. However, 38 percent also reported increased body weight.
Following not too far behind in 2017, a Summary Safety Review released by the Canadian government's Health Canada assessed finasteride's potential effects on the risk of adverse muscle-related conditions such as muscle tissue breakdown (rhabdomyolysis) and muscle pain, weakness, stiffness or atrophy (muscle wasting). Health Canada notes that it has received 11 reports of serious muscle-related side effects linked to finasteride and has further assessed four of those cases.
World Health Organization Stats
The World Health Organization's VigiAccess database maintains a current count of side effects reported by international drug authorities in more than 110 different countries. As of their August 2019 figures, the counts for muscle-related side effects from finasteride users, based on a total of 15,870 records, are:
- Muscle atrophy: 169
- Muscular weakness: 112
- Muscle spasms: 98
- Muscle twitching: 56
- Musculoskeletal pain: 51
- Musculoskeletal stiffness: 39
- Musculoskeletal chest pain: 21
- Musculoskeletal discomfort: 16
- Muscle disorder: 25
- Muscle discomfort: 3
- Muscle tightness: 11
- Muscle fatigue: 5
- Muscle rigidity: 4
- Muscle hypertrophy: 2
In their 2017 assessment of WHO's reports, Health Canada noted that the reports did not contain enough information to explicitly identify finasteride as the culprit for these side effects. From 1993 to 2019, WHO reports that an average of 3.74 percent of all the finasteride users in their database experience any sort of side effects at all.
"...the risk of serious muscle-related side effects with the use of finasteride [can] not be ruled out." — Health Canada, 2017
Muscle Mass in Review
It's worth mentioning that the figures provided by Andrology, the World Health Organization and Health Canada are self-reported cases of men who have taken finasteride and claim to experience muscle-related issues, from spasms to a loss in muscle mass. The sources collected the data but, of course, did not administer physical muscle mass readings.
Other studies that delve into whether or not finasteride affects muscle growth have more to do with the drug's potential effects on male sexual performance. These studies focus on erectile dysfunction, assessing smooth muscle content present in erections after consistent finasteride use. In a wide-ranging review of studies published in the June 2014 edition of the Korean Journal of Urology, it's noted that finasteride commonly reduces penile smooth muscle relaxations and trabecular smooth muscle content in animal subjects such as rats.
Though these relatively new reports may be the start of much-needed further studies on finasteride's affect on muscle growth, Health Canada puts it most succinctly: "Health Canada's review of the available information concluded that the risk of serious muscle-related side effects with the use of finasteride could not be ruled out." In fact, the organization recommends that manufacturers in the country update the product information to educate users of this potential risk.
- U.S. Food and Drug Administration: "Propecia (Finasteride) Tablets for Oral Use, Initial U.S. Approval: 1992"
- U.S. Food and Drug Administration: "5-Alpha Reductase Inhibitor Information"
- National Cancer Institute: "NCI Dictionary of Cancer Terms: 5-Alpha Reductase Inhibitor"
- Mayo Clinic: Drugs and Supplements: "Finasteride (Oral Route)"
- Andrology: "An Observational Retrospective Evaluation of 79 Young Men With Long-Term Effects After Use of Finasteride Against Androgenetic Alopecia"
- Wiley Online Library: "An Observational Retrospective Evaluation of 79 Young Men With Long-Term Adverse Effects After Use of Finasteride Against Androgenetic Alopecia"
- Korean Journal of Urology: "The Dark Side of 5α-Reductase Inhibitors' Therapy: Sexual Dysfunction, High Gleason Grade Prostate Cancer and Depression"
- Government of Canada: Health Canada: "Summary Safety Review — Finasteride — Assessing the Potential Risk of Serious Muscle-Related Side Effects"
- World Health Organization: Collaborating Centre for International Drug Monitoring: VigiAccess: "Finasteride"