When men take finasteride for hair loss, their attention is directed to the hair and scalp. When adverse events (AEs) occur in other systems and areas of the body, it might not be obvious that finasteride could be the culprit. But the drug alters levels of chemical messengers in the blood as well as peripheral tissue such as the reproductive system, liver and lungs.
More than two decades of AE data as well as accumulating research show 5-alpha reductase inhibitors can have adverse effects on multiple systems and functions. Most research focuses on sexual and neuropsychiatric events, while there are only a handful of papers investigating musculoskeletal effects.
Following is a summary of musculoskeletal AEs in men ages 18–40. Data was downloaded from FDA’s Federal Adverse Event Reporting System via the Public Dashboard. These filters were applied: Sex: Male / Age: 18–40 / Date Last Received: 2012–2021 / Suspected Product: finasteride only / Concomitant Products: none. Exclusion of other products reduces confounding factors.
AEs were disaggregated from cases, so the table does not indicate the composition of events within individuals.
| Category & adverse events | Total | Proportion |
| Weakness Asthenia – 74 Muscular Weakness – 25 Myopathy – 5 Pelvic Floor Muscle Weakness – 1 Muscle Fatigue – 1 | 107 | 31% |
| Atrophy Muscle Atrophy – 83 Rhabdomyolysis – 4 | 87 | 26% |
| Pain & inflammation Arthralgia – 40 Myalgia – 29 Musculoskeletal Pain – 3 Myositis – 1 Musculoskeletal Discomfort – 1 Muscle Discomfort – 1 | 75 | 22% |
| Spasms & tightness Muscle Twitching – 33 Muscle Spasms – 8 Muscle Tightness – 5 Myosclerosis – 4 Muscle Contractions Involuntary – 3 Musculoskeletal Stiffness – 1 | 54 | 16% |
| General & other Muscle Disorder – 15 Musculoskeletal Disorder – 1 Muscle Hypertrophy – 1 | 17 | 5% |
| Total musculoskeletal adverse events | 340 | 100% |
The 340 musculoskeletal AEs made up 3.9% of all AEs in cases meeting the search criteria.
See also: Research: effects of 5-alpha reductase inhibitors on musculoskeletal system
Comparison with minoxidil
Minoxidil is another hair loss treatment taken by a similar population as finasteride. Comparing musculoskeletal events of the two drugs can help disentangle drug effects from characteristics of a population.
Musculoskeletal events were extracted from minoxidil cases in FDA FAERS with the same filters applied: Dates: 2012–2021 / Sex: Male / Age: 18–40 / Suspected Product: minoxidil only / Concomitant Products: none.
Minoxidil had just 8 musculoskeletal AEs during the 10-year period.
| Finasteride | Minoxidil | |
| Musculoskeletal AEs | 340 | 8 |
| All AEs | 8,348 | 2,952 |
| % of all AEs | 4.1% | 0.3% |
The proportion of musculoskeletal AEs of finasteride was 13.7x greater than that of minoxidil. The ratio suggests finasteride may elevate the risk of musculoskeletal events among men ages 18–40, compared to another drug used by a similar population for the same condition.