This is a summary of a recent study by Patrick McQueen and colleagues, which suggested that finasteride is associated with reduced cholesterol in humans and slower progression of atherosclerosis in mice.

What is finasteride?

Finasteride is a drug called a 5α-reductase inhibitor and is commonly used in gender affirming healthcare as an antiandrogen. In people with testes, the enzyme 5α-reductase usually converts testosterone into its more potent form, dihydrotestosterone (DHT), which acts on the bodily tissues to produce masculinising changes. Finasteride inhibits 5α-reductase, and so blocks the production of DHT. By blocking the production of DHT, finasteride prevents masculinising effects.

Finasteride is usually used by trans women and transfeminine people as part of their feminising hormone treatment. It is also used to treat other conditions, including benign prostatic hypertrophy (enlargement of the prostate) and androgenetic alopecia (hair loss due to the effect of DHT on hair follicles).

What did the study examine?

The study sought to examine the effect of finasteride on cardiovascular disease. In particular, it looked at two markers which are risk factors for cardiovascular disease:

1. Atherosclerosis (hardening of the arteries due to cholesterol building up in the walls);
2. Plasma cholesterol (the level of cholesterol in the blood).

To examine these, the study had two steps:

1. Laboratory experiments on mice examined the association between finasteride administration and the rate of atherosclerosis.
2. Observations of humans who took part in the National Health and Nutrition Examination Survey between 2009 and 2016 examined the association between finasteride administration and plasma cholesterol.

What did the study find?

The first step of the study found that higher finasteride doses were associated with slower rates of atherosclerosis, lower plasma cholesterol levels, and lower levels liver inflammation in mice.

The second step of the study found that humans (specifically cis men in this study) who took finasteride had significantly lower plasma cholesterol levels than people who did not take finasteride.

The conclusion is that finasteride is associated with reductions in plasma cholesterol levels and slower rates of atherosclerosis progression. This potentially shows that finasteride could decrease the risk of cardiovascular disease.

Are there limitations to the study?

While the results of the study are promising, it is important to consider some limitations.

First, it is unclear how generalisable the results are to the trans population. In the second step of the study, the participants were cis men who were taking finasteride for benign prostatic hypertrophy or androgenetic alopecia. These results may not be straightforwardly projectable to trans women who are taking finasteride as part of feminising hormone treatment.

Second, the sample sizes in the second step of the study may be too small to support robust inferences. Out of 4800 survey respondents, only 155 people reported using finasteride.

Despite these limitations, the study provides promising preliminary evidence that finasteride could decrease the risk of cardiovascular disease by reducing plasma cholesterol.

Reference

McQueen, P., Molina, D., Pinos, I., Krug, S., Taylor, A. J., LaFrano, M. R., Kane, M. A., and Amengual, J. (2024). "Finasteride Delays Atherosclerosis Progression in Mice and is Associated with a Reduction in Plasma Cholesterol in Men". Journal of Lipid Research, 65 (3): 100507. https://doi.org/10.1016/j.jlr.2024.100507