Does Finasteride cause or prevent cancer?

A man about to swallow a finasteride pill with water
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The proof is in the science.

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Finasteride is a drug used to treat an enlarged prostate, and is also used at a lower dose to treat male pattern baldness. There have been multiple studies and conflicting research, looking into the link between finasteride and prostate cancer. But does finasteride prevent cancer?


What is finasteride and how does it work?

Finasteride has been traditionally used to treat an enlarged prostate. The prostate is a gland that is only present in the male anatomy. It produces the white fluid which carries the sperm when ejaculating. As men get older, the prostate grows in size, which is part of the natural ageing process. An enlarged prostate can increase the pressure placed on the bladder, which can cause symptoms such as the need to pass urine on frequent basis, difficulty urinating and difficulty emptying the bladder. Testosterone, a male hormone, is converted to Dihydrotestosterone (DHT) within the prostate, causing it to grow in size. This reaction happens only in the presence of an enzyme known as 5-alpha reductase. If you block 5-alpha reductase, then testosterone does not convert to DHT, and the prostate does not increase in size; and this is what finasteride does. It is known as a 5-alpha reductase inhibitor, which means it blocks the action of 5-alpha reductase, so that testosterone does not convert to DHT, which means that the prostate will not grow.


So, why is finasteride used to treat male pattern baldness?

Men that were prescribed finasteride to shrink their prostate, found that their hair was coming back. DHT not only enlarges the prostate, but also shrinks hair follicles on the head, to a point where they are no longer able to produce hair. Finasteride blocks the conversion of testosterone to DHT, which causes hair follicles to regenerate in the absence of DHT. The dose of finasteride required to shrink the prostate is 5mg, and the dose required to treat male pattern baldness is 1mg.


What is the link between finasteride and cancer?

One of the biggest pharmaceutical trials in history, looked at the link between finasteride and prostate cancer. It is known as the “Prostate Cancer Prevention Trial” (PCPT). It involved 18,882 men, and the aim was to find out whether finasteride could lower the chances of developing prostate cancer. The results from this study show that those who take finasteride on a daily basis, have a 25% less chance of developing prostate cancer. 56 men who were taking the placebo died from prostate cancer, and 42 men taking finasteride died from the same disease. This shows that there were less men who died from prostate cancer in those that took finasteride. However, some critics say that the figures are not statistically strong enough to make the claim that finasteride reduces the risk of prostate cancer.

This is a true statement, but the real value of the study lies in eradicating previous concerns about finasteride that were found in an earlier analysis of this study. A SWOG cancer research study reported that although the deaths relating to prostate cancer were 25% lower in those that took finasteride, there was an increase in cases with “high-grade” prostate cancer (a more aggressive form of the disease). According to the NHS, 15% of men with prostate cancer have normal PSA results (PSA tests measure the amount of prostate specific androgen in your blood and an elevated amount could be due to prostate cancer). Researchers have argued that finasteride improves the discovery of cancer in biopsies and screens, including the detection of high-grade cancer. They claim that the incidents of high-grade cancer were slightly higher in those taking finasteride because it made it easier to find.


The verdict: Does finasteride prevent cancer?

According to researchers, finasteride reduces the risk of prostate cancer. If you wish to start taking finasteride, you should discuss this with your doctor or pharmacist. All men should go for regular prostate examinations, especially those over the age of 55, black men and those with a family history of prostate cancer. If you are experiencing anything unusual, you should visit your GP as soon as possible.

Whilst all of our content is written and reviewed by healthcare professionals, it is not intended to be substituted for or used as medical advice. If you have any questions or concerns about your health, please speak to your doctor.