Finasteride - treating hair loss by blocking the production of DHT


Finasteride is one of two currently FDA-approved medicines for the treatment of androgenic alopecia (male pattern hair loss). Developed on the back of insights around male sexual development, it was released in 1997 after over 20 years of development. It works by blocking the production of a hormone which degrades your hair follicles and that, in large-scale studies, has been shown to help maintain (and in some cases, promote) hair growth. However, as with all powerful medical treatments, it should only be taken under medical supervision and after carefully considering the risk of side effects.

A discovery born of a unique genetic condition

The development of finasteride can be traced back to a remote part of the Dominican Republic. In the 1970’s a young researcher Julianne Imperato-McGinley1 MD, traveled there in the early 1970s, following reports of young girls that literally changed into boys at puberty. In a seminal 1974 paper2 she described for the first time an extremely rare condition in which deficiency of an enzyme called 5-alpha-reductase causes genetically male babies to be born with no external genitalia. Instead, male characteristics literally sprout at puberty, causing the locals to dub the condition “Guevedoces”, which effectively translates as “penis at twelve”.

This research was noted by the head of basic research at Merck, Dr. P. Roy Vagelos, who was interested in the prostate-shrinking effects of the condition. He would lead an effort that would first result in the release of finasteride for prostate enlargement (1992) and for the treatment of male pattern hair-loss (1997).

Finasteride works by blocking the production of DHT

Dihydrotestosterone (commonly referred to as DHT), a derivative of testosterone, is responsible for the development of many male characteristics around puberty. However, in a classic example of a double-edged sword, it also plays a key role in male pattern hair loss later in life. Finasteride works by inhibiting the two of the three different forms of 5α-reductase which convert testosterone into DHT in your body. By reducing the production of DHT by as much as 71%3, it hinders its damaging effect on your hair follicles4.

In three studies5 involving 1,848 men from the ages of 18-41 with mild to moderate hair loss, it was found that after 12 months, 58% of men given a placebo had experienced further significant hair loss compared with 17% taking finasteride. After 2 years, 72% of the placebo group demonstrated hair loss compared with 17% of the men treated with finasteride. This increased to 100% of the men in the placebo group vs 35% of the men under treatment experiencing hair loss by year 5.

The benefit was not strictly limited to maintenance, in men with vertex baldness (hair-loss predominately on the top or crown of the head) growth in new hairs was seen in 48% of men being treated with finasteride at 12 months, rising to 66% of men by 24 months. However, this effect diminishes over time as in the same group of men new hair growth was only evident in 48% at the 5-year mark.

Benefits and risks from its use

As the clinical studies demonstrate, finasteride helps maintain hair growth in men experiencing male pattern hair loss over an extended period, and in a lucky few it promotes new hair growth over a couple of years. This maintenance effect typically kicks in after 6 months of continuous use and lasts only as long as the user continues to take the treatment. In studies, the effects of finasteride reverse over a period of 12-24 months after a patient stops taking it and their hair reverts to a similar state as those in the placebo group.

The key concern with using finasteride is around the circa 3% compared to of men who experience sexual dysfunction while taking the drug. They can experience erectile and libido problems which, in studies, abate after months of ceasing to take finasteride. Anecdotally, there are reports that these sexual problems can last considerably longer6 and some men experience depression, which is an area under further study.

A powerful tool to be used under the right conditions

Finasteride is a powerful tool in the fight against hair loss, which works by blocking the production of DHT before it can damage your hair follicles. However, as it is a serious pharmaceutical, it must be used under the guidance of a medical professional and after careful consideration of the potential side effects. In combination with minoxidil, it can provide a powerful one-two punch to your hair loss and help keep your hair fit and healthy. At Hair Fitness, we are developing affordable and effective treatment programs incorporating finasteride to help you get on top of your hair.

  1. Dr Imperato-McGinley went on to become, amongst many other things, a Director at Cornell, after 25 years of ground breaking research. You can read more about her, frankly amazing, career here.
  2. Steroid 5alpha-reductase deficiency in man: an inherited form of male pseudohermaphroditism. Science 1974.
  3. McConnell JD, Wilson JD, George FW, Geller J, Pappas F, Stoner E (March 1992). “Finasteride, an inhibitor of 5 alpha-reductase, suppresses prostatic dihydrotestosterone in men with benign prostatic hyperplasia”. J. Clin. Endocrinol. Metab. 74 (3): 505–8.
  4. For a full discussion of the role of DHT in male pattern hair-loss and it’s interplay with genetics please see our blog post here.
  5. see for full details of the FDA’s licencing of finasteride.
  6. Michael S. Irwig MD , Swapna Kolukula MB BS. Persistent Sexual Side Effects of Finasteride for Male Pattern Hair Loss, Journal of Sexual MedicineVolume 8 Issue 6 June 2011.

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