by Jonathan Greengrass

Created on: July 24, 2011   Last Updated: July 25, 2011

Propecia, also known by it's generic name Finasteride, is a synthetic anti-androgen used to treat Male Pattern Baldness (MPB). In higher doses, Finasteride is also used to treat benign prostatic hyperplasia, and at this dosage the compound is marketed by its producer Merck as Proscar. Finasteride works by inhibiting the enzyme type II 5-alpha reductase, which converts free flowing testosterone into DHT.

The drug is one of only two FDA approved treatments for MPB, the most common form of male hair loss, and is used by millions of men worldwide. It is considered a low side effect drug in terms of the prevalence of the most common side effects. However, there are some side effects common enough that users should be aware of them before choosing to take the drug. The vast majority of symptoms are sexual in nature, and are listed and explained below.

The most common side effect of Propecia is abnormal ejaculation. This occurs in roughly 7.2% of men according to Merck's product information. However, like most of the side effects of the drug, the effects seem to be temporary and stop either when the drug's use is discontinued or after a reasonable amount of time taking the drug. The next most common effect is decreased ejaculatory volume, which is found in roughly two out of every hundred men taking the drug. Similar to the previous side effect, this is listed as a temporary side effect and after discontinuation of the drug normal ejaculatory volume returns. Other sexual side effects of the drug include testicular pain, abnormal sexual function (2.5 %), impotence (1.1%), erectile dysfunction (1.3%) and ejaculation disorder (1.2%). 

In addition to the above sexual side effects, the use of Propecia has been known to cause gynecomastia. Gynecomastia refers to the development of large mammary glands in males, resulting in the enlargement of the breast. This side effect is known to occur in around 2.2% of men who use the drug. Most users find this to be temporary and even with continued use of the drug the effects eventually dissipate. However it is worth stating that for others the symptoms occur until use of the drug is stopped. The use of the drug has also been linked to an increased incidence of male breast cancer. The UK's Medicines and Healthcare products Regulation Agency concluded that whilst the incidence of the disease within Propecia users was not significantly larger than within the general population, it is still necessary to list this risk in the product information.

Finally, Propecia should not be handled by pregnant women or women who aim to become pregnant, as it is known to cause birth defects in children. It is thought to be safe for women to handle whole tablets, provided they are not broken or crushed. Ingestion of Propecia is not safe for females and could lead to severe birth defects in children. Crushed tablets should not be handled as the drug can be absorbed through the skin.

As a closing point, it is worth noticing that Propecia is subject to an incredible amount of internet hysteria regarding the prevalence of the side effects. It is likely that many users are taking their own experience as representative of the whole community, and thus the 1-2% of users who experience sexual side effects are concluding that this is the experience of the whole population. Hair restoration specialists who apply the drug on a day to day basis do not report a prevalence of side effects that is significantly greater than Merck's stated risks, and so far no major drug advisory board has asserted that Merck have under-reported the risks of side effects. If you are considering taking this drug, be selective with the sources you use to make your decision. 

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