Propecia is a once-a-day pill treatment for male-pattern hair loss, or androgenetic alopecia. Male-pattern hair loss is when the hairline recedes and hair thins at the temples and crown. This condition is hereditary and affects close to 50 percent of the male population aged 50 years or older. It is sometimes recognized by a horseshoe-shaped fringe around the sides and the back of the head.
Propecia’s effects on hair loss were actually discovered by accident. Originally marketed as Proscar, doctors first prescribed 5 mg of finasteride (the active ingredient in Propecia) to treat benign prostatic hyperplasia (BPH), more commonly known as an enlarged prostate gland.
Merck later stumbled upon a remarkable side effect of Proscar treatment: some balding patients started to grow hair back. By dropping the dose of finasteride to 1 mg, researchers found a way to correct male-pattern hair loss.
In 1997, Merck introduced Propecia as a new use for finasteride. The company had developed the synthetic compound five years earlier.
With nearly half a billion dollars of research behind it, Propecia entered the drug market to high acclaim. After its first year, about 400,000 men in the U.S. were filling prescriptions for Propecia and taking the drug daily. Merck provided early Propecia users with a list of sexual side effects researchers had uncovered in clinical trials. However, it later came to light that the company wasn’t telling the whole story.
Upon approval of the drug, Merck disclosed that 3.8 percent of Propecia patients had one or more adverse sexual experiences, compared with 2.1 percent of patients taking a placebo. The company failed to warn, however, that these problems can persist even after patients stop taking the drug. In fact, Merck originally claimed that all of these issues would resolve after discontinuation of the drug.
The U.S. Food and Drug Administration (FDA) has since required updates to the drug’s label to reflect the potential for persistent sexual side effects with Propecia use. Thousands of men have sued Merck over allegations that the drug maker failed to provide adequate warnings and even “knowingly and recklessly omitted and concealed” known risks.
How Propecia Works
Baldness is caused by a potent male hormone called dihydrotestosterone, or DHT, which is produced in the adrenal glands, hair follicles, testicles and prostate gland. DHT is derived from the male sex hormone, testosterone. The enzyme 5α -reductase converts testosterone to DHT.
In people genetically predisposed to male-pattern baldness (androgenic alopecia), DHT binds to receptors in hair follicles at the top of the scalp. When the DHT hormone acts on these follicles, they shrink and gradually lose the ability to grow thick and healthy hair. As a result, the person’s hairline thins and recedes. Hair follicles on the back and side of the head are genetically resistant to DHT, which explains the common pattern seen in male baldness.
Propecia blocks the enzyme that converts testosterone to DHT, causing a rapid decline in DHT concentration.
Nearly 35 million men in the U.S. suffer from this type of hair loss. Other DHT-induced conditions include enlarged prostate and prostate cancer.
Propecia belongs to a class of drugs called 5-alpha-reductase inhibitors, which are used to treat conditions stimulated by DHT. Finasteride, the active ingredient in Propecia, blocks the enzyme that converts testosterone to DHT and causes a rapid decline in DHT concentration.
Propecia comes in the form of a tan, octagonal, film-coated tablet with a “P” logo on one side and “PROPECIA” embossed on the other. The drug’s label instructs users to take one 1 mg tablet once daily. Men can take Propecia with or without meals.
Within 24 hours of taking Propecia, the concentration of DHT drops by 65 percent. The full effects of daily Propecia use can take three months or more to appear. Stopping treatment leads to reversal of effect within 12 months, according to the drug’s label.
Propecia Side Effects
The most frequently reported adverse reactions to Propecia affect men’s sexual health. Although no clear causal links between Propecia use and sexual side effects have been established, finasteride suppresses the body’s level of DHT, which plays a major role in sexuality and sexual development, making the connection highly plausible.
An FDA analysis of adverse event data revealed a wide range of sexual side effects in otherwise healthy Propecia users ages 21 to 46. These problems persisted for an average of 40 months after the men ceased treatment.
The most common side effects associated with Propecia include:
- Decreased libido
- Erectile dysfunction
- Ejaculation disorder
Adverse sexual events are most notable in younger men. Several side effects have been found to improve or completely resolve once Propecia treatment is stopped, while others may continue to affect the patient for several months or even years. In some cases, sexual function never returns to normal.
Other side effects of Propecia include allergic reactions, including rash, itching, hives and swelling of the lips and face; breast enlargement and tenderness; depression; testicular pain; male infertility or poor quality of semen; and male breast cancer.
FDA Propecia Warnings
When evidence conflicted with Merck’s original assertion that the sexual side effects of Propecia would stop once treatment ends, the FDA revised the drug’s safety label accordingly.
The FDA reviewed 421 post-marketing reports of sexual side effects sent to its Adverse Events Reporting Systems (AERS) database from 1998 to 2011. A total of 59 cases in the AERS database reported sexual dysfunction that continued for at least three months after Propecia use ended.
In 2011, the FDA updated the drug’s label to include information about incidences of male breast cancer and a warning that erectile dysfunction may continue after the drug is no longer being used.
On April 11, 2012, the FDA made another revision, explaining that some patients continued to experience libido disorders, ejaculation disorders and orgasm disorders after they stopped taking the drug. The agency also added a description of reports of male infertility and/or poor semen quality that improved or returned to normal after drug discontinuation.
Women, Children & Pregnancy
Pregnant women should not handle crushed or broken Propecia tablets because of possible risk to male fetuses.
The FDA warns that Propecia is not approved for use in women and children. Women should not handle crushed or broken Propecia tablets when they are pregnant or may potentially be pregnant because of potential risk to a male fetus.
DHT is a hormone necessary for normal development of male genitalia. As a result, if a pregnant woman receives finasteride, the drug may cause abnormalities of the external genitalia of a male fetus, according to the FDA.
In female rats, low doses of finasteride administered during pregnancy have produced abnormalities of the external genitalia in male offspring, including decreased prostatic and seminal vesicular weights, delayed preputial separation and transient nipple development.
The drug also carries a warning that men 55 and older who take Propecia may have an increased risk of an aggressive type of prostate cancer. The warning is based on the dose to treat enlarged prostate, which is five times higher than the dose used for hair loss.
In June 2011, the FDA released a safety announcement warning that Propecia and other 5-alpha-reductase inhibitors may increase the risk for high-grade prostate cancer, the deadliest form of prostate cancer.
High-grade prostate cancer is highly aggressive and grows rapidly, often spreading to other areas like the lymph nodes and bones. Further, high-grade prostate cancer cells are large, difficult to treat and reappear more frequently than low- and intermediate-grade prostate cancers.
Although the cancer risk appears to be low, the FDA distributed the announcement to inform doctors and patients of safety revisions to the warning and precaution labels for this class of drugs. Evidence of the increased risk comes from two large clinical trials: the seven-year Prostate Cancer Prevention Trial (PCPT) and the four-year Reduction by Dutasteride of Prostate Cancer Events (REDUCE) trial.
Both trials sought to determine if finasteride could be used to lower the risk of prostate cancer. While PCPT and REDUCE did in fact result in decreased incidences of lower-risk forms of prostate cancer, patients in both trials were found to be at a greater risk for high-grade prostate cancer.
Emily Miller is an award-winning journalist who has held writing and editorial positions with numerous print and online publications around the U.S. She draws on her background as both a patient and a journalist to help readers understand complex health topics. Her most recent experience is in writing about litigation involving medicines that cause life-altering side effects.
- Grady, D. (2017, February 2).Trump Takes the Hair-Growth Drug Propecia. How Does It Work? Retrieved from https://www.nytimes.com/2017/02/02/health/donald-trump-hair-growth-drug-propecia.html?_r=0
- FDA.gov. (2014, January). Highlights of Prescribing Information. Retrieved from https://www.accessdata.fda.gov/drugsatfda_docs/label/2014/020788s024lbl.pdf
- National Institutes of Health. (2013, January 17). Androgenetic Alopecia. Retrieved from http://ghr.nlm.nih.gov/condition/androgenetic-alopecia
- U.S. Food and Drug Administration. (2012, April 11). Questions and Answers: Finasteride Label Changes.
- NY Daily News. (2012, April 16). Propecia and Proscar May Have More Sexual Side Effects than Labels are Telling. Retrieved from http://www.nydailynews.com/life-style/health/propecia-proscar-sexual-side-effects-labels-telling-article-1.1062408
- Merck & Co., Inc. (2012, April). Propecia Highlights of Prescribing Information. Retrieved from http://www.accessdata.fda.gov/drugsatfda_docs/label/2012/020788s020s021s023lbl.pdf
- Traish, A. et al. (2010, December 22). Adverse Side Effects of 5-alpha-Reductase Inhibitors Therapy: Persistent Diminished Libido and Erectile Dysfunction and Depression in a Subset of Patients. Retrieved from http://onlinelibrary.wiley.com/doi/10.1111/j.1743-6109.2010.02157.x/pdf
- Institute for Safe Medication Practices. (2013, January 9). Finasteride (Propecia, Proscar) and Possibly Persistent Sexual Side Effects Methylphenidate Pate (Daytrana) and Product Problems Update on Anticoagulants Dabigatran (Pradaxa) and Rivaroxaban (Xarelto). Retrieved from http://www.ismp.org/QuarterWatch/pdfs/2012Q2.pdf
- Hair Loss Learning Center. (n.d.). Propecia – Hair Loss Medication. Retrieved from http://www.hairlosslearningcenter.org/causes-of-hair-loss/propecia-hair-loss-medication.asp