Propecia first came on the market in 1997 and became hugely popular right away as manufacturer Merck heavily promoted it to treat hair loss in men. The company originally developed the drug, known generically as finasteride to treat enlarged prostates, but discovered that hair growth was a side effect during clinical trials.

The company then tested a lower dose of the drug in clinical trials for hair loss and found it to be effective at treating male pattern baldness. Now, after making millions on the drug, Merck is facing tough criticism and even some lawsuits over the side effects of using Propecia. These are severe in some men and may include persistent sexual dysfunction and cancer.

Finasteride, Prostate Enlargement, and Hair Growth

Finasteride was first developed by Merck as the brand name Proscar and was approved by the U.S. Food and Drug Administration (FDA) in 1992 to treat a condition called benign prostatic hyperplasia, or an enlarged prostate gland. It was found to be effective for this condition, but during clinical trials the researchers found a side effect that could be leveraged for another brand name product.

Merck developed finasteride to inhibit a particular enzyme called 5-alpha reductase. This is an enzyme that transforms the hormone testosterone into dihydrotestosterone. It is this transformation that can lead to an enlarged prostate, prostate cancer, and hair loss. Proscar inhibits that enzyme in order to treat an enlarged prostate.

During clinical trials for Proscar, researchers saw that participants experienced hair growth as a side effect. Merck realized it could have a blockbuster drug if it could prove that finasteride at the right dose treated male pattern baldness effectively. The reduced the dose from five milligrams for prostate treatment to one milligram and found it to be effective. They called it Propecia and got it approved by the FDA in 1997.

Common Propecia Side Effects

The story of Propecia’s origins is one of the rare instances in which a side effect of a drug turns out to be positive. Most side effects are considered negative, and at best mild and not too disruptive. Although Propecia came from a side effect, while used as a treatment for male pattern baldness, it can result in certain side effects that are not as welcome as re-growing hair.

Unfortunately for the men taking Propecia—it is not indicated for use in women—the most common side effects are related to sexual dysfunction. Ejaculation disorder, erectile dysfunction, and a decreased libido are among the most commonly reported side effects. Other potential Propecia side effects are testicle pain, changes in breast tissue, and depression. An allergic reaction is also possible and may be severe.

Severe Sexual Dysfunction

Of all the side effects that Propecia is known to cause, sexual dysfunction is the most commonly problematic and also controversial. The controversy is not that these side effects are possible. That was known early on and the label does indicate that these are potential side effects. The problem is that Merck failed to warn patients that sexual dysfunction could persist long after a man stops using the drug. This is considered severe to those patients who have experienced it and had their lives changed for months, and even for years after using Propecia.

The FDA issued a warning about persistent sexual dysfunction in 2012 when it stated that both Propecia and Proscar would need to include additional label warnings. The new warnings needed to include that the known sexual dysfunctions could possibly persist after discontinuing use of the drugs.

The announcement came from the FDA following a barrage of adverse events reported to its reporting system. From analyzing the information the FDA found that more than 400 reports indicated that the sexual dysfunction side effects occurred and in more than half of cases lasted for up to three months after use of the drug was discontinued by patients. There were also reports of low sperm quality, raising questions about how Propecia might affect fertility.

Breast and Prostate Cancer

The persistent sexual dysfunction that some men experienced with Propecia was very damaging to their health, mental health, relationships, and self-esteem. This side effect is not the only one, though, that caused serious damage to the lives of some men using the hair-growth medication. In 2011 the FDA announced that finasteride could be linked to some cases of prostate cancer and evidence has also linked it to breast cancer.

Counterintuitively, finasteride actually reduces the risk of most types of prostate cancer, but has been found to increase the risk of a certain type of aggressive cancer: high-grade prostate cancer. The risk is considered to be low, but the type of cancer is serious and life-threatening. It grows quickly and readily spreads to other parts of the body, making it difficult to treat.

Although the FDA has not issued a specific warning about it, there is also some evidence that breast cancer can be a side effect of Propecia. It was already known that finasteride can cause changes to breast tissue as a side effect. Now a study has shown that the risk of developing breast cancer is slightly elevated in men taking finasteride as compared to the general population. Any change in breast tissue is to be taken seriously even though the general risk of developing this kind of cancer is low.

If you used Propecia and suffered any of the debilitating side effects, you may want to join the other men who are suing Merck and accusing the company of not doing its job in warning patients. Most men involved in these cases feel that the company never warned them that sexual side effects would last, in some cases for months, after stopping use of the drug.

Many state they would have reconsidered using it if they had known the risk. Some researchers reviewed Merck’s clinical trials and agreed that the company did not adequately test Propecia and therefore did not do all it could to warn patients of the potential risks. Speak with a lawyer to find out what your rights are and if you have a strong case against Merck.