Study Finds Links Finasteride to Penis Shrinkage in Rats

A new study reveals that finasteride is linked to penis shrinkage in rats. Finasteride is sold under the brand name Propecia (when prescribed in 1 mg doses for mail pattern baldness) and Proscar (when prescribed in 5 mg doses for enlarged prostate). Merck & Co manufactures Finasteride.

The study, to be published in the Journal of Sexual Medicine, states that male rats treated with oral finasteride for four weeks experienced a 25% reduction in the weight of their penis (corpora cavernosa), said the Examiner. In his comment, Dr. Michael Irwig, Assistant Professor of Medicine at the George Washington University School of Medicine said, “This is consistent with what many men have told me that they have had shrinkage in their penis after taking Propecia,” according to The Examiner. Dr. Irwig’s revolutionary study on Propecia’s permanent and severe side effects appeared in the Journal of Sexual Medicine last March.

The current study—“Effects of Oral Finasteride on Erectile Function in a Rat Model” by M.G. Zhang—concluded that “In a rat model, finasteride treatment for 4 weeks reduces the weight of the corpus cavernous (penis) but appears not to affect the erectile responses to electrical stimulation of the cavernous nerve. As erection is a complex process involving important signaling in the brain, further studies are necessary to demonstrate the long-term effects of finasteride on both central and peripheral neural pathways of erection.”

Meanwhile, the U.S. Food & Drug Administration just broadened its probe of Propecia’s safety, said The Examiner.

We also just wrote that Health Canada issued a warning about Proscar, Propecia, Avodart, and Jalyn medications, all prescribed for the treatment of enlarged prostate or mail-pattern baldness. The drugs may increase risks for a serious type of prostate cancer. Avodart and Jalyn, known generically as dutasteride, are prescribed to treat enlarged prostate, also known as benign prostatic hyperplasia.

Risk was seen in the 5-mg dose of finasteride, sold as Proscar. The 1-mg strength of the drug sold as Propecia was not included in the trials, but the potential risk was not ruled out, said Health Canada.

As we’ve written, Propecia is part of the drug class 5-alpha reductase inhibitors (5-ARIs), as are Merck’s Proscar and GlaxoSmithKline’s Avodart and Jalyn. According to the FDA, almost 5 million men were prescribed one of these drugs during 2002-2009, which work by preventing the androgen testosterone conversion to DHT, a hormone critical to male sexual performance.

We previously wrote that a Colorado man filed suit against the maker of Propecia, claiming the male baldness drug caused him to suffer erectile dysfunction and other sexual problems. The claim is just one of many Propecia lawsuits filed against Merck & Co. by men who say that the drug caused sexual issues.

Last March, a group of researchers at Boston University published a study that revealed that, in a small number of cases, erectile dysfunction linked to 5-ARIs may continue after the drugs have been discontinued. Other men taking the drugs reported reduced ejaculation and semen volume and depression. In some cases, men experienced problems after taking the drugs.

Such drugs may also increase the risk that users will develop male breast cancer as well as issues with sexual dysfunction and increased risks for high-grade prostate cancer.

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