6 strange side effects of common prescription drugs

By Naveed Saleh, MD, MS, for MDLinx
Published November 28, 2018

Key Takeaways

Most physicians may not realize that the terms "side effect" and "adverse effect" mean different things. According to Dorland's Medical Dictionary, the term side effect refers to "a consequence other than the one(s) for which an agent or measure is used" and can be either beneficial or detrimental. Wakefulness, for instance, can be considered a positive side effect of caffeine. The terms adverse effect, adverse event, and adverse reaction, however, refer to negative side effects only.

In addition to being positive or negative, side effects can also be flat-out weird. As a physician, you may be intrigued by which drugs have unusual side effects, and this knowledge may come in handy when treating and advising your patients.

Here are some of the strange side effects of a few commonly prescribed drugs:

Rifampin and sweat

Rifampin is usually used in combination with other drugs to treat tuberculosis, but can also be used on its own to treat latent disease in patients who can't tolerate isoniazid. Rifampin is a derivative of rifamycin, a bactericidal agent used to treat Mycobacterium tuberculosis, and inhibits DNA-dependent RNA polymerase. Rifampin turns sweat, urine, and tears orange. Although harmless, orange tears can permanently stain contact lenses. On a related note, possible adverse effects of rifampin include skin rashes, thrombocytopenia, nephritis, and liver dysfunction.

Trazodone and priapism

Trazodone is an atypical antidepressant typically reserved for special uses. More specifically, trazodone is a serotonin modulator and boosts serotonin levels. Serotonin is a neurotransmitter that is key in maintaining cognitive homeostasis. This drug is commonly used before sleep when a sedating effect is desired—as in cases of insomnia. In addition to orthostatic hypotension, trazodone can also cause priapism, or persistent or painful erection.

Finasteride for hair growth

Did you know that finasteride is the generic name for both Proscar and Propecia? Finasteride (Proscar) is used both on its own and in combination with doxazosin for the treatment of benign prostatic hypertrophy. Finasteride (Propecia) is used to treat male-pattern baldness.

Finasteride is a 5-alpha reductase inhibitor that blocks the switch from testosterone to dihydrotestosterone. Testosterone is responsible for both prostate enlargement and hair loss.

Potentially, finasteride could be used to treat both hair loss and benign prostatic hypertrophy in the same patient, thus yielding a two-fer. Keep in mind, however, that undesirable adverse effects of finasteride include decreased libido, erectile dysfunction, and ejaculation issues.

Bimatoprost and eye color

Few physicians would expect that a drug could change eye color, but bimatoprost is a prostaglandin analog available as a 0.03% ophthalmic solution that can do just that. The mechanism of action of bimatoprost has yet to be elucidated. It is used to treat eyelash hypertrichosis, as well as glaucoma. When applied only to the skin of the eyelid, this drug doesn't change iris color to brown, but when applied directly to the eye for glaucoma, it does.

Capecitabine and fingerprints

Capecitabine is an oral 5-fluorouracil prodrug used to treat metastatic colorectal carcinoma and breast cancer. Intriguingly, after taking the drugs for as little as 2 weeks, a small number of patients first developed hand-foot-and-mouth disease and then lost their fingerprints altogether. These patients were often unaware that they lost their fingerprints until they encountered government officials, such as when traveling or getting a driver's license, or when performing fingerprint scans for computers or telephones. Notably, although fingerprint loss in some patients taking capecitabine reverses, many people who experience this strange side effect end up with permanent loss even after discontinuing the drug.

"The significance of capecitabine-induced adermatoglyphia [fingerprint loss] will continue to increase as fingerprint identification continues to advance not only in scanning technology but also in global utilization," wrote Philip R. Cohen, MD, Department of Dermatology, University of California, San Diego, CA, in an article published in Cureus. "Therefore, it is essential that patients receiving capecitabine are aware of this potential adverse cutaneous sequellae."

Levodopa and creativity

Some patients with Parkinson's disease who were administered levodopa have been reportedly gifted with newfound creativity. This creativity has led to book publication and vivid paintings.

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