Dear Dr. Roach: I am 47 years old and 6 feet tall. I weight 185 pounds, exercise regularly, and am in overall very good health. I take 5 mg of Crestor and a multivitamin daily.

I recently took a generic 12-hour, maximum-strength nasal decongestant to manage typical sinus pressure and congestion. Within an hour of taking the medication, I noticed a dull and consistent pain in both testicles, which lasted for much of the day. I also noticed a strain in starting and maintaining a stream while urinating.

I took this medication two days in a row with the same negative result. The following day, I passed on taking it, and the pain and straining disappeared. Any correlation between the decongestant and the pain I experienced?

— A.K.

Answer: Absolutely. This is a known complication from decongestants such as pseudoephedrine (Sudafed). Decongestants are in the class of medicines called “alpha agonists.” The goal of the decongestant is to reduce swelling in your nose and sinuses. They work by constricting tiny muscles in the blood vessels (a special type of muscle called “smooth muscle,” which is different from the muscles in your limbs or heart), decreasing blood flow to the area, and relieving congestion. They work pretty well.

The problem is that they don’t just constrict the blood vessels in your nose, they constrict blood vessels everywhere. For most people, this isn’t a problem; however, decongestants can raise the blood pressure high enough that even if it’s controlled on medicines, it can get uncontrolled. It can be dangerously high on rare occasions, so people with high blood pressure should ask their doctors about decongestant medications by mouth and ideally check their blood pressure while on these medicines.

However, there’s another place with smooth muscle, and that is a man’s prostate. The effect of an alpha agonist (an “agonist” stimulates a receptor, while a “blocker” obviously blocks it) is to constrict the smooth muscle in the prostate, which closes the urethra — the tube that carries urine outside of the bladder. This caused you to strain to urinate.

In older men, decongestants can prevent them from being able to urinate at all, and they’ll need an emergency visit for a catheter until the medicine wears off. The most common treatment for a symptomatic enlarged prostate is an alpha blocker, so it makes sense that an alpha agonist can worsen things.

Antihistamines, which you might think would be a good choice for nasal symptoms, can unfortunately affect the bladder through an entirely different receptor (the muscarinic nicotine receptor). This happens more with older antihistamines, like chlorpheniramine (Chlor-Trimeton) and diphenhydramine (Benadryl). They keep the bladder from being able to squeeze hard enough to overcome the resistance from an enlarged prostate.

So, men with prostate issues and nasal symptoms should use a new antihistamine like cetirizine (Zyrtec) or fexofenadine (Allegra), which don’t usually cause problems. They can also try a topical decongestant spray like Afrin, but never for more than three days. The body gets used to taking it, and people get terrible symptoms if they stop.

Contact Dr. Roach at ToYourGoodHealth@med.cornell.edu.