Taking Viagra Has An Unexpected Effect On Blood Pressure

The little blue pill called Viagra emerged from Pfizer's labs almost 30 years ago, and it still remains one of the most popular drugs to treat erectile dysfunction (ED). Viagra works by blocking an enzyme called PDE5. This helps relax blood vessels, improving blood flow to the penis.

Viagra wasn't originally intended to treat ED. Its active ingredient, sildenafil, was being studied to treat high blood pressure. However, when researchers noticed in clinical trials that Viagra came with erections as a side effect, it was repurposed as an ED drug. 

Given its history, it shouldn't be too much of a surprise to know that Viagra can cause a temporary drop in your blood pressure. However, if you have uncontrolled high blood pressure, taking Viagra won't reduce your blood pressure enough to improve your cardiovascular health. In a 2002 study in Urology, men with normal blood pressure and high blood pressure took 100 milligrams of sildenafil to see its effect on blood pressure compared to the men's baseline the night before. In both groups, sildenafil significantly lowered systolic blood pressure by 6 millimeters of mercury and diastolic blood pressure by 4.5 millimeters of mercury on average. Men age 49 and older saw even greater reductions in blood pressure, but not to the extent that they experienced hypotension. 

Although Viagra doesn't work well enough to be used to treat high blood pressure, you should still be cautious about taking it if you are using certain other medications that could interact with it.

Hypotension — when your blood pressure is too low — is one of the more serious side effects of Viagra. Hypotension could make you feel dizzy or lightheaded, but it could also cause a heart attack or stroke.

This side effect can occur if you're also taking nitrates for chest pain. You should also talk to your doctor before taking Viagra if you're taking high blood pressure medications. Viagra also shouldn't be used if you're taking drugs to treat heart failure such as riociguat (Adempas) or using street drugs called "poppers."

(Here's what could happen if you take Viagra without ED.)

Another drug that contains sildenafil — Revatio — treats pulmonary hypertension, which is a hereditary condition that restricts blood from your heart to your lungs. This is a lower dosage of sildenafil taken several times a day to relax the arteries around your lungs. If you're already taking Revatio (or other PDE5 inhibitors) for pulmonary hypertension, you should avoid Viagra.

Even if your blood pressure is normal, it's best to discuss your ED with your doctor before asking for a Viagra prescription. ED can be caused by psychological issues such as depression, stress, or relationship problems. You could also experience ED if you have problems sleeping, low testosterone, or substance use disorder. High blood pressure, type 2 diabetes, obesity, or high cholesterol could also be causing your ED, so it's important to address these to find the right treatment plan.

ED can be an early warning sign of cardiovascular problems later in life, according to a 2021 article in the Journal of Clinical Medicine. It's not that ED causes heart disease. The blood vessels around the penis are much smaller than the larger blood vessels near the heart, brain, and lungs. Therefore, these smaller blood vessels are more likely to show signs of damage. ED could precede a cardiovascular event such as a heart attack or stroke by three years. Your doctor should look at your risk factors for heart disease but also consider unconventional risk factors such as your family history of metabolic issues, alcohol use, and the severity of your ED during intercourse.