Viagra (sildenafil) was discovered somewhat by accident in the late 1980s when researchers were looking for a way to treat angina. The drug did well in opening up blood vessels, but one of the side effects was that men would get erections. The researchers then directed their studies toward how the drug opened up blood vessels in the penis (per Cosmos).
Up to 30 million men in the United States experience erectile dysfunction, according to the National Institutes of Health. Although there is no simple cure for erectile dysfunction, Viagra can help treat this condition.
Like many drugs, Viagra has side effects such as headaches, nasal congestion, low blood pressure, or upset stomach. Men over 50 who take Viagra are also at a higher risk for non-arteritic anterior ischemic optic neuropathy (NAION), which is a rare condition where blood flow is limited to your optic nerve. This is a type of eye stroke where you lose your vision. If you’re taking Viagra and experience a loss of vision in one or both eyes, see a doctor immediately. Aside from being older, other risk factors could lead to NAION.
Risk factors for this Viagra side effect
Medical researchers aren’t sure what causes NAION, but people with cardiovascular disease are more likely to develop this condition, according to Penn Medicine. You’re also at a higher risk if you have type 2 diabetes, high cholesterol, or obstructive sleep apnea. The optic nerve could lose blood flow if your blood pressure falls while you sleep. Often NAION will come without warning, with people waking up with vision loss in one eye. NAION might also obscure your vision, where a shadow, loss of contrast, or light sensitivity could occur.
Viagra belongs to a class of phosphodiesterase type 5 (PDE5) inhibitors that also include tadalafil, vardenafil, and avanafil. While these drugs increase blood flow to certain areas of the body, the optic nerve could see decreased blood flow. According to a 2022 study in Cureus, people taking Viagra could experience NAION as soon as an hour after taking the drug. Case studies show that NAION occurred in men over 50 who took Viagra, but one man who took udenafil (a PDE5 drug used in Korea) also experienced NAION. However, drugs to treat erectile dysfunction aren’t the only medications that are linked to NAION.
Other drugs besides Viagra that cause this side effect
NAION occurs in 2 to 10 out of every 100,000 people, making it the second leading cause of blindness from optic nerve damage, next to glaucoma. That’s about 0.01%.
Other drugs could also increase your risk of this condition. People with obesity and type 2 diabetes are prescribed semaglutide, which is the main ingredient in Ozempic and Wegovy. According to a 2024 study in JAMA Ophthalmology, NAION could be linked to semaglutide. The study compared more than 16,000 people who took either semaglutide or a different medication to treat obesity or type 2 diabetes. Among people with type 2 diabetes who took semaglutide, 8.9% of them would experience NAION within three years. Those who took semaglutide were four times more likely to develop NAION compared to the other diabetes medications. NAION developed in 6.7% of people taking semaglutide for obesity. People who took semaglutide to manage their obesity were 7.5 times more likely to develop NAION than if they took other weight-loss medications.