Viagra (sildenafil): uses, side effects, interactions, and more

Viagra (sildenafil), often referred to as the “little blue pill,” is a brand-name prescription drug best known for treating erectile dysfunction or “ED”. 

ED occurs when you can’t get or maintain an erection for satisfying sex—and it’s very common, affecting 30 million men in the U.S. (Nunes, 2012). If you find that you’re one of those men and are having a difficult time getting or staying aroused, your healthcare provider may recommend Viagra to help you have harder and longer-lasting erections.  

Let’s learn a little bit more about this popular blue pill.

Viagra (generic name sildenafil citrate) is a prescription drug that helps treat erectile dysfunction (ED). It is one formulation of the drug sildenafil. (Sildenafil is also found in different formulations under the brand name Revatio.)   

Viagra belongs to a class of drugs called PDE5 inhibitors (phosphodiesterase-5 enzyme inhibitors). PDE5 inhibitors work by blocking an enzyme called PDE5, allowing for more blood to flow to your penis so that you can maintain your erection.  

It is important to note that Viagra can only help you get hard and stay hard if you are already aroused. You have to be sexually stimulated for Viagra to work. 

Viagra is approved by the U.S. Food and Drug Administration (FDA) for the treatment of erectile dysfunction (ED). It has been shown to help up to 65% of men with ED maintain their erections (McMahon, 2019).

The FDA also approves other formulations of sildenafil—the active ingredient in Viagra— for treating a condition known as pulmonary arterial hypertension, or high blood pressure, in your heart and lung arteries. 

Under some circumstances, a healthcare provider might prescribe sildenafil off-label to treat other conditions, including: 

• Raynaud’s phenomenon: A condition in which there’s poor blood flow in areas like the fingers and toes. In clinical trials, sildenafil was more effective in treating this condition than placebo, although the trials were very small (Corbin, 2004).

• Altitude sickness: Sildenafil may improve oxygen levels in people with altitude sickness (Perimenis, 2005).

• Female sexual interest/arousal disorder (FSAID): Biological females with FSAID have trouble getting aroused or experience low desire. In clinical trials, people with FSAID who took sildenafil had a higher number of satisfying sexual events compared to placebo (Tuiten, 2018). 

Viagra usually causes mild side effects or none at all. Some of the most common side effects of Viagra are (FDA, 2014-a): 

• Headaches

• Flushing

• Dizziness

• Upset stomach

• Nasal congestion

• Body aches

Serious side effects of Viagra happen less often and include: 

• Low blood pressure (hypotension) and fainting: Since Viagra makes your blood vessels relax, it can make your blood pressure drop, especially if you’re taking a type of medication called an alpha-blocker. This can cause you to collapse or faint. It can also trigger heart problems in people with a history of cardiovascular disease (FDA, 2014-a). 

• Hearing loss: Viagra can cause sudden hearing loss, usually in one ear. If it occurs, it usually happens within one to three days of starting the drug (McGwinn, 2010; Smith, 2013).

• Loss of vision: Viagra may cause a condition called non-arteritic anterior ischemic optic neuropathy (NAION), which can cause blurred vision and lead to vision loss. If it occurs, it usually happens in one eye within a few hours of taking the drug (Pomeranz, 2002).

• Priapism: Priapism is a painful, prolonged erection that you can’t get rid of, even if you’re not aroused. Viagra can cause priapism that lasts four hours or more, although a review of FDA data suggests this side effect is rare (Rezaee, 2020). 

• Bleeding: Viagra may cause bleeding since it can affect blood cells called platelets, which make your blood clot (FDA, 2014-a). 

Viagra and the generic of Viagra are available by prescription only—they are not sold over the counter. 

Oral tablets come in doses of 25mg, 50mg, and 100mg. Sildenafil also comes in an oral suspension and an injection form. 

The starting dose of Viagra is usually 50mg orally, taken between 30 minutes and four hours before sex. A healthcare provider may increase the dosage based on symptoms, side effects, and any other medications you are taking. 

You can take Viagra pills with food, but it may take longer to work if you take them with a high-fat meal.  

Viagra can cause adverse reactions if you combine it with other prescription drugs. Some examples of medications to avoid when you’re taking Viagra include (FDA, 2014-a):

• Heart medications: Viagra may be dangerous if you take it with certain cardiovascular medicines. These include nitrates (nitroglycerin) and blood pressure medications (especially alpha-blockers such as doxazosin). The combination can cause a dangerous and possibly fatal drop in your blood pressure. 

• HIV medications: Antiviral medications like ritonavir, which is often taken for HIV, may interfere with your liver’s ability to clear Viagra from your body, causing an increased risk of toxic effects. 

• Antibiotics and antifungals: Medications that treat bacterial and fungal infections, like erythromycin, itraconazole, and ketoconazole, may also interfere with your liver’s ability to get rid of Viagra. 

Viagra is more likely to cause adverse effects in people with certain underlying health conditions or risk factors. If you are in any of these groups, you should consult a healthcare provider before you use Viagra (FDA, 2014-a): 

• People with a known allergy to Viagra, Revatio, or sildenafil

• People with a higher risk of priapism (such as people with sickle cell anemia, leukemia, or Peyronie’s disease)

• Anyone taking nitrates or nitrites

• Anyone taking alpha-blockers or other blood pressure medications

• Individuals with heart conditions that are considered too risky for sexual activity (for example, heart valve disease like aortic stenosis)

• People with a history of low blood pressure, irregular heartbeat, or heart failure

• Anyone who has experienced a stroke or heart attack in the past six months

• People with a type of chest pain called unstable angina

• People who are pregnant

• People with liver or kidney problems

Getting an erection isn’t always easy—there are a number of steps that can go wrong and cause erectile dysfunction. Viagra is a helpful treatment for ED and typically causes only mild to moderate side effects. However, it may be dangerous when combined with certain medications or underlying conditions. Your healthcare provider can help you decide if Viagra is best for your needs. 

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Current version

February 04, 2022

Written by

Gina Allegretti, MD

Fact checked by

Steve Silvestro, MD

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About the medical reviewer

Steve Silvestro, MD, Ro

Dr. Steve Silvestro is a board-certified pediatrician and Associate Director, Clinical Content & Education at Ro.