Get a free visit for ED treatment. Start now

Last updated: Dec 03, 2021
4 min read

How does Viagra (sildenafil) work?

chimene richa

Medically Reviewed by Chimene Richa, MD

Written by Michael Martin

Disclaimer

If you have any medical questions or concerns, please talk to your healthcare provider. The articles on Health Guide are underpinned by peer-reviewed research and information drawn from medical societies and governmental agencies. However, they are not a substitute for professional medical advice, diagnosis, or treatment.

You’ve probably heard of Viagra, also known as the “little blue pill.” But how much do you know about how it works? 

Contrary to popular belief, Viagra doesn’t simply give you an erection—rather, it helps you get one (and keep it) when you’re in the appropriate mood and need it most.  

Get $15 off your first month of ED treatment

If prescribed, get ED treatment delivered discreetly directly to your door.

Learn more

What is Viagra?

Also known under the generic name sildenafil, Viagra (see Important Safety Information) is an oral medication that treats erectile dysfunction (ED). Initially, sildenafil was developed to treat hypertension (high blood pressure), but it wasn’t that effective in clinical trials. However, it did do one thing: men who took it got more erections. 

Approved by the U.S. Food and Drug Administration (FDA) in 1998, Viagra was the first oral drug approved to treat ED in the United States. Sildenafil is now also available under the brand name Revatio to treat pulmonary arterial hypertension, a rare type of high blood pressure that affects the lungs (Smith, 2021).

How does Viagra work?

Erections seem pretty basic, but they’re surprisingly complicated. Getting an erection involves cooperation between your heart, blood vessels, hormones, nerves, and even your mood. 

During an erection, chemicals in the body cause tissues in the penis to relax. As a result, blood flows into the penis gets trapped (you’ll notice much more blood in an erect penis than when it’s flaccid). Eventually, the blood gets released, the erection subsides, and blood flow down there returns to normal. 

Viagra works by blocking what’s called PDE5 (phosphodiesterase type 5), an enzyme in the body that breaks down chemicals responsible for erections. When PDE5 is blocked, these chemicals don’t get broken down, and as a result, tissues in the penis stay relaxed and engorged with blood.

Viagra, Cialis (generic name: tadalafil; see Important Safety Information), Levitra (vardenafil), and Stendra (avanafil) are all drugs in the PDE5 inhibitor family (Smith, 2021).

It’s important to remember that Viagra is highly effective for ED, but is not a magic pill: you need to feel sexually aroused for it to work.

What is erectile dysfunction?

Many things fall into the ED category, including erections that are softer, less frequent, don’t last as long, or there’s a lack of morning erections. ED isn’t just about not being able to get hard—it also involves how you and your partner feel about your sex life.

ED can be frustrating, but it’s very common. Roughly 30–50 million men in the United States have erectile dysfunction, and most guys will experience it at some point in their lives. It’s essential to address ED early on as it can also be a sign of potentially serious conditions like (Sooriyamoorthy, 2021):

How long does Viagra last?

Viagra starts working within 30–60 minutes, so you should take it at least that long before sexual activity. For some men, it starts working more quickly. 

Viagra is effective for about 4–5 hours. Your personal mileage will vary depending on your age, the dosage, other medications, and overall health.

Side effects of sildenafil

Common side effects of Viagra and other ED medications include (DailyMed, 2020):

  • Headache
  • Facial flushing
  • Nasal congestion
  • Upset stomach
  • Back pain
  • Dizziness
  • Skin rash

Other less common side effects include temporary vision impairment, vision loss, chest pain, shortness of breath, low blood pressure, and fainting. 

A well-known but rare reaction to Viagra is priapism, a painful erection that won’t go away. If an erection lasts more than a few hours, it can damage the penis (that’s why ED medications have warnings about erections “lasting longer than four hours”). If you experience priapism or other serious side effects, seek medical attention ASAP. 

Viagra by itself can also lower blood pressure. If you already have low blood pressure or are taking medication to treat high blood pressure, talk with a healthcare provider before taking Viagra. 

Risks of taking Viagra

Treatment with PDE5 inhibitors is not safe for everyone. For example, people taking certain drugs for heart disease (like nitrates) should not use Viagra. 

Nitrates increase what’s called nitric oxide, which triggers the release of erection-inducing chemicals. Problems arise if you take ED meds with nitrates––like amyl nitrite (poppers). The combination can cause too much blood vessel relaxation (vasodilation). This can potentially lead to a dangerous, even fatal, drop in blood pressure.

People with heart conditions, chest pain, or a history of heart attack or stroke, heart attack should check with a medical professional before taking Viagra. If you’ve experienced allergies or a hypersensitivity reaction to Viagra, you shouldn’t use the medication again (DailyMed, 2020).

Medication isn’t the only answer for ED. Certain lifestyle changes can also help, including exercise, a better diet, and managing stress. You may feel embarrassed to talk about ED, but don’t be. ED affects millions of men, and you owe it to yourself to speak with an expert about your concerns. Get the medical advice you need to take back control of your health.

References

  1. DailyMed. (2020). Viagra- sildenafil citrate tablet, film-coated. Retrieved on Nov. 16, 2021 from https://dailymed.nlm.nih.gov/dailymed/lookup.cfm?setid=a2a9f459-e692-4e85-83b0-a35fbf35e91b.
  2. Smith, B. P., Babos, M. (2021). Sildenafil. [Updated 2021 Jun 29]. In: StatPearls [Internet]. Retrieved on Nov. 16, 2021 from https://www.ncbi.nlm.nih.gov/books/NBK558978/.
  3. Sooriyamoorthy, T., Leslie, S. W. (2021). Erectile dysfunction. [Updated 2021 Aug 12]. In: StatPearls [Internet]. Retrieved on Nov. 16, 2021 from https://www.ncbi.nlm.nih.gov/books/NBK562253/.