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How Does Viagra Work?

Kelly Brown MD, MBA

Reviewed by Kelly Brown, MD

Written by Geoffrey Whittaker

Published 07/16/2019

Updated 03/06/2024

Your smartphone does a lot for you. It brings you the latest celebrity gossip, the current score of the game you’re not able to watch and it’ll even bring your groceries. And yet, most of us couldn’t begin to explain how smartphones work with more detail than the average tween.

The same is true of prescription erectile dysfunction medications — we know, nice segue.

Millions of men use the brand name medication Viagra® every year, making it the single-most popular medication used to treat erectile dysfunction in the country.

And we can see why — it works. Used at the proper dose, Viagra is considered very effective at helping men achieve and maintain an erection and is approved by the Food and Drug Administration for the treatment of ED.

It’s also not a bad thing if you can’t exactly explain how it works. Either way, the famous Pfizer little blue pill can help men aged 18 or older affected by ED to get hard and stay hard when aroused, making sexual activity easier and enhancing sexual performance.

But we’re pretty into knowing what we’re putting in our bodies, and we bet you are, too.

So if you’re wondering to yourself “how does Viagra work in the body?” let’s dig a little deeper than “pill makes peen go up,” because although Viagra might seem like an on/off switch for your penis, the way the medication works is fairly complex.

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Let’s just begin with this very obvious starting question: what does Viagra do? Is it something to do with ball bearings? Quarks? String theory?

Sadly, no. It’s a boring old biological reaction.

Viagra works by inhibiting the enzyme that’s responsible for controlling blood flow in and out of your penis when you’re sexually aroused. Viagra inhibits this phosphodiesterase type 5 (PDE5) enzyme — which explains Viagra’s (creatively named) classification as a PDE5 inhibitor.

Now, before we get into this in more detail, it’s important to briefly explain how erectile dysfunction happens and the role PDE5 plays in the process.

Erectile dysfunction, or ED, happens when you get aroused but the PDE5 enzyme stops a sufficient amount of the blood you need to get you hard from flowing into the corpora cavernosa.

Phosphodiesterase type 5 plays a normal role in making the penis flaccid after sex. It works by breaking down cGMP, which is another molecule that is responsible for dilating (widening) the arteries in the penis and increasing blood flow. If PDE5 breaks down too much cGMP, there is no longer sufficient blood flow to the penis for an erection — in other words, PDE5 can make getting erect and staying erect during sex difficult (or impossible).

  • By inhibiting PDE5, Viagra makes it easier for blood to flow into the blood vessels in your penis, allowing you to get — and stay — hard during sex.

  • More blood flow into the penis increases the pressure inside the penis, which makes it more difficult for blood to flow back out of the penis through the veins — a.k.a., it’s also harder to lose your erection.

  • This makes Viagra (as well as similar medications, such as Cialis® and Levitra®) a highly effective treatment for erectile dysfunction in most men.

  • Other erectile dysfunction medications, such as Cialis and Levitra, also work by inhibiting the PDE5 enzyme.

  • These medications differ from Viagra in how long their effects last — Tadalafil (generic Cialis), for example, can provide relief from erectile dysfunction for as long as 36 hours.

By the way, ED can range in severity — you could find it difficult to get fully erect when you’re sexually aroused but still get a moderate erection. If your ED is severe, your penis might stay entirely flaccid even when you’re aroused, making penetrative sex impossible.

Be sure to seek medical advice from a healthcare professional before you take Viagra and discuss any pre-existing health conditions and any over-the-counter or prescription drugs (such as nitrates) you currently are taking, as these may cause an interaction.

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If this is your first time taking Viagra, make sure you plan your sexual activities accordingly — it may not work exactly the way you’ve read online.

Depending on where you got your initial information, the internet suggests that a dose of Viagra could work minutes to hours after taking the pill, and to an extent that’s true. But sticking strictly to the FDA guidelines, Viagra typically kicks in about 30 to 60 minutes after you take it, and can work for up to four hours thereafter.

That timeframe may be affected by food, your weight, whether you find interesting porn or if your partner does that thing where they run their fingers through your hair.

All we can do is point to the window of effect, and remind you that everyone will have a slightly different experience. Oh, and if you’d like to learn more you can read our blog on how long Viagra lasts.

Viagra is an oral medication that comes in pill form. In the U.S., it’s prescribed as needed to men with ED.

As-needed Viagra is taken before sex, so you’ll need to do some planning. Be sure to take Viagra 30 minutes to one hour (but no more than four hours) before you plan to engage in sexual activity. And despite rumors you may have heard, snorting Viagra isn't the recommended way to take this drug (although people have wondered).

Also, you can take it on an empty stomach or with food, though if you’re hitting up a burger joint, know it may take Viagra longer to kick in when taken with fatty foods. For more tips, check out our blog on how to take sildenafil citrate (Viagra).

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FDA-approved Viagra is not without side effects, and like horniness in general, Viagra can mess with your stomach, your vision and your balance, and lead to unintended erections.

The FDA specifically calls out the following side effects:

  • Headaches

  • Stuffy nose

  • Flushing

  • Dizziness

  • Rash

  • Indigestion and upset stomach

It is also important to be aware of the serious side effects of Viagra. These may include:

  • Sudden loss of vision

  • Sudden hearing loss

  • Priapism (a painful erection that lasts for a long time)

If you experience any of these, seek immediate medical attention.

Finally, make sure you inform your healthcare provider of any medical condition (especially heart conditions or previous heart problems) that you may have, including:

  • High blood pressure

  • Recent heart attack

  • Other heart disease

  • Peyronie’s disease

  • Sickle cell anemia

Also inform them of any medications you’re taking, as some could cause problematic drug interactions, like a dangerous drop in blood pressure. Examples include nitroglycerin, alpha-blockers, recreational drugs like poppers and other ED medications like vardenafil or tadalafil.

Viagra isn't a miracle drug and it only works if you're sexually aroused. It's not a gas station sex pill; it's a legitimate medication prescribed to help men act on their feelings of attraction for their partners in a physical way — not make people attracted to things they aren't.

Sure, Viagra may seem like a magical elixir, but there are a few things it won’t do, like:

To read more about this ED medication, check out our article that answers the question of does Viagra keep you hard after coming?

Sildenafil citrate

Get hard for 95% cheaper than Viagra

Sildenafil, which is the active ingredient in Viagra and also sold as generic Viagra, is one of the most effective ED treatment options available. It works quickly and effectively, helping men enjoy enhanced sexual performance and relief from ED.

Here are some things to keep in mind as you’re beginning or continuing Viagra treatment:

  • YES it can help men achieve erections and sustain them for longer.

  • BUT it’s not going to magically cause erections — you still have to get aroused on your own.

  • ALSO you’ll need to be careful about side effects, especially if you have health issues.

  • SO if you think it may be what you’re looking for, talk to a healthcare professional about a prescription.

Our guide to what you should expect from Viagra and other ED medication lists all you need to know about the experience of using Viagra and other ED drugs, from the medication's average half-life to common side effects, onset of action and more.

2 Sources

  1. DRUGS@FDA: FDA-approved drugs. accessdata.fda.gov. (n.d.). Retrieved June 13, 2022, from https://www.accessdata.fda.gov/scripts/cder/daf/
  2. Erectile dysfunction & heart disease. Cleveland Clinic. (n.d.). Retrieved June 13, 2022, from https://my.clevelandclinic.org/health/diseases/15029-heart-disease—erectile-dysfunction#:~:text=and%20heart%20disease%3F-,There%20is%20a%20very%20strong%20link%20between%20erectile%20dysfunction%20and,at%20one%20point%2C%20had%20ED.
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Hims & Hers has strict sourcing guidelines to ensure our content is accurate and current. We rely on peer-reviewed studies, academic research institutions, and medical associations. We strive to use primary sources and refrain from using tertiary references. See a mistake? Let us know at [email protected]!

This article is for informational purposes only and does not constitute medical advice. The information contained herein is not a substitute for and should never be relied upon for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment. Learn more about our editorial standards here.

Kelly Brown MD, MBA
Kelly Brown, MD

Dr. Kelly Brown is a board certified Urologist and fellowship trained in Andrology. She is an accomplished men’s health expert with a robust background in healthcare innovation, clinical medicine, and academic research. Dr. Brown is a founding member of Posterity Health where she is Medical Director and leads strategy and design of their Digital Health Platform, an innovative education and telehealth model for delivering expert male fertility care.

She completed her undergraduate studies at University of North Carolina at Chapel Hill (go Heels!) with a Bachelor of Science in Radiologic Science and a Minor in Chemistry. She took a position at University of California Los Angeles as a radiologic technologist in the department of Interventional Cardiology, further solidifying her passion for medicine. She also pursued the unique opportunity to lead departmental design and operational development at the Ronald Reagan UCLA Medical Center, sparking her passion for the business of healthcare.

Dr. Brown then went on to obtain her doctorate in medicine from the prestigious Northwestern University - Feinberg School of Medicine and Masters in Business Administration from Northwestern University - Kellogg School of Management, with a concentration in Healthcare Management. During her surgical residency in Urology at University of California San Francisco, she utilized her research year to focus on innovations in telemedicine and then served as chief resident with significant contributions to clinical quality improvement. Dr. Brown then completed her Andrology Fellowship at Medical College of Wisconsin, furthering her expertise in male fertility, microsurgery, and sexual function.

Her dedication to caring for patients with compassion, understanding, as well as a unique ability to make guys instantly comfortable discussing anything from sex to sperm makes her a renowned clinician. In addition, her passion for innovation in healthcare combined with her business acumen makes her a formidable leader in the field of men’s health.

Dr. Brown is an avid adventurer; summiting Mount Kilimanjaro in Tanzania (twice!) and hiking the incredible Torres del Paine Trek in Patagonia, Chile. She deeply appreciates new challenges and diverse cultures on her travels. She lives in Denver with her husband, two children, and beloved Bernese Mountain Dog. You can find Dr. Brown on LinkedIn for more information.

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