How Does Viagra Work?

With more than two million annual prescriptions in the United States alone, Viagra is the most common medication used to treat erectile dysfunction.

Used at the proper dose, Viagra is highly effective. It can help men of all ages affected by ED to get and maintain an erection when aroused, making sexual activity easier and enhancing sexual performance in general.

Although Viagra might seem like an on/off switch for your penis, the way the medication works is fairly complex. Below, we’ve explained how Viagra works to treat erectile dysfunction, as well as the process your body goes through to get and keep an erection during sexual activity.

How Erections Work

Before we get into the specifics of how Viagra works to help you get an erection, it’s important to cover how erections actually happen.

While erections physically affect your penis, they’re actually part of a long biological process that begins in your brain. The process involves everything from your brain to your spine, veins, lungs and the erectile tissue of your penis.

In short, pitching a tent is, at least from a biological perspective, much more complicated than it usually seems . 

The process starts in the brain. When you’re sexually stimulated, the paraventricular nucleus — a nucleus in your hypothalamus — sends a signal to the nerves in your penis. This signal travels down your spinal cord quickly, resulting in the start of a rapid, complicated physical reaction.

After the nerves in your penis receive this signal, they release nitric oxide. This chemical relaxes the soft tissue of the corpora cavernosa — a pair of long, sponge-like areas of erectile tissue that fill with blood in order to give you an erection.

At this point, blood starts to flow into the corpora cavernosa. As more blood flows into the tissue, your penis starts to become firmer. Your penis contains around eight times as much blood when it’s erect than when it’s flaccid (when it’s fully erect, there’s about 130ml of blood in there).

After the corpora cavernosa are filled with blood, a fibrous envelope called the tunica albuginea tightens around the erectile tissue. This helps to keep blood in the penis and causes the level of pressure to increase, resulting in an erection.

This process continues as long as you’re aroused, with blood inside the corpora cavernosa and your penis in a firm, erect state. 

After you orgasm and ejaculate, your body starts to reverse this process. Your body releases an increased amount of noradrenaline, a stress hormone. This makes the arteries that supply blood to your penis contract, slowing the flow of blood into the corpora cavernosa.

At the same time, the tunica albuginea that controls blood flow out of your penis relaxes, letting blood flow back out of your penis. 

This process depends on several different parts of your body, from your brain to a healthy heart and cardiovascular system. If one part of the process doesn’t work properly, it can prevent you from getting and maintaining an erection when you’re sexually aroused. 

How Viagra Works

Viagra works by inhibiting the enzyme that’s responsible for making blood flow out of your penis when you’re sexually aroused. Specifically, Viagra inhibits the phosphodiesterase type 5 (PDE5) enzyme. 

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

Erectile dysfunction, or ED, happens when the PDE5 enzyme stops a sufficient amount of blood from flowing into your corpora cavernosa when you’re aroused. 

For men without erectile dysfunction, PDE5 plays a normal role in making the penis flaccid after sex. However, in men with erectile dysfunction, the actions of PDE5 can make getting erect and staying erect during sex difficult or impossible. 

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.

By inhibiting PDE5, Viagra makes it easier for blood to flow into your penis, allowing you to get and stay hard during sex. It also reduces the risk of blood flowing back out of your penis during sex, meaning you’re less likely to lose your erection than normal. 

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 the amount of time their effects last — CIalis, for example, can provide relief from erectile dysfunction for as long as two days. 

While PDE5 is a major factor in preventing you from getting an erection, it isn’t the only thing that can contribute to erectile dysfunction. You might also find it difficult to get and stay hard if you have:

  • Hormonal issues. Hormonal issues, such as low testosterone, can affect your level of sexual interest. In some cases, this could worsen ED. If your erectile dysfunction is the result of low testosterone or other hormonal issues, Viagra might not be fully effective.

    Our guide to testosterone and erections covers this issue in more detail and lists tactics that you can use to improve your sexual performance.

  • High blood pressure. High blood pressure is one of the most common physical causes of erectile dysfunction. If you have high blood pressure, it can become more difficult for the arteries that supply blood to the penis to properly dilate.

    Our guide to high blood pressure and erectile dysfunction explains this in more detail, with a list of approaches for lowering your blood pressure and improving your general health.
  • Heart disease. Certain heart conditions can affect the blood supply to your penis and make getting an erection more difficult. For example, atherosclerosis (hardening of the arteries), can reduce blood flow and make medications like Viagra less effective.
  • Psychological causes. Some cases of erectile dysfunction are caused by factors such as depression and anxiety. These factors are unrelated to PDE5, meaning that Viagra and other ED drugs might not be totally effective as treatment options.

    Our guide to the psychological causes of ED dives into this issue in more detail, with a full list of psychological factors that can contribute to and cause erectile dysfunction.
  • Porn consumption. Believe it or not, watching a significant amount of porn could have the potential to contribute to erectile dysfunction. This is called “porn-induced ED” and could be a potential cause of ED in many younger men.

    Our guide to porn-induced ED explains how this occurs in more detail, as well as what you can do to prevent porn from interfering with your ability to get an erection. 

Finally, erectile dysfunction can also occur incidentally if you’re feeling tired, stressed or simply aren’t in the mood for sexual activity. 

Learn More About Viagra

Sildenafil, the active ingredient in Viagra, is one of the most effective treatments available for erectile dysfunction. It works quickly and effectively, helping men of all ages enjoy enhanced sexual performance and relief from ED.

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. 



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.