Medically reviewed by Vicky Davis, FNP
Written by Our Editorial Team
Last updated 10/21/2022
Sildenafil, the active ingredient in Viagra®, is a common medication that’s used to treat erectile dysfunction (ED) and pulmonary arterial hypertension (PAH).
If you’ve been diagnosed with erectile dysfunction, your healthcare provider may prescribe you sildenafil to improve your erections and sexual performance.
If you’re affected by pulmonary arterial hypertension, your healthcare provider may recommend sildenafil on its own or with other medication to lower blood pressure in your lungs and improve your lung function.
Sildenafil is one of several erectile dysfunction medications in use today. It’s a fast-acting drug that, for most people, is safe and effective. However, like other medications, it can cause some side effects and has several interactions that you should be aware of before use.
Below, we’ve explained what sildenafil is and what it’s typically used for. We’ve also discussed alternatives to sildenafil, including several other medications that are available to treat erectile dysfunction.
Sildenafil belongs to a class of medications called phosphodiesterase type 5 inhibitors, or PDE5 inhibitors. It comes in tablet form and requires a prescription.
Medications like sildenafil work by causing the smooth muscle of your vascular system to relax. This improves blood flow in certain parts of your body and reduces your blood pressure levels.
Sildenafil is sold as a generic medication and under several brand names. You may have heard of oral sildenafil under the brand names Viagra or Revatio®.
The most common uses for sildenafil include treating erectile dysfunction and pulmonary arterial hypertension, a form of high blood pressure that affects the blood vessels inside your lungs.
Sildenafil is one of several medications available to treat ED. Others include tadalafil (the active ingredient in Cialis®), vardenafil (Levitra®) and avanafil (Stendra®).
Sildenafil is best known as a treatment for erectile dysfunction, or ED. Originally sold under the brand name Viagra, sildenafil came onto the market in 1998 as the first mainstream medication for treating ED and improving sexual function in men.
Erectile dysfunction is a common issue that affects men of all ages and backgrounds. According to the National Institute of Diabetes and Digestive and Kidney Diseases, about 30 million men in the United States are affected by ED.
As an ED treatment, sildenafil works by increasing blood flow to the erectile tissue found inside your penis.
Erections are all about healthy blood flow. When you feel sexually aroused, impulses from your brain and local nerves around your penis signal to the muscles that control blood flow into your corpora cavernosa -- the pair of cylinder-shaped areas of erectile tissue in your penis.
As these muscles relax, blood starts to flow into your penis, creating pressure that increases its size and makes it feel firmer to the touch.
In order to keep your penis firm during sex, the tunica albuginea -- a fibrous covering that wraps around the corpora cavernosa -- contracts. This traps the blood inside your penis and sustains your erection until you reach orgasm and ejaculate.
By dilating the arteries that supply blood to your penis, sildenafil makes it easier for this process to take place, helping you to get and sustain an erection during sex.
It’s worth keeping in mind that sildenafil won’t cause you to feel sexually aroused without sexual stimulation, nor will it give you an erection if you’re not in the mood for sex.
Instead, its effects as a medication are purely physical, with no evidence that it affects your sex drive or level of interest in sexual activities in any meaningful way.
Interestingly, sildenafil wasn’t initially developed as a treatment for erectile dysfunction. Instead, it was under investigation as a treatment for hypertension and angina. During testing, the team studying sildenafil noticed that it often caused erections as a side effect.
Today, sildenafil is still available as Viagra. It’s also available as a generic medication for erectile dysfunction. As a treatment for ED, sildenafil is available in a range of different dosages from 25 to 100mg.
Sildenafil is a fast-acting, convenient medication for treating erectile dysfunction. On average, a single dose of sildenafil starts working in approximately 30 minutes and provides relief from ED for around for hours.
For best results, most experts recommend taking sildenafil around one hour before the time you plan to have sexual intercourse.
In addition to sildenafil, several other medications are available to treat erectile dysfunction:
Tadalafil. The active ingredient in Cialis, tadalafil is a long-lasting ED medication that can provide relief from erectile dysfunction for up to 36 hours per dose.
Vardenafil. The active ingredient in Levitra, vardenafil has similar effects to sildenafil and typically lasts for approximately four hours per dose.
Avanafil. Available as Stendra, avanafil is a second-generation PDE5 inhibitor that’s less likely to cause certain side effects than older ED medications.
Some of these medications, such as tadalafil, are available in a daily dose form, allowing you to use them on a daily basis for long-lasting relief from ED symptoms.
You can learn more about these medications, how they work and their unique advantages in our full guide to the most common erectile dysfunction treatments and drugs.
Although sildenafil is best known as a medication for erectile dysfunction, it’s also used to treat a condition called pulmonary arterial hypertension, or PAH.
Pulmonary arterial hypertension is a condition in which blood pressure in the vessels that supply your lungs increases. The walls of the arteries in this part of your body may become thicker and more narrow, restricting blood flow and affecting your heart function.
Over time, pulmonary hypertension tends to worsen, which may damage your heart and reduce blood circulation throughout your body.
Unlike erectile dysfunction, pulmonary arterial hypertension isn’t very common. According to the American Lung Association, only around 500 to 1,000 cases of PAH are diagnosed in the United States every year.
Sildenafil is one of several medications used to treat PAH. It works by helping the blood vessels in your lungs to relax and widen, reducing blood pressure and improving blood flow between the lungs and your heart.
As a treatment for PAH, sildenafil is typically prescribed in a 20mg dosage. It’s available under a variety of brand names, including Revatio and others.
Sildenafil (generic Viagra) is used by millions of men of all ages and backgrounds. Although it’s generally a safe, effective medication, it can cause certain side effects and interactions, whether it’s used to treat erectile dysfunction or pulmonary arterial hypertension.
Common side effects of sildenafil include:
Changes in color vision
Myalgia (muscle pain)
Difficulty falling asleep
Increased sensitivity to light
Most side effects caused by sildenafil are minor and temporary, meaning they should gradually fade away as the medication leaves your body.
If you notice any persistent or bothersome side effects while using sildenafil, it’s important to let your healthcare provider know. They may suggest adjusting your dosage or making changes to the way you use this medication.
Although uncommon, sildenafil may also cause other side effects, including some that are more serious. It’s important to pay attention for these potential adverse effects and let your healthcare provider know if they occur.
Potentially serious side effects of sildenafil include:
Changes in your ability to see, such as blurred vision or sudden loss of vision
Hearing changes, such as sudden decrease in hearing sensitivity or loss of hearing
Feelings of dizziness, lightheadedness or fainting
Itching, burning or other discomfort while urinating
Chest pain and/or shortness of breath
In rare cases, sildenafil and other medications for the treatment of erectile dysfunction may lead to priapism -- a long-lasting, painful erection. If untreated, this side effect can potentially damage the tissue inside your penis.
Make sure to access emergency medical attention as soon as you can if you develop a painful, persistent or uncomfortable erection that lasts for several hours after taking sildenafil.
Although extremely uncommon, sildenafil may cause serious cardiovascular problems, such as stroke, heart attack or irregular heartbeat, in men with cardiovascular disease, congestive heart failure or other cardiovascular health issues.
To reduce your risk of side effects, make sure to inform your healthcare provider if you have any heart issues or other health problems before using sildenafil treatment for ED.
In addition to causing some side effects, sildenafil and other medications for sexual dysfunction may interact with other medications, supplements, herbal products and other substances.
Most notably, sildenafil can interact with medications for treating high blood pressure and heart disease, including nitrates and alpha-blockers. It can also interact with recreational drugs that affect blood pressure, such as amyl nitrate, amyl nitrite and butyl nitrate “poppers.”
Used together, these medications can cause a sudden drop in arterial blood pressure that may cause fainting and injury.
To reduce your risk of experiencing drug interactions, make sure to fully inform your healthcare provider about any medications, supplements or recreational drugs you use before you discuss sildenafil or other phosphodiesterase-5 inhibitors for ED.
As a PDE5 inhibitor, sildenafil increases blood flow and reduces blood pressure in certain parts of your body, such as the blood vessels inside your penis and lungs.
Whether you’re prescribed brand-name Viagra or generic sildenafil for the treatment of ED, it’s important to take your medication as prescribed. Make sure to carefully follow your healthcare provider’s instructions and inform them if you experience any side effects.
We offer sildenafil online as part of our range of erectile dysfunction medications, following an online consultation with a physician who will determine if a prescription is appropriate.
Interested in learning more about treating ED? Our full guide to erectile dysfunction treatment options goes into detail about the best ways to maintain an erection and improve your sexual performance, from medications to psychotherapy, pelvic floor exercises and more.