A Complete Guide to Viagra® (Sildenafil) Side Effects

Erectile dysfunction, or ED, is a common sexual health condition that affects up to 40 percent of men by the age of 40.

Several medications are available to treat erectile dysfunction. Of these, the medication Viagra® (or, in its generic form, sildenafil) is arguably the most well-known and widely-used treatment on the market. 

Viagra works by increasing blood flow to your penis, making it easier for you to get and maintain an erection when you feel sexually aroused.

Used by millions of men in the United States alone, Viagra is a safe and effective medication for ED. Viagra's active ingredient, sildenafil, has been approved by the FDA for the treatment of ED since 1998, as well as conditions such as pulmonary arterial hypertension.

However, while Viagra is generally safe for most men, like almost all prescription medications, it does have the potential to cause side effects. 

Most of these Viagra side effects are mild and transient (meaning they tend to fade away as the medication exits your body), although some can become serious if you use other medications or have a pre-existing health condition.

Below, we’ve listed the common and uncommon side effects of sildenafil. We’ve also looked at the data behind many of these Viagra side effects to explain how and why they happen, as well as what you can do to manage them. 

Finally, we’ve discussed several drug interactions that you should be aware of if you’re thinking of using Viagra or generic sildenafil to treat erectile dysfunction.

The Most Common Side Effects of Viagra

Viagra has several common side effects. These side effects typically occur at the same time as the medication is active in your body (generally three to five hours), although some side effects may continue for several hours after Viagra’s active effects wear off.

Headaches

Headaches are one of the most common side effects of Viagra, affecting 25 percent of men who use this medication, according to the FDA.

The headaches caused by Viagra are usually mild and typically fade away as the drug becomes less concentrated in your bloodstream.

Other ED medications, such as Cialis® (tadalafil or generic Cialis) and Levitra®, are also linked to headaches. These drugs all work by expanding your blood vessels, which helps to improve blood flow to the erectile tissue in your penis.

This has the side effect of also increasing blood flow to other areas of your body. As your blood vessels increase in diameter, it can potentially contribute to headache pain by increasing blood supply to your head causing some people to have headaches.

As the effects of Viagra fade and your blood vessels gradually begin to constrict, it’s normal for any headaches you experience from the medication to become less intense.

Our guide to treating headaches from ED medication covers what you can do if you often get a headache after using Viagra. 

Most of the time, Viagra-induced headaches can be treated either by adjusting your dosage or by using over-the-counter pain relief.

Back Pain 

Some Viagra users experience muscle aches after using their medication. These can range in severity from a mild level of muscular pain to more significant, noticeable pain in a certain area, such as the lower back. 

According to clinical trial data, between two and four percent of men who use Viagra experience some degree of muscle pain.

Like headaches, muscle aches and pain that develop after using Viagra can normally be treated with over-the-counter pain relief medications.

If you have recurring, uncomfortable back pain or muscle aches after using Viagra, make sure to discuss this with your healthcare provider. Your healthcare provider might recommend a suitable form of pain relief or suggest using a lower dose of Viagra for ED treatment.

Rhinitis (Nasal Congestion)

Viagra can cause you to get a stuffy, partially blocked nose. Like most other side effects, this is a temporary issue that is most common while the medication is still in your system, although in some cases it can persist for several hours after the main effects of Viagra wear off.

Data from clinical trials shows that between four and nine percent of men who use Viagra have some amount of nasal congestion.

This side effect is a result of Viagra’s effects on blood vessels throughout your body. By causing your blood vessels to expand, Viagra can contribute to nasal obstruction, making it more difficult to breathe through your nostrils.

One small study published in the Tohoku Journal of Experimental Medicine shows that this side effect can occur even with a 50mg dose of Viagra.

Like other side effects, it may be possible to limit the effects of Viagra on your ability to breathe through your nose by reducing your dosage of the medication. 

Dizziness

As a vasodilator, Viagra can potentially cause a mild reduction in blood pressure. This may lead to feelings of dizziness and/or lightheadedness, including when standing suddenly.

Most of the time, any dizziness that’s caused by Viagra is mild and passes quickly as your body gets used to the effects of the medication.

If you frequently experience dizziness after using Viagra, let your healthcare provider know. Like many other common side effects of Viagra, you can often reduce or avoid dizziness by adjusting your dosage of this medication. 

Facial Flushing

Sildenafil, the active ingredient in Viagra, causes your blood vessels to widen, improving blood flow to your penis and making it easier to get an erection.

This can also cause blood vessels in other parts of your body to widen. When the blood vessels in your skin dilate, your skin can take on a red, flushed appearance. Some men who use Viagra notice this effect around their nose, cheeks and forehead.

Research shows that between 10 and 19 percent of men who use Viagra to treat ED experience flushing.

Just like headaches, facial flushing fades away on its own as the dose of sildenafil active in your body decreases. 

If you’re prone to facial flushing from Viagra, switching to a lower dose of medication may cause this side effect to become less intense and visible. Because facial flushing is a common adverse effect of all ED medications, switching to Cialis or Levitra may not prevent this from occurring. 

Dyspepsia (Indigestion/Heartburn)

Dyspepsia (indigestion or heartburn) is a common side effect of Viagra that can occur because of this medication’s effects on smooth muscle tissue throughout your body. 

After you take Viagra, the smooth muscle tissue in your penis starts to relax, leading to greater blood flow. 

This effect also occurs in other smooth muscle tissue, including the lower esophageal sphincter (LES), a group of muscles that separate your stomach and esophagus.

This may result in a small amount of stomach acid making its way from your stomach into your esophagus.

Heartburn from Viagra or other ED medications can be treated using over-the-counter antacids such as Gaviscon®, which creates a protective layer on the top of your stomach contents. 

If you experience mild heartburn or indigestion-related chest pain from Viagra, drinking a glass of water may also help to prevent discomfort.

If you frequently get indigestion/heartburn after using Viagra, consider discussing switching to a lower dose of the medication with your healthcare provider. 

It’s also important to avoid consuming too much alcohol with Viagra, as alcohol can further relax the lower esophageal sphincter and potentially contribute to heartburn. 

Nausea

Sildenafil, the active ingredient in Viagra, causes a small percentage of men to develop nausea shortly after it’s taken.

Nausea affects between two and three percent of men who use Viagra. In one four-year study of men who use sildenafil published in the journal Therapeutics and Clinical Risk Management, only one man out of 979 study participants reported nausea as a side effect.

Nausea from sildenafil is generally mild. Like other side effects, it most frequently occurs while the medication is active, with nausea and stomach discomfort typically fading away as Viagra’s effects wear off.

If you feel nauseous after using Viagra, consider talking to your healthcare provider about using a lower dose of the medication.

Visual Disturbances

Viagra is linked to several vision-related side effects, including blurred vision, abnormal vision (a noticeable color tinge to vision), decreased vision and even abrupt loss of vision.

Visual disturbances are most common among men who use Viagra at a dosage of 100mg. Only one to two percent of men report vision issues at 25mg and 50mg doses of Viagra, compared to 11 percent at a 100mg dose.

According to a scientific review published in the journal Progress in Retinal and Eye Research, most vision-related issues from Viagra are mild and transient, with problems typically occurring as the Viagra reaches its peak concentration in the body.

It’s important to inform your healthcare provider if you develop any changes in your vision after taking Viagra, or if you have a history of vision loss or eye issues such as non-arteritic anterior ischemic optic neuropathy (NAION).

Low Blood Pressure

Viagra is a vasodilator, meaning it can expand your blood vessels. This can reduce your blood pressure levels by a small amount. 

According to data from the FDA, people’s blood pressure drops by an average of 8.4/5.5 mmHg after taking a typical dose of Viagra. This reduction in blood pressure is mild and is unlikely to lead to any negative health effects in people with healthy, non-hypertensive blood pressure.

In short, if you’re healthy and don’t have any blood pressure issues, Viagra will affect your blood pressure, but not in a dangerous or concerning way.

If you have cardiovascular disease or hypertension, Viagra could lead to a sudden drop in blood pressure and have a more significant effect on your general health. 

It’s important to discuss this with your healthcare provider before using Viagra, particularly if you use medication to treat hypertension (high blood pressure), hypotension (low blood pressure) or any other cardiovascular health issue.

Less Common, More Serious Viagra Side Effects

Although serious side effects from Viagra are highly uncommon, they can still happen. Viagra has several uncommon side effects, including priapism and damage to the nerve that delivers electrical impulses from your eyes to your brain. 

It’s important to pay close attention to these side effects and notify your healthcare provider if you experience any issues. 

Priapism (Prolonged and/or Painful Penile Erection)

Priapism is a serious condition in which you experience a persistent, painful erection that lasts for several hours without any sexual stimulation. This type of prolonged erection can result in permanent damage to the erectile tissue inside your penis if it’s left untreated.

Cases of priapism tend to develop as a result of smooth muscle relaxation, which can increase blood flow to the penis. When blood can flow into the penis but not out, it can result in a painful, prolonged erection that may last for several hours.

Compared to other Viagra side effects, priapism is very uncommon. Many of the reported cases of priapism related to Viagra and other ED medications involve people taking overly large doses of their medication prior to sex, such as 200mg (twice the maximum recommended dose).

Priapism can cause a number of severe complications, including ischemia, hypoxia, cavernosal acidosis and permanent damage to the erectile tissue in your penis.

If you develop a painful or uncomfortable erection that persists for several hours, especially with little or no sexual stimulation, it’s important to seek medical help as soon as possible. 

Damage to the Optic Nerve

Although it’s extremely rare, erectile dysfunction drugs such as Viagra are linked to damage to the optic nerve, or nonarteritic anterior ischemic optic neuropathy.

Nonarteritic anterior ischemic optic neuropathy is a serious medical condition that can result in permanent damage to the eyes, including vision loss.

This issue affects a very small percentage of men who use Viagra, and may be a larger risk for people with existing eye issues or a "crowded" optic disc.

In a review published in the International Journal of Clinical Practice in 2006, researchers found that approximately 2.8 cases of NAION occur per 100,000 patient-years of Viagra use, making it an extremely rare potential side effect.

To reduce your risk of developing NAION, it’s important to inform your healthcare provider if you have any existing vision-related health issues before using Viagra, or if you experience any loss of vision while using Viagra or similar medications to treat ED.

Sudden Loss of Hearing

An extremely small percentage of men who used Viagra have reported a condition that’s known as sudden sensorineural hearing loss (SSHL). This condition involves damage to the inner ear that can, in some cases, cause permanent loss of hearing. 

In addition to hearing loss, Viagra can cause other hearing-related conditions, such as ringing in the ears (tinnitus).

Hearing issues from Viagra are uncommon. It’s important to tell your healthcare provider if you experience any changes in your hearing after taking Viagra, such as sudden loss of hearing or reduced hearing sensitivity. 

Interactions Between Viagra and Cardiovascular Medications

Sildenafil, the active ingredient in Viagra, can interact with some medications used to treat high blood pressure, heart disease and other cardiovascular health issues. 

For example, Viagra and other ED medications can interact with nitrates used to manage blood pressure and treat congestive heart failure, as well as medications such as alpha-blockers.

When used at the same time, these medications may contribute to a sudden, potentially severe drop in blood pressure that can seriously affect your health.

You should not use Viagra or other ED drugs if you currently use any type of nitrate medication, such as nitroglycerin, isosorbide dinitrate or isosorbide mononitrate.

Viagra should also not be taken with recreational drugs such as “poppers,” which often contain ingredients such as amyl nitrate.

When used with ED medications, nitrates can contribute to a severe decline in blood pressure that may cause you to feel dizzy or faint. In some cases, interactions between ED medications and other prescription drugs may cause heart attack or stroke.

To reduce your risk of experiencing interactions while using Viagra, it’s important to inform your healthcare provider about all medications you currently use or have recently used before taking Viagra or other ED treatments. 

Pre-Existing Medical Conditions & Viagra

Unfortunately, certain medical conditions may increase your likelihood of developing side effects from Viagra and other ED medications.

To keep yourself safe while using Viagra, it’s important to inform your healthcare provider about any pre-existing conditions before you consider this medication.

It’s especially important to inform your healthcare provider if you:

• Have any type of heart issue, such as heart failure, angina, narrowing of the aortic valve, irregular heart beat, or have previously suffered a heart attack or stroke.

• Have pulmonary hypertension (high blood pressure in the blood vessels that supply your lungs), uncontrolled high blood pressure, or low blood pressure.

• Have any type of medical condition that affects your blood cells, such as leukemia, sickle cell anemia or multiple myeloma.

• Have any type of eye problem or vision loss, such as non-arteritic anterior ischemic optic neuropathy or retinitis pigmentosa, a genetic eye disease.

• Have a deformed penis shape or a condition such as Peyronie’s disease, which involves damage to the tissue inside your penis. 

• Have bleeding problems, liver problems, kidney problems, stomach ulcers or are actively on dialysis.

Onset of Action for ED Medication: How Long Does It Take?

Most erectile dysfunction drugs take 30 to 60 minutes to work. Currently, the fastest-acting ED medication is avanafil (Stendra®), a second-generation ED treatment that produces noticeable effects in 15 to 30 minutes.

Sildenafil, or Viagra, takes approximately one hour to start working and should be taken about 60 minutes before you plan to have sex.

Most of the time, the effects of sildenafil will begin to appear 30 to 60 minutes after you take a standard dosage of this medication. However, eating a large meal that’s high in fat can delay the effects of sildenafil and reduce its total concentration in your bloodstream.

Tadalafil, the active ingredient in Cialis, can become active in your body within 15 minutes, but typically reaches its peak concentration after two hours.

Vardenafil, the active ingredient in Levitra, starts working in approximately the same amount of time as sildenafil and should be taken one hour before sex.

Regardless of the specific medication you use, it’s best to take your ED medication around one hour before you plan to have sex. Prepare ahead of time and you’ll experience the medication’s full effects when you and your partner become intimate.

As always, if your healthcare provider provides a specific recommendation for when to take your medication, it’s important to follow their advice.

Most ED drug manufacturers recommend taking sildenafil, tadalafil, vardenafil or avanafil with a glass of water on a relatively empty stomach (or after a small or normal-sized meal).

Half-Lives of ED Medications: How Long Do They Last?

A drug’s half-life is the amount of time required for the concentration of the medication in your body to fall to half of its peak.

For example, a 50mg dose of sildenafil (Viagra) will be reduced to a potency of approximately 25mg after one half-life has passed.

The half-life of a medication determines how long it will stay active in your body. Generally, ED drugs still provide some effects after one half-life, and gradually become less effective as they are eliminated from your body.

After about two to three half-lives have passed, most medications for ED will no longer provide any noticeable effects. 

ED medications can vary significantly in terms of half-life, meaning some drugs last for longer than others. 

Currently, the longest-lasting medication for ED is tadalafil, the active ingredient in Cialis. The half-life of tadalafil is approximately 17.5 hours, and a normal dose of tadalafil can continue to provide relief from erectile dysfunction for up to 36 hours. 

Other ED medications have shorter half-lives:

• Sildenafil, or Viagra, has a half-life of approximately three to five hours. A typical dose of sildenafil will provide relief from erectile dysfunction for four hours, making it ideal for single-night use.

• Vardenafil, or Levitra, has a half-life of approximately four to five hours. A typical dose of vardenafil can provide relief from erectile dysfunction for four to eight hours, making it another good choice for single-night use. 

• Avanafil, or Stendra, has a half-life of approximately five hours. Similar to sildenafil and vardenafil, Stendra is recommended for use as a single-night ED treatment.

Since ED can vary in severity and people’s sexual needs differ, there’s no one-size-fits-all “best” erectile dysfunction medication for everyone. 

If you’re not sure which type of ED medication to use, it’s best to talk to your healthcare provider about your options. Your healthcare provider might recommend a specific ED medication based on your health history and personal needs.

The Bottom Line on Viagra Side Effects 

For most men, Viagra is a safe and effective medication that can make getting and maintaining an erection an easier, less stressful experience.

However, like all medications, Viagra can cause side effects. It’s important to be aware of these side effects before you start using Viagra, and to talk to your healthcare provider if you develop any side effects while using this medication in the treatment of erectile dysfunction. 

We offer both sildenafil and brand-name Viagra online as part of our range of ED medications, following a consultation with a licensed healthcare provider who will determine if a prescription is appropriate. 

You can also learn more about sildenafil and other options for treating ED in our detailed guide to the most common erectile dysfunction treatments.