Sildenafil Side Effects: What To Expect

February 03, 2023
4 mins

Since its approval by the Food and Drug Administration in 1998, Viagra®, known generically as sildenafil, has been prescribed to millions of men for erectile dysfunction. 

You’ve almost certainly heard of sildenafil before, although you're probably more familiar with the brand name Viagra®. Sildenafil is the active ingredient in Viagra, which has dominated the erectile dysfunction landscape for twenty years, becoming a household name in the few years after approval.

Today, sildenafil and Viagra combined are still the most popular erectile dysfunction medicine prescribed in the U.S.

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Sildenafil has a significant impact on your body, working to increase blood flow to the penis and helping to maintain stronger erections for longer. Because of its capabilities, it requires a prescription from a licensed doctor to purchase at a pharmacy. (Interestingly, sildenafil is available over-the-counter in some countries.) 

While sildenafil and Viagra are considered safe for most men, this medication does have known side effects in some men, just like most medications, and it isn't a fit for everyone. 

What To Know About Sildenafil Side Effects

  • Sildenafil is the active ingredient in Viagra and a PDE5 inhibitor much like Cialis (tadalafil) and Levitra (vardenafil). Sildenafil is available as a generic medication today and is effective in treating the symptoms of erectile dysfunction for most men who use it.

  • Sildenafil's most common side effects include flushing, headache, body aches, and stomach discomfort, though all of these occur in a quarter of men or fewer. They can often be improved or eliminated with a lower dose.

  • Dangerous side effects are possible for men taking sildenafil who also have hypertension, cardiovascular conditions, and those who are taking medications for these conditions. Talk to your doctor about your health before trying sildenafil.

What Effect Does Sildenafil Have On the Body? 

Once you know exactly what sildenafil does, it's easier to understand the potential side effects and why they can happen.

Sildenafil is in a class of drugs known as phosphodiesterase type 5 (PDE5) inhibitors. Almost all of the prescription drugs used to manage erectile dysfunction belong to this class, including tadalafil (Cialis®) and vardenafil (Levitra®)

Sildenafil and these drugs works by releasing the body's own "braking" mechanism on blood flow, allowing more blood to flow into the penis and facilitating an erection.

  1. When you experience mental or sensory sexual stimulation, you enter into a state of arousal.

  2. Once aroused, your brain and certain glands release chemical messaging substances that travel throughout your body to prepare you for sexual activity. 

  3. One of these chemical messengers is a compound called nitric oxide. It helps to increase the production of cyclic guanosine monophosphate (cGMP) in blood vessels, which basically tells your muscles to relax and your blood vessels to expand, or dilate. These changes increase blood flow throughout your body, and especially to your penis in order to create an erection.

  4. PDE5 is an enzyme located in the walls of your blood vessels that regulates cGMP, reversing its effects and restoring your muscles and blood vessels to normal after an erection or ejaculation.

  5. Sildenafil or any of the other PDE5 inhibitors block this enzyme from performing its normal function, keeping your blood vessels dilated, muscles relaxed, and erection firm for longer. It is essentially over-riding the body's normal check-and-balance system on erections and blood flow.

PPDE5 inhibitors like Viagra (sildenafil), Cialis (tadalafil), and Levitra (varde

nafil) have been used by millions of men safely and effectively since approval over twenty years ago. But side effects are possible.

What Are the Possible Side Effects of Sildenafil?

Sildenafil is safe for most men, but for those with underlying medical conditions, it can cause issues. 

The most significant impact that sildenafil has on your body is that it increases blood flow. As a result, you can experience a variety of minor side effects with sildenfail, including:

  • Headaches

  • Stuffy or runny nose

  • Upset stomach

  • Diarrhea

  • Ringing in your ears

  • Nosebleeds

  • Prolonged erections

  • Sensitivity to light

  • Rash

Most of these side effects are minor and not common.

According to one four-year study of sildenafil, the most common sildenafil side effects were headaches (28%), flushing (21%), dizziness (8%), abdominal pain (6%), and nasal congestion (5%). 

The most dangerous side effects of sildenafil are when it’s used in combination with other drugs. There is a long list of potential lethal interactions when sildenafil is mixed with other medications. Tell your prescribing healthcare professional all of the other drugs that you're currently taking, especially if they have any effect on your blood. 

The most dangerous sildenafil drug interactions involve nitrates and medications for high blood pressure and chest pain. Taking these drugs in combination with sildenafil can result in dangerously low blood pressure that may require hospitalization due to dizziness, fainting, or even a heart attack or stroke. 

When using sildenafil, seek immediate medical help if you experience the following serious side effects, as they may be a sign of a medical emergency including an allergic reaction or cardiovascular distress:

  • Flushing in the face, neck, chest, and body

  • Nausea

  • Dizziness

  • Muscle pains

  • Chest pain (angina) or back pain

  • Blurred vision or vision loss

  • Sudden decrease in hearing or total hearing loss

  • Trouble breathing

  • Swelling of the lips, tongue, and/or throat

What To Do If You Experience Side Effects on Sildenafil 

It’s generally unlikely that you will encounter lasting side effects when taking sildenafil. The good news is that sildenafil's side effects generally only last as long as the drug is in your system. 

While the drug can stay in your system for as long as 24 hours, its primary capabilities are in the 4-6 hours after taking it. Sildenafil's effects can vary based on on your age, metabolism, and your dose. 

Drinking more water can help your body accelerate sildenafil filtration and expulsion.

Sildenafil does not negatively interact with most over-the-counter medications, so for some minor side effects like headache, muscle ache, or other pain, ibuprofen or acetaminophen should be fine. For an upset stomach, indigestion, nausea, or diarrhea, over the counter stomach medicines should not affect sildenafil.

If you're concerned or have questions about sildenafil side effects, ask your doctor about your symptoms first. 

Can You Prevent Sildenafil's Side Effects From Happening? 

There isn’t much that you can do to prevent sildenafil's possible side effects, but you may be able to reduce their severity. For starters, if you experience a side effect on sildenafil, talk to your doctor about reducing your sildenafil dose. 

The most commonly prescribed dose of sildenafil is 50 mg, but your doctor may prescribe the maximum dose of 100 mg if lower doses aren’t cutting it.

If you're taking either of these doses, talk to your doctor about trying 25 milligram of sildenafil instead. It’s possible that this reduction may reduce or eliminate side effects.

The Takeaway 

Several side effects have been associated with taking sildenafil, but they're seen in a minority of cases.

Most guys who take medications that might interact with sildenafil will be warned by their prescribing physician ahead of time, and if sildenafil is unsafe due to existing medical conditions, the doctor likely won't prescribe sildenafil in the first place.

The most important thing is to be transparent with your prescribing clinician before taking sildenafil or Viagra. Sildenafil is not suitable for many men with high blood pressure or cardiovascular conditions and those taking medications for those conditions.

In the event that you do experience minor side effects like flushing or a sildenafil headache, side effects should diminish within hours as the drug exits your system.

Curious if erectile dysfunction medication is right for you? Find out the easy way with an online consult from Rex MD and medications delivered to your door, if approved.


FDA approves Viagra |

Phosphodiesterase-5 (PDE5) Inhibitors In the Management of Erectile Dysfunction | NCBI

The physiology of sexual arousal in the human female: a recreational and procreational synthesis. | PubMed

The role of nitric oxide in penile erection | PubMed

Cyclic guanosine monophosphate mediates penile erection in the rat | PubMed

Four-Year Review of Sildenafil Citrate. | NCBI

Sildenafil (Oral Route) Side Effects | Mayo Clinic

How Long Does Viagra Last & Stay in Your System? | MedExpress

Sildenafil citrate 100 mg starting dose in men with erectile dysfunction in an international, double-blind, placebo-controlled study: effect on the sexual experience and reducing feelings of anxiety about the next intercourse attempt | PubMed

Do food and dose timing affect the efficacy of sildenafil? A randomized placebo-controlled study | PubMed

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