How does Viagra (sildenafil) work?

You’ve probably heard of Viagra (sildenafil), often called the “little blue pill.” Even if you don’t have erectile dysfunction (ED), you’re probably familiar with it as it’s one of the most recognized ED medications on the market.

While many know the name, there are still quite a few misconceptions about how Viagra actually works. The big one? It's not a magic pill that instantly gives you an erection.

Instead, Viagra helps support your body's natural response when you're in the mood, making it easier to get and keep an erection. In this guide, we’ll break down the science behind Viagra, explain how it works, and give you some practical advice on how to take Viagra.

Viagra works by helping blood vessels in your penis relax and widen to allow more blood to flow in and create an erection when you're sexually aroused. It does this by blocking an enzyme that normally breaks down erection-producing chemicals in your penis. Another benefit is that Viagra can help increase the pressure within the penis during an erection, making it harder for blood to flow out.

This can help you get a stronger and more reliable erection.

Getting an erection is a coordinated effort involving your brain, blood vessels, hormones, and nerves. 

Here’s the science behind it:

1. When you’re sexually aroused, your brain triggers the release of nitric oxide (NO) in the blood vessels of the penis.

2. Nitric oxide stimulates the production of a chemical called cyclic guanosine monophosphate (cGMP) in the smooth muscle cells of the penis.

3. This chemical relaxes the muscles in the penis, allowing more blood to flow into two sponge-like chambers called the corpora cavernosa.

4. This causes blood to get trapped in the penis, creating a natural erection.

5. After ejaculation takes place, the enzyme phosphodiesterase type 5 (PDE5) breaks down cGMP, causing the blood to flow back out and the erection to subside.

When this process doesn’t work as it should, it causes ED. Sometimes, PDE5 acts too soon, breaking down cGMP before enough blood has entered the penis. Without sufficient blood flow, an erection either won’t happen or won’t last.

Now, you might have also heard people comparing Viagra to sildenafil, so it’s worth going over how sildenafil works and whether it’s different from Viagra.

Viagra vs. sildenafil: are they different?

The answer is no; they aren’t different. Both Viagra and sildenafil treat ED and share the same active ingredient: sildenafil citrate. Viagra is simply the brand-name version, while sildenafil is the generic alternative.

Both medications belong to a group of drugs called PDE5 inhibitors, which relax the muscles in blood vessel walls to improve blood flow to the penis.

Both are available in 25 mg, 50 mg, and 100 mg doses (sildenafil is also available in 20 mg when prescribed as Revatio off-label for ED), with the specific dosage being something you’ll determine with your healthcare provider.

The main difference is cost—sildenafil is typically less expensive because it’s made by multiple manufacturers, while Pfizer owns and produces the brand name Viagra.

For most people, Viagra typically begins to work within 30 to 60 minutes after taking the pill. If you’re taking it for the first time, the makers of Viagra recommend planning to take it about an hour before sexual activity.

That said, the exact timing required for it to take effect can vary depending on factors like your metabolism, whether you’ve eaten recently, and whether you’re aroused.

Here’s a quick overview of what to expect:

• Quick onset for some: A study found that some men experienced effects within 12 minutes of taking Viagra.

• Average response time: Another study found that the median time it takes for people to get an erection is around 27 minutes after taking the medication.

• Peak effectiveness: Viagra typically reaches its highest concentration in your bloodstream at the 1-hour mark.

• Extended effectiveness window: The effects of Viagra can last up to 4 hours, though they gradually decrease over time.

Several factors influence how quickly Viagra works. A heavy, high-fat meal like burgers, fries, or pizza can slow down absorption—potentially delaying the medication's effects by up to an hour.

Alcohol consumption matters too––while a single glass of wine or beer typically won't cause issues, heavy drinking can reduce Viagra's effect.

If you’re taking Viagra as prescribed and still not seeing the results you want, your healthcare provider can help adjust your dosage or recommend alternative treatments that might work better for you.

Viagra can work for about 4 hours after you take it, but the exact timing can vary from person to person. 

That’s why it’s a good idea to take it around an hour before you plan to have sex. If things don’t go exactly according to schedule, you won’t need to worry—Viagra could still work as long as you’re within that 4-hour window.

For those wondering how long Viagra is in your system, the answer is that it depends. 

How long Viagra lasts depends on a few factors, such as:

• Your age: As you get older, your body might process the medication more slowly. But, Viagra has generally been found to be safe, even for those who are older.

• The dose you take: Higher doses may stick around a little longer.

• Other medications or health conditions: These can affect how your body absorbs or breaks down Viagra.

• What you’ve eaten: A big, heavy meal can delay how quickly Viagra kicks in, though it won’t necessarily change how long it lasts.

While Viagra is active in your system, it’s possible to have more than one erection if you’re aroused again. But it’s important to know what’s normal and what’s not.

If your erection lasts longer than 4 hours, even if it doesn’t hurt, you should get medical help right away. This condition, called priapism, is uncommon but serious and needs treatment to avoid long-term problems.

The way Viagra works can vary, so it’s okay if it takes some time to figure out what feels right for you. If you’re unsure or have questions, talking to your healthcare provider can help you use Viagra safely and confidently.

Viagra is a prescription pill designed to help with ED, and taking it correctly is essential to getting good results. It’s typically prescribed to be taken as needed, not daily, so you’ll need to plan ahead before sexual activity.

• Timing it: Plan to take Viagra about 30 minutes to 1 hour before sex. It takes time to absorb and start working, so don’t wait until the last minute. The effects can last up to 4 hours, giving you a flexible window to engage in sexual activity.

• Swallow it with water: Viagra is meant to be taken whole—don’t chew, crush, or attempt other creative methods like snorting it (yes, people have tried).

• Follow your healthcare provider’s instructions: Doses typically range from 25 mg to 100 mg, depending on what works best for you. Start with the dose prescribed by your provider, and never exceed one dose per day.

• Take it on an empty stomach if possible: Viagra can work whether you’ve eaten or not, but a heavy, fatty meal may delay how quickly it kicks in. If you’ve recently eaten a very large meal, then waiting a couple of hours before taking it can increase its effectiveness.

• Be patient: Viagra doesn’t always work perfectly the first time, especially if factors like food, alcohol, or stress come into play. If it doesn’t seem effective, talk to your healthcare provider about potential adjustments.

Remember that Viagra requires sexual arousal to work. It doesn’t cause an erection on its own but supports your body’s natural response to stimulation.

Viagra can be an effective tool for managing ED, but getting the best results often involves more than just taking the pill. Here are practical ways to optimize your experience:

• Be mindful of alcohol consumption. Moderate drinking—one or two standard drinks weekly—is usually fine, but heavy drinking (8 or more drinks per week for women or 15 or more for men) can make it harder for Viagra to work effectively. Alcohol can also cause blood pressure to drop, leading to dizziness or lightheadedness.

• Be patient with your body. ED can be a stressful experience. And if it’s your first time using Viagra, it might not deliver immediate results exactly as you’d hoped. It can take a few tries to figure out how your body responds and optimize dose and timing

• Set your expectations right. Viagra can improve your natural ability to have an erection, but it doesn’t give you superhuman stamina or guarantee multiple rounds. Listen to your body, and don’t overdo it—trying to push beyond what feels natural could leave you feeling frustrated.

• Communicate with your partner. Open communication can help ease performance anxiety and create an environment where you feel comfortable. Your partner’s involvement and understanding can play a big role in how satisfying the experience feels.

• Other health considerations: Viagra is generally safe to take, but if you’ve had a heart condition like high or low blood pressure or heart disease, you should let your healthcare provider know so they can take that into account when planning your treatment. Be sure that you are cleared for sexual activity before taking medication as those with recent surgery or heart conditions may not be cleared by their healthcare providers

Like any FDA-approved medication, Viagra can come with some side effects. While most are mild and temporary, it’s important to understand what to expect and when to get help.

Common side effects

Mild side effects of Viagra often go away within a few hours and include:

• Headaches

• Flushing

• Indigestion or upset stomach

• Stuffy nose 

• Changes in vision (e.g., sensitivity to light or altered color perception)

These side effects are usually more likely with higher doses. Since these effects can vary from one person to the next, it’s important to try different options and figure out the one that works best for you by discussing it with your healthcare provider. 

Rare side effects

Some less frequent but possible side effects include:

• Chest pain

• Shortness of breath

• Low blood pressure

• Fainting

Viagra itself can lower blood pressure, so if you already have low blood pressure or take medication for high blood pressure, you should discuss this with your healthcare provider before using Viagra.

In rare cases, Viagra can cause:

• Priapism: A painful erection that doesn’t go away. If your erection lasts longer than four hours, seek medical attention immediately to avoid permanent damage to the penis.

• Sudden vision or hearing loss: If you experience sudden changes in your ability to see or hear, it’s crucial to get medical help right away.

By understanding how Viagra works, you can use it safely and effectively while minimizing potential risks. If you have any concerns or questions, don’t hesitate to discuss them with your healthcare provider.

Taking Viagra without considering certain health conditions or medications can lead to serious complications. That’s why it’s essential to have a conversation with your healthcare provider before starting Viagra.

If you have any of the following, it’s crucial to let your healthcare provider know:

• Heart problems: This includes high blood pressure, a recent heart attack, or other forms of heart disease.

• Blood disorders: Conditions like sickle cell anemia can increase your risk of complications, such as priapism (a prolonged and painful erection).

• Peyronie’s disease: A condition that causes abnormal curvature of the penis and may complicate erections.

• Kidney or liver issues: These can affect how your body processes Viagra, potentially leading to higher levels of the medication in your system.

Your healthcare provider can assess whether Viagra is a safe option based on your overall health and medical history.

Drug interactions with Viagra

Viagra can interact with certain medications, so be sure to provide your provider with a full list of everything you’re taking.

Key medications to be aware of include:

• Nitrates: Commonly prescribed for chest pain, nitrates (like nitroglycerin) increase nitric oxide levels to relax blood vessels. Combined with Viagra, this can cause a drop in blood pressure.

• Alpha-blockers: Used for conditions like high blood pressure or prostate issues, these can also lead to dangerously low blood pressure when taken with Viagra.

• Guanylate cyclase stimulators: Often used to treat certain lung conditions, these may not be safe to combine with ED medications.

• Antifungals and other medications: Some drugs that treat fungal infections can interfere with how Viagra is processed in the body.

• Recreational drugs: Substances like "poppers" (amyl nitrite) should never be mixed with Viagra, as they also affect blood vessel relaxation and can lead to serious complications.

Remember that this list is by no means exhaustive––you should share all the medications you are taking with your healthcare provider.

If Viagra isn’t a suitable option for you, there are several other effective treatments for ED that you could ask your healthcare provider about. 

From longer-lasting options to chewable alternatives, here’s a breakdown of what’s available:

Cialis (Tadalafil)

Cialis is a PDE5 inhibitor like Viagra, but can offer a longer duration of action, with effects lasting up to 36 hours. This makes it an excellent choice for those who value spontaneity or don’t want to worry about planning sex around their medication.

For even more convenience, Cialis is available in a daily low-dose formulation. By taking a smaller dose every day, you can maintain a steady level of the medication in your system, allowing you to be ready for sex whenever the moment feels right.

Stendra (Avanafil)

If you’re looking for something that can work fast, avanafil can typically start working within 15 minutes and can provide effects for about 4 to 6 hours.

Its quick onset makes it a good choice for those who prefer minimal waiting time between taking the medication and engaging in sexual activity.

Vardenafil

Vardenafil offers effects similar to Viagra, and can last around 4 to 5 hours, but with a slightly faster onset of action (usually within 15 to 60 minutes). It’s a solid alternative for those who want a dependable, fast-acting medication that doesn’t require as much advance planning.

Daily Rise Gummies

For those who don’t like pills or want a consistent, low-maintenance option, Daily Rise Gummies can provide a flavorful and convenient way to manage ED. Each gummy contains 7 mg of tadalafil, the same active ingredient as Cialis, and is designed for daily use.

By taking these gummies every day, you can build a steady level of tadalafil in your system, which could allow you to get an erection whenever you’d like to have sex.

It’s ideal for those who prefer spontaneity and a pill-free alternative.

Ro Sparks

Ro Sparks combines the fast-acting benefits of sildenafil (Viagra) with the long-lasting effects of tadalafil (Cialis) in a single dissolvable tablet. Each tablet contains 55 mg of sildenafil and 22 mg of tadalafil, which can deliver both immediate and extended results.

The medication can typically start working within 15 minutes, and its effects can last up to 36 hours, making it a great choice for those looking for the benefits of sildenafil and tadalafil combined.

While this formulation is not FDA-approved, it is composed of active ingredients that are FDA-approved for ED.

Recognizing what Viagra can do—and what it can’t—can help you use it effectively and manage your expectations.

Viagra is prescribed to treat ED. It doesn’t work automatically or create physical changes beyond its intended purpose. The medication won’t create arousal on its own—Viagra can only improve your body’s ability to respond to sexual stimulation. It also won’t solve issues like low libido or emotional barriers to intimacy, which often require a different approach to treatment.

Does Viagra make you last longer?

While Viagra primarily addresses ED and isn’t designed to make you last longer, it may have an indirect effect on how long you last in bed for some people––mainly by helping you feel more confident.

However, there’s often a connection between erectile dysfunction and premature ejaculation, and addressing one issue can sometimes help with the other.

If Viagra helps you maintain a firm erection and boosts your confidence, you may find that it has a positive, indirect effect on how long you last.

But if lasting longer during sex remains a concern, your healthcare provider might recommend other strategies, like behavioral techniques, therapy, or even medications such as numbing creams or antidepressants that can address premature ejaculation.

Ro offers a range of options that can help with PE, including Roman Swipes, which are benzocaine wipes that can help you last up to four times longer, and sertraline, a daily prescription medication that can help delay ejaculation which can be prescribed if you qualify

Does Viagra make your penis bigger?

It’s a common question––”How many inches does Viagra give you?” Viagra doesn’t increase the size of your penis. It can improve blood flow, which can help you get a firmer, fuller erection. While this may make your penis feel larger than when it is flaccid, the medication doesn’t actually change the physical dimensions of your penis.

It’s natural to have questions about size, especially if you’ve struggled with ED. But the primary goal of Viagra is to help you achieve and maintain an erection that allows you to enjoy sex, not to alter the size of your penis.

Does Viagra make you hornier?

Viagra can’t directly increase your sex drive or make you feel aroused. It can help your body respond to sexual stimulation by increasing blood flow to the penis. But, many people find that successfully treating ED improves their sexual confidence, which can naturally boost their interest in sex.

What do you do if Viagra isn’t working?

If Viagra doesn’t seem to be working for you, there are a few steps you can take.

• Try it again another time: It can take a few attempts to see how your body responds. Many providers recommend trying Viagra a few times before deciding it’s not right for you.

• Check your dose timing: Take Viagra 30 minutes to 1 hour before sexual activity. If you wait too long or take it too early, it may not work as well.

• Take it on an emptier stomach: Eating a heavy or high-fat meal before taking Viagra can delay how quickly it works. You could try taking it on an empty go by or light stomach to see if you get a better result. Always prioritize your safety - we don’t advise fasting but you could try to limit fatty meals. 

• Minimize alcohol: Excessive alcohol can interfere with the medication’s effectiveness and make it harder to get an erection.

• Make sure you’re sexually stimulated: Viagra doesn’t cause arousal—it can only enhance your body’s natural response to arousal by helping you get an erection. Sexual stimulation is necessary for it to work.

• Talk to your healthcare provider: If you’ve tried all of these things and still don’t see results, your provider may adjust your dosage or recommend alternative treatments.

Do you need a prescription for Viagra?

Yes, Viagra requires a prescription. This ensures that you’re using the medication safely and that it’s the right treatment for your specific needs. Viagra’s active ingredient, sildenafil, is also available in generic forms, which are considered just as effective and safe as the brand-name version.

Generic sildenafil works in the same way as Viagra but typically costs less, making it a more affordable option for many people. If you’re interested in trying a generic form, your healthcare provider can help you determine if it’s available in the appropriate form and dosage for you.

Where do you get a prescription for Viagra?

Getting a prescription for Viagra doesn’t have to be complicated or uncomfortable. You have several options, whether you prefer to visit a healthcare provider in person or take advantage of online services:

Visit your primary care provider

Talking to your primary care provider can be a great starting point if you’re experiencing ED. They’re familiar with your overall health history and can evaluate your symptoms to determine if Viagra is a safe and effective option.

During your visit, they’ll likely:

• Ask about your ED symptoms, such as difficulty getting or maintaining an erection.

• Review your medical history, medications, and lifestyle to identify any underlying causes, such as heart disease, diabetes, or stress.

• Discuss the potential risks and benefits of Viagra or other ED treatments.

If Viagra is right for you, they’ll write a prescription. If not, they may recommend alternative treatments, including other medications, lifestyle changes, or therapies.

Consult a urologist

If you’d rather see a specialist, a urologist is an excellent option. Urologists specialize in conditions affecting the urinary tract and reproductive system––they’ve got plenty of experience when it comes to managing ED.

The advantage with a urologist is that they can provide a more in-depth evaluation of underlying causes, such as hormonal imbalances or physical conditions like Peyronie’s disease, and offer advanced treatment options that go beyond oral medications, if they’re required.

Try an online medical consultation

If you prefer to skip in-person visits, online healthcare services make it easier than ever to get a prescription for Viagra. With an online consultation, you can:

• Complete a health questionnaire about your symptoms, medical history, and any current medications.

• Speak with a licensed healthcare provider via video or chat from the comfort of your home.

• Receive a prescription if Viagra is deemed appropriate and have it shipped to your door.

This option is convenient, saves time, and eliminates the potential awkwardness of face-to-face conversations. Many online platforms also offer generic sildenafil, which can be significantly more affordable than brand-name Viagra.

Ro connects you with licensed healthcare providers who can evaluate your needs and prescribe Viagra or a generic alternative if it’s right for you. The process is straightforward:

• Complete an online health assessment: Fill out a secure questionnaire about your medical history, ED symptoms, and current medications.

• Provider review: A licensed healthcare provider reviews your information, asks follow-up questions if necessary, and determines the appropriate treatment.

• Discreet delivery: If prescribed, the medication is shipped directly to your door in discreet packaging.

• Ongoing support: Ro offers unlimited follow-ups, allowing you to adjust your treatment or ask questions as needed.

Viagra works by improving blood flow to the penis, which can help people with ED get and maintain an erection during sex.

It does this by blocking the PDE5 enzyme, which allows blood vessels to relax and more blood to flow into the penis when you’re sexually aroused. But, it requires sexual stimulation to be effective and doesn’t increase libido or change the size of your penis.

If Viagra isn’t working for you, your healthcare provider can recommend other options like Ro Sparks or Daily Rise Gummies, which can offer more flexible ways to address ED. Whether you choose Viagra or another treatment, the key is finding an option that aligns with your needs and lifestyle. Consult a healthcare provider to explore your options and take the first step toward more confident and satisfying sex.

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How we reviewed this article

Every article on Health Guide goes through rigorous fact-checking by our team of medical reviewers. Our reviewers are trained medical professionals who ensure each article contains the most up-to-date information, and that medical details have been correctly interpreted by the writer.

Editorial Guidelines | Medical Review Process

Current version

December 13, 2024

Written by

Sonia Rebecca Menezes

Fact checked by

Raagini Yedidi, MD

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About the medical reviewer

Raagini Yedidi, MD

Raagini Yedidi, MD, is an internal medicine resident and medical reviewer for Ro.