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Viagra FAQs: 22 Common Questions About Viagra Answered

Kristin Hall, FNP

Medically reviewed by Kristin Hall, FNP

Written by Our Editorial Team

Last updated 1/21/2022

Got a question about Viagra®? We’ve got answers. From the history of the drug to information about Viagra’s onset of action, potential side effects and more, we’ve answered 22 of the most common questions about Viagra (as well as its generic drug counterpart, sildenafil) below.

What is Viagra?

Viagra is the brand name of a popular ED medication. Viagra tablets contain sildenafil, a PDE5 inhibitor that works by blocking the effects of phosphodiesterase-5, an enzyme that controls the flow of blood to the erectile tissue inside your penis.

You can purchase Viagra as a brand name medication manufactured and marketed by Pfizer, or as sildenafil (generic Viagra). 

Viagra comes in tablet form and is taken before sex. It’s a prescription medication, meaning you will need to talk to your healthcare provider and receive a prescription before you can purchase and use it.

When Was Viagra Invented?

Sildenafil, the active ingredient in Viagra, was originally developed in the 1980s as a treatment for angina (chest pain caused by reduced blood flow to the heart) and hypertension (high blood pressure).

During drug testing, Pfizer discovered that the medication was more effective at treating erectile dysfunction than angina and decided to market it for this purpose.

After undergoing clinical testing throughout the 1990s, Viagra was approved by the FDA in 1998 and soon went onto the market as the first oral treatment for erectile dysfunction.

Viagra has now been in use for more than 20 years, making it the oldest FDA-approved erectile dysfunction treatment on the market.

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How Does Viagra Work to Treat ED?

Viagra belongs to a class of drugs called PDE5 inhibitors. These medications work by blocking the degradative action of the PDE5 enzyme (cGMP-specific phosphodiesterase type 5).

PDE5 plays an important role in regulating blood flow to the soft, sponge-like tissue that’s inside your penis, called the corpora cavernosa.

When you’re sexually aroused, blood flows into this tissue, causing your penis to become firmer and larger. A membrane called the tunica albuginea traps this blood inside your penis, allowing you to have sex with your partner.

After you reach orgasm and ejaculate, the muscles inside your penis contract, allowing blood to flow out from your penis.

In simple terms, Viagra (as well as other erectile dysfunction drugs, such as Cialis and Levitra) works by improving blood flow to the tissue of your penis. Our guide to how Viagra works goes into more detail about this process. 

Does Viagra Always Work?

Erectile dysfunction can occur for a variety of reasons, including physical health issues that can affect blood flow and psychological issues, such as sexual performance anxiety and depression, that may affect your level of interest in sex or comfort in the bedroom.

Viagra works by increasing blood flow into the soft tissue of your penis. It’s very effective at this, making it a great treatment option if you have erectile dysfunction caused by a health issue that affects blood flow throughout your body. 

However, Viagra does not directly affect the psychological side of sexual performance, such as your level of interest in sex, arousal level or sexual confidence. 

This means that if your ED is caused by a psychological issue, Viagra or other ED medications may not be fully effective. 

Not everyone who uses Viagra experiences improvements in erectile function. In clinical trials, the success rate of Viagra (percentage of men who reported improved erections) ranged from 66 to more than 80 percent.

Some medical conditions, such as diabetes, may reduce the effectiveness of Viagra and other ED medications.

Viagra might also be less effective if you’ve undergone a surgical procedure that affects your sexual function, such as a radical prostatectomy.

Our guide to what you can do if Viagra doesn’t work discusses this issue in greater detail and explains how you can overcome common causes of ED.

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What Other Health Conditions is Viagra Used For?

Currently, the brand name drug Viagra is only made and prescribed as a treatment for erectile dysfunction. 

However, sildenafil, the active ingredient in Viagra, is also used as a treatment for conditions such as pulmonary arterial hypertension (PAH), a form of high blood pressure that affects the blood vessels in the lungs.

When sildenafil is used to treat PAH, it’s often marketed under the name Revatio® and uses a reduced dosage of sildenafil.

When Should You Consider Using Viagra?

Viagra can be a safe and effective erectile dysfunction treatment for men of all ages. Contrary to popular belief, it’s not used exclusively by older men. 

There’s no ideal age for using Viagra or other ED medication. In general, you should think about using Viagra if you:

  • Find it difficult or impossible to get an erection at any time

  • Can get an erection, but find it difficult to maintain it during sex

  • Can’t get an erection every time you want to have sex

Viagra can be used every time you have sex, or occasionally if you feel worried about the risk of erectile dysfunction. 

You may want to consider using Viagra if you have one or several of the common risk factors for erectile dysfunction

How Long Does it Take for Viagra to Work?

Sildenafil, the active ingredient in Viagra, usually starts to work approximately 30 minutes after you take it. For optimal results, Viagra or generic sildenafil should be taken about one hour in advance of sex.

It may take longer for Viagra to start working if you’ve eaten a large meal, particularly if the meal has a high fat content. 

How Do I Take Viagra for the Best Results?

For best results, you should take Viagra on a relatively empty stomach around one hour before you expect to have sex. A normal dose of Viagra should remain effective for approximately four hours. 

Avoid drinking large amounts of alcohol while using Viagra or generic sildenafil. If you use other medications, check with your healthcare provider to make sure they do not interact with Viagra, reduce its effectiveness or have any other safety risks. 

Viagra and generic sildenafil come in several doses, from 25mg to 100mg. You may need to try several different doses of sildenafil before finding one that’s most effective for you.

Follow your healthcare provider’s instructions while using this medication.

Can Any Factors Affect How Long Viagra Lasts?

Yes. Several different factors can affect how long Viagra remains active in your body, as well as its effectiveness as an ED treatment. These include:

  • Your Viagra dosage. Like other medications, a normal dose of Viagra slowly becomes less effective as it leaves your body. A larger dose may remain active for slightly longer than a smaller dose.

  • Your recent eating habits. Some types of food, particularly fatty food, may slow down your body’s absorption of Viagra. Eating a high-fat meal before using Viagra may affect how long it takes to work and increase the amount of time that Viagra is active.

  • Your use of medication. Some medications, including certain antibiotics, antiretrovirals and antifungal medications, may increase the effects of Viagra and affect the amount of time required for your body to process the medication.

  • Your psychological wellbeing. Viagra may be less effective, or last for a shorter period of time, if you have sexual performance anxiety, depression, feelings of guilt about sex or other mental health issues that affect your sexual function.

  • Your physical health. Some physical conditions, such as heart disease and/or diabetes, may reduce the effectiveness of Viagra or cause it to provide relief from ED for a shorter period of time.

One additional factor that can affect how long Viagra lasts is your age. In general, older men are more likely to experience increased concentrations of certain medications, as well as a reduced level of effectiveness. This may affect Viagra’s effects or duration of action. 

Is it Possible to Make Viagra Work Faster?

When you swallow an oral medication such as Viagra, the medication is absorbed through your gastrointestinal tract.

This process requires time, and there’s nothing that you can do to speed it up once the medication is already inside your body.

However, you can make Viagra work faster by taking it under the right conditions. For the fastest effects, take Viagra on an empty stomach and avoid eating any food for approximately one hour after you take the medication. 

Doing this limits the workload of your digestive system, allowing the sildenafil in the Viagra tablet to be absorbed as rapidly as possible. 

What is a Normal Dose of Viagra?

Viagra, whether from Pfizer or as sildenafil, is available in several different doses. The smallest dose of Viagra is 25mg (generic sildenafil is also available in a 20mg dose), while the maximum dose of Viagra contains 100mg of sildenafil.

Depending on your needs and the severity of your ED symptoms, you may be instructed to use Viagra at a prescribed dose of 25mg, 50mg or 100mg by your healthcare provider.

Clinical trials show that most men with erectile dysfunction experience improvements from 50mg of Viagra taken before sex. 

If you have severe or persistent ED, your healthcare provider may increase your Viagra dosage to 100mg. On the other hand, if you develop side effects from Viagra or only have mild ED, you may be prescribed Viagra at the lower 25mg dosage. 

Our Viagra dosage guide goes into more detail about the available dosages of Viagra and their potential effects. 

What’s the Difference Between Viagra and Sildenafil?

Viagra and sildenafil are the same thing. Viagra is a brand name for the ED original medication developed and marketed by Pfizer, while sildenafil is the active ingredient inside the tablet that treats ED.

One tablet of Viagra contains either 25mg, 50mg or 100mg of sildenafil.

Generic sildenafil has all of the same effects and side effects of Viagra. The only real difference is that it’s sold under a different name (and is often much more affordable). 

When you take generic sildenafil, you’ll experience the same improvements in erection quality and sexual performance as you would from brand name Viagra, as well as the same potential side effects. 

What Are the Side Effects of Viagra?

Viagra is a safe, effective medication that most men can take without major issues. Like other medications, it can sometimes cause adverse effects. Most side effects of Viagra are mild and transient, while some can be more serious.

The most common side effects of Viagra are headaches, facial flushing, dyspepsia (indigestion), changes to your vision, nasal congestion, back pain, muscle pain, nausea, dizziness and rash.

Many of these side effects also often occur with other prescription medications for ED, such as tadalafil (the active ingredient in Cialis®), vardenafil (Levitra®) and avanafil (Stendra®).

In rare cases, Viagra and generic sildenafil may cause more serious side effects and/or allergic reactions, including chest pain, fainting, shortness of breath, loss of vision and priapism (a type of prolonged erection that may be painful).

If you experience any of these symptoms it is important to call 911 or get immediate medical attention.

How Long Does Viagra Stay in Your System?

The effects of Viagra typically last for three to four hours, after which the medication stops being effective at preventing erectile dysfunction.

Certain side effects of Viagra, such as nasal congestion, flushing and indigestion, may continue for several hours after the medication exits your system.

Although Viagra stops working after three to four hours, small amounts of sildenafil may remain in your bloodstream for one day or longer.

This means that you may not be able to safely use medications that can interact with sildenafil during this period.

Make sure to inform your healthcare provider about all medications you currently use before you use Viagra. 

How Often Can You Take Viagra?

Viagra is designed for use as needed, meaning you should take it around one hour before you plan to have sex.

Regardless of the exact dosage of Viagra you’re prescribed, you should not take this medication more than one time per day. 

If you want to have sex multiple times in one day and need a longer-lasting erectile dysfunction treatment, do not take more than one Viagra dose. 

Instead, it’s best to talk to your healthcare provider about potentially switching to a longer-lasting medication, such as tadalafil (sold as Cialis).

What Other Medications Work Like Viagra?

Viagra is one of several oral PDE5 inhibitors currently on the market as medications for erectile dysfunction. 

Similar medications include tadalafil (Cialis), vardenafil (Levitra) and avanafil (Stendra).

These medications work in the same way as Viagra, but have some key differences that may give one drug an advantage over others based on your needs.

Tadalafil is a long-lasting medication. Unlike the sildenafil in Viagra, which lasts for around four hours, a typical dose of tadalafil can provide relief from erectile dysfunction for approximately 36 hours.

Vardenafil, the ingredient in Levitra, lasts for a similar period of time to Viagra. Avanafil, a newer ED medication that’s sold as Stendra, is less likely to cause certain side effects and can work in as little as 15 minutes.

Our guide to the most common erectile dysfunction treatments and drugs lists the most common medications in this category and their effects. 

Are Natural Alternatives to Viagra Available?

There are countless supplements on the market that claim to provide similar results to Viagra, Cialis and other FDA-approved erectile dysfunction medications.

However, although many over-the-counter, natural ED supplements promise similar results to Viagra, few are reliable options for preventing ED. 

These supplements tend to contain ingredients such as “horny goat weed” (actually epimedium) that claim to boost testosterone and improve erections.

There’s no significant scientific evidence proving that these ingredients work as treatments for erectile dysfunction.

More concerningly, many of these “natural” male enhancement and ED supplements have been found to contain secret, unlisted ingredients such as powdered sildenafil.

The FDA maintains a list of tainted male enhancement supplements to warn consumers about these products. 

These supplements do not produce similar effects to Viagra, Cialis or Levitra and should not be viewed as reliable treatments for erectile dysfunction. 

Other supplements, such as certain vitamins and minerals, may help to improve erection quality and reduce the severity of erectile dysfunction.

However, these are much less effective than the FDA-approved medications and are rarely suitable for severe cases of ED.

Is it Possible to Treat ED Without Viagra?

In some cases, it’s possible to treat erectile dysfunction and improve your sexual performance without using medication like Viagra.

Erectile dysfunction can develop for a variety of reasons. Sometimes, lifestyle factors, such as excessive alcohol consumption, lack of physical activity, obesity, smoking or illicit drug use, can cause or contribute to ED.

If your ED is caused by an underlying health condition or habit such as obesity, tobacco use, low testosterone or a dietary issue, it might be possible to reduce the severity of your ED symptoms without the use of Viagra.

This might involve using a hormonal treatment, changing your use of other medications, losing weight or making changes to your lifestyle to improve your general health and reduce your risk of being continually affected by ED. 

When Will Generic Viagra Be Available?

Generic sildenafil (the active ingredient in Viagra) is already available in the United States, as well as in numerous other countries.

Using our online service, you can order generic sildenafil online, following a consultation with a healthcare provider who will determine if a prescription is appropriate. 

Generic sildenafil offers the same effects as brand name Viagra, but is typically available at a lower price. 

Other erectile dysfunction drugs, such as tadalafil (a generic form of Cialis) are also available online.

Is Viagra Available Over the Counter?

In the United States, Viagra is a prescription medication, meaning you’ll only be able to buy and use it with a prescription from your healthcare provider.

Currently, there are no ED medications approved by the FDA that are available over the counter.  

Subject to approval, you can buy sildenafil online after completing an online consultation with a licensed healthcare provider.

What Happens if a Woman Takes Viagra?

Since Viagra works by increasing blood flow to the soft erectile tissue of the penis, it’s not an effective medication for sexual dysfunction in women. 

According to the FDA label for Viagra, it’s currently not known if Viagra is safe or effective for women or children under the age of 18.

In general, the results of research on female Viagra usage are mixed, with few strong findings supportive of its use.

Women with sexual performance or desire issues should not use Viagra. Instead, it’s best to speak with your healthcare provider about treatment options.

From hormonal medication to newer sexual drugs such as Addyi® (flibanserin), there are now several similar medications for women with sexual dysfunction or sexual performance issues.

Does Viagra Expire?

Like most medications, Viagra can become less effective over time and expire if it’s left unused for too long.

Take note of the expiration date printed on your Viagra or generic sildenafil and aim to use the medication as prescribed before it expires. 

If your Viagra has expired, do not use it. Instead, dispose of the medication responsibly and purchase a new packet of Viagra or generic sildenafil.

Is it Safe to Use Viagra and Other ED Medications Together?

It is not recommended to take Viagra with other ED medications such as Cialis or Levitra.

Doing so may increase each medication’s effects, resulting in an increased risk of side effects such as headache, nausea and cardiovascular issues.

If you find that Viagra is not fully effective at treating your erectile dysfunction, do not combine it with other medications.

Instead, talk to your healthcare provider about adjusting your dosage of Viagra or using a longer-lasting erectile dysfunction medication such as Cialis. 

What if Viagra Doesn’t Work?

Viagra is highly effective at treating erectile dysfunction, with most men experiencing no issues achieving an erection after taking a 50mg or 100mg dose. However, it’s still possible for Viagra to fail in some situations.

While Viagra works well as a treatment for erectile dysfunction that’s caused by physical health issues, it does not treat a low sex drive or lack of arousal.

It also isn’t an effective treatment for mental health issues that can cause ED, such as anxiety or depression. 

If Viagra doesn’t work for you, your healthcare provider may adjust your dosage, switch you to a different type of medication or recommend a different type of treatment. 

Our guide to what you should do if Viagra doesn’t work covers this topic in more detail and lists other options for improving your sexual performance.

What Drugs Should Be Avoided While Using Viagra?

Viagra can interact with several widely-used medications, including many nitrates used to treat high blood pressure and some medications used to treat fungal infections. 

If you’re prescribed any type of nitrate or nitric oxide (NO) donor, you should not use Viagra.

If used together, these medications can cause a significant, sudden drop in blood pressure that may make you feel dizzy, faint or cause a heart attack or stroke.

Other medications used to treat high blood pressure and heart disease, such as alpha blockers, can interact with Viagra and cause issues such as fainting.

Other medications that should be avoided while using Viagra include oral antifungal or antibiotic medications, particularly ketoconazole, itraconazole, clarithromycin, erythromycin, telithromycin and others.

Some medications used to treat HIV, called HIV protease inhibitors, can potentially interact with Viagra and other ED medications.

Viagra should also not be used with other ED medications, such as tadalafil (Cialis), vardenafil (Levitra) and avanafil (Stendra).

Make sure to inform your healthcare provider about all prescription and over-the-counter drugs you currently use or have recently used before discussing Viagra. 

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Learn More About Treating Erectile Dysfunction

Erectile dysfunction is a most common forms of male sexual dysfunction, with approximately 30 million men affected in the United States alone. It can occur in men of all ages, including those in their 20s, 30s and 40s. 

If you’re one of the many men affected by erectile dysfunction, ED medications such as Viagra, Cialis and others can help you to improve your erections and restose your sexual function. 

We offer several ED medications, following an online consultation with a licensed provider who will determine if a prescription is appropriate. 

You can also learn more about the causes of ED and the most effective methods of treatment in our full guide to erectile dysfunction

12 Sources

Hims & Hers has strict sourcing guidelines to ensure our content is accurate and current. We rely on peer-reviewed studies, academic research institutions, and medical associations. We strive to use primary sources and refrain from using tertiary references.

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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.