Medically reviewed by Jill Johnson, FNP
Written by Our Editorial Team
Last updated 11/17/2022
Sildenafil is a rockstar pill when it comes to managing erectile dysfunction (ED), and it isn’t just because it was the very first on the scene.
Approved for use back in 1998, this medication — otherwise known as the active ingredient in Viagra® — is one of the first names you’re likely to come across if you’re one of the millions of adult men who either live with erectile dysfunction or suspect you may have it.
Like other medications, sildenafil comes in several doses, ranging from as little as 25mg a tablet to as much as 100mg. The dosage you’ll be prescribed by your healthcare provider will likely be tailored to your needs based on the severity of your erectile dysfunction symptoms.
Is it okay to take 100mg of sildenafil? As the highest dose of sildenafil, taking 100mg is alright if you’ve been prescribed this dose of sildenafil by your healthcare provider. However, your risk of adverse effects is slightly higher with this dose than with sildenafil 25mg or 50mg.
Below, we’ve explained what sildenafil is, as well as how it functions for the treatment of erectile dysfunction.
We’ve also discussed what you should know about using oral sildenafil at a dosage of 100mg to treat ED, from common side effects you should be aware of to how you can take this medication for optimal results.
Before we discuss different doses of sildenafil, let’s cover the basics of how oral sildenafil works as a treatment for erectile dysfunction.
Sildenafil belongs to a class of prescription drugs called phosphodiesterase type 5 inhibitors, or PDE5 inhibitors. These medications work by expanding the blood vessels that transport blood to your penis.
Healthy, regular erections are all about blood flow. In response to sexual stimulation, blood flows into the tissue in your penis and becomes trapped in chambers within it This causes your penis to expand and allows it to stay hard, ensuring you’re saddled up for sexual intercourse.
Several factors come into play during this process, and the activities of a cyclic nucleotide called cyclic guanosine monophosphate (cGMP) are especially important.
This enzyme is responsible for relaxing the smooth muscles inside your blood vessels, allowing blood to flow to your penis and other parts of your body. PDE-5 breaks down cGMP in the blood, making it easier for you to develop and maintain an erection.
In other words, sildenafil and similar ED medications make having sex easier by supplying your penis with the blood it needs to get and stay hard.
One important feature of PDE5 inhibitors is that they only cause erections when you’re feeling in the mood for sex. Contrary to popular belief, they won’t cause spontaneous erections (assuming you aren’t thinking about something sexual) or affect your sex drive in any significant way.
This means that if you aren’t sexually aroused, you don’t need to worry about sildenafil causing an involuntary erection.
If you have erectile dysfunction and want to treat it, erectile dysfunction medication like sildenafil can offer numerous benefits.
Sildenafil starts working quickly — typically in one hour or less. When it’s taken as prescribed, it can provide relief from erectile dysfunction that lasts for approximately four hours. Better yet, it’s available as a single pill that you can use as needed before you plan to have sex.
Currently, 100mg is the highest dose of sildenafil that’s approved by the FDA for treating erectile dysfunction.
If you have mild or moderate ED, your healthcare provider will likely prescribe 50mg of sildenafil as your starting dose. This is the typical go-to oral dose for sildenafil, and it’s typically enough to treat erectile dysfunction and improve sexual performance for most men.
In some cases, this dosage may be reduced to 25mg of sildenafil if you’re prone to side effects, or if your healthcare provider thinks that a dosage of 50mg isn’t necessary.
Normally, you’ll only be prescribed sildenafil at a dosage of 100mg if you still find it difficult to get or maintain an erection after using a lower dose of sildenafil.
Your healthcare provider may also start treatment for erectile dysfunction with this dosage if you have severe symptoms. For example, if you can’t develop an erection at all, even following large amounts of sexual stimulation, you may start treatment with a single dose of 100mg sildenafil.
Your healthcare provider may also consider how often you have sex. For example, your dosage may be adjusted if you have sex frequently and take sildenafil every day, or if you only take this medication once every few days for less frequent sexual intercourse.
In short, your healthcare provider will select the right dosage of sildenafil for you based on your erectile dysfunction symptoms, as well as your personal needs.
Sildenafil has an impressive reputation for managing erectile dysfunction, so it’s no surprise that at its strongest dose, this delivers for the overwhelming majority of men.
In clinical trials, researchers found that 82 percent of men with ED reported some improvements in erectile function after using sildenafil at a dosage of 100mg.
The same trials found that 74 percent and 63 percent of men reported improvements with 50mg and 25mg of sildenafil, respectively.
Put simply, sildenafil works well for most men with erectile dysfunction at any dosage, although the highest 100mg dosage produces improvements for a greater percentage of men than 50mg or 25mg.
In a separate study conducted to determine how well men would respond to having their dosage of sildenafil increased, participants with ED were given a starting dose of 50mg, which was later increased to 100mg.
After taking sildenafil at a dosage of 50mg for two weeks, the men took 100mg of sildenafil prior to sex.
Participants found that they quickly experienced improvements in the feel of their erections, and were able to have more satisfactory sexual intercourse using the highest dose of sildenafil when compared with the starting dose of 50mg.
A similar study supported these findings. After four weeks of receiving sildenafil at 50mg, some participants with erectile dysfunction had their dosage increased to 100mg for the following four weeks.
While study participants showed some improvement on the initial dose of sildenafil, the quality of their erections and general level of sexual satisfaction went up more significantly after using 100mg of sildenafil.
Similarly, participants in a study that lasted over four years found that when using 25mg, 50mg, and 100mg of sildenafil as needed to manage ED, they had the most significant improvements with the 100mg dose.
Some men in the study experienced side effects of sildenafil, such as flushing and palpitations, yet issues were minimal overall.
Both brand name Viagra and its generic version sildenafil are safe and effective medications for most men. However, like with almost all medications, they do have the potential to cause certain adverse effects and drug interactions.
Most side effects of sildenafil are mild in nature, and it’s uncommon for them to persist for longer than the medication is active within your body. However, in rare cases, sildenafil treatment could also cause more severe or bothersome side effects.
Common side effects of sildenafil include:
Vision changes (blurred vision or changes in color perception)
Myalgia (muscle pain)
Many of these side effects occur more frequently with a 100mg dose of sildenafil than when this medication is taken at a dosage of 25 or 50mg.
For example, in clinical trials of sildenafil, 28 percent of men reported headache (by far the most common side effect) at a dosage of 100mg, compared to just 16 percent of men who used 25mg of sildenafil.
Although rare, sildenafil can also cause more severe side effects, including some that may need medical attention. These include chest pain, fainting, shortness of breath, sudden severe loss of vision and/or hearing, or an itching or burning sensation during urination.
In very rare cases, sildenafil may also cause priapism — a painful erection that may last for four hours or longer. Priapism is a serious emergency, and it’s important to get emergency medical attention as soon as you can avoid damaging the erectile tissue inside your penis.
Sildenafil and other PDE-5 inhibitor medications can interact with other drugs, including several common medications used to treat chest pain, high blood pressure and other conditions related to heart health and cardiovascular disease.
In particular, sildenafil can interact with nitrates and alpha-blockers, potentially causing a severe drop in systolic and diastolic blood pressure that could lead to fainting or serious cardiovascular events such as myocardial infarction (heart attack) or stroke.
As such, you should not take sildenafil or brand name Viagra if you use nitroglycerin or similar prescription organic nitrates, or if you use recreational drugs that contain nitrates such as amyl nitrate, amyl nitrite or butyl nitrate “poppers.”
In general, it’s best to inform your healthcare provider about any medications you currently take or have recently taken before you consider using sildenafil or a similar PDE5 inhibitor for ED.
It’s also important to tell your healthcare provider if you have any underlying medical conditions, particularly heart disease, sickle cell anemia, pulmonary hypertension, an irregular heartbeat, or if you have previously experienced any type of cardiovascular event.
The more you can tell your healthcare provider, the better they’ll be able to assess your risk and make sure you’re safe while using sildenafil.
One of the biggest advantages of sildenafil is that it’s an easy medication to use. For the most part, sildenafil can be taken before sex without any major concerns. However, there are a few things that you can do to get the best results from this medication. Try to:
Take sildenafil 100mg around one hour before sex. Sildenafil usually takes about one hour to start working. For optimal results, take your prescribed dose of sildenafil an hour before the time you plan to have sex.
Avoid high-fat meals while using sildenafil. Eating a meal high in fat may slow down your body’s absorption of sildenafil and delay its effects. Try to eat a normal meal with a low to moderate fat content to ensure sildenafil works as expected.
Don’t panic if sildenafil isn’t effective the first time. A variety of factors can all play a role in erectile dysfunction, and sexual performance anxiety is one of them. If you start to feel nervous before sex, medication like sildenafil may not be totally effective.
If sildenafil doesn’t work the first time you use it, don’t panic. Instead, continue to use it before you have sex and tell your healthcare provider if you don’t notice improvements over time.
Be wary of herbal products for ED. Certain herbal remedies for ED contain hidden or dangerous ingredients that shouldn’t be used with sildenafil. It’s best to avoid using any of these products, as they may increase your risk of drug interactions.
Combine sildenafil with healthy habits. Simple habits such as exercising often, eating a balanced diet and limiting your alcohol intake can all have a positive effect on erections and sexual performance.
In addition to using sildenafil, try to have a healthy lifestyle. Our guide to maintaining an erection naturally shares 14 techniques that you can use to reduce your risk of ED and enjoy better sex.
Sildenafil comes in several dosage forms. Your healthcare provider may prescribe sildenafil at a dosage of 100mg if you have moderate to severe erectile dysfunction, or if you don’t experience any improvements at a lower dosage.
Sildenafil is most effective as an ED treatment when it’s taken at this dosage, but it also has the highest risk of causing side effects. As such, it’s important to let your healthcare provider know if you experience any issues while using sildenafil to treat ED.
If you do experience adverse effects with sildenafil, you may benefit from using a more selective inhibitor of PDE5, such as avanafil (available as Stendra®).
Interested in finding out more before you get started? Our guide to the most common treatments for erectile dysfunction goes into more detail about your most effective options, from sildenafil to several other FDA-approved medications for treating ED and having more satisfying sex.