Reviewed by Kristin Hall, FNP
Written by Our Editorial Team
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 citrate comes in several doses, ranging from as little as 20 mg 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.
Below, we’ve explained what sildenafil is, as well as how it functions for the treatment of erectile dysfunction. We’ve also discussed:
Whether 100 mg sildenafil is safe to take
How effective 100 mg sildenafil is
How long it takes to kick in
Side effects to watch out for
Let’s dive into how you can take this medication for optimal results.
Currently, 100mg is the highest dose of sildenafil that’s approved by the FDA for treating erectile dysfunction.
It is okay to take a 100mg dose of sildenafil, but normally, you'll only be prescribed this dosage if you still find it difficult to get or maintain an erection after using a lower dose of sildenafil.
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.
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. 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.
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.
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.
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.
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.
In a separate study, participants with ED were given a starting dose of 50mg, which was later increased to 100mg. Participants found that they quickly experienced improvements in the feel of their erections, and were able to have more satisfying 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.
Sildenafil at any dosage takes roughly 30 minutes to start working, but you should try to take it roughly an hour before sex. If that means slipping away into the bathroom after you’ve paid the bill or being sneaky on your way back to the car, you don’t want to take sildenafil 10 minutes before the clothes are coming off.
Sildenafil is a phosphodiesterase type 5 inhibitor, or PDE5 inhibitor. These medications work by inhibiting an enzyme and thereby expanding the blood vessels that transport blood to your penis.
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, sildenafil won’t “kick in” at all. Sad face.
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 it. Try to:
Take sildenafil 100mg around one hour before sex. Sildenafil usually takes about a half hour to start working, but 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 play a role in erectile dysfunction, and sexual performance anxiety is one of them. Continue to use it and tell your healthcare provider if you don’t notice improvements over time.
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.
Try to lead 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.
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Most side effects of sildenafil are mild in nature and it’s uncommon for them to persist for longer than the medication is active in your body. However, in rare cases, sildenafil treatment could also cause more severe or bothersome side effects.
Sildenafil side effects are generally mild and fade over time, but they occur more frequently at 100mg than 25mg and 50mg, respectively.
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 or 50mg of sildenafil.
Common side effects of sildenafil include:
Vision changes (blurred vision or changes in color perception)
Myalgia (muscle pain)
Although rare, sildenafil can also cause more serious side effects, including some that may need immediate medical attention. Severe side effects include:
Shortness of breath
Eye problems like blurred vision or sudden severe loss of vision (retinitis pigmentosa)
Sudden hearing loss
An itching or burning sensation during urination
In very rare cases, sildenafil may also cause priapism — a prolonged and 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 to 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 (sildenafil can cause low blood pressure) and other conditions related to heart health and cardiovascular disease.
Maybe this goes without saying, but if you want your blood flow to continue, do not double up on these medications. That includes over-the-counter gas station supplements that don’t have gov approval. Just leave them on the rack when you get your Big Gulp®.
In particular, sildenafil can interact with nitrates and alpha-blockers (like doxazosin), potentially causing a severe drop in systolic and diastolic blood pressure that could lead to fainting or serious cardiovascular events such as 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.”
Medications like ketoconazole, itraconazole and erythromycin will increase the effect of PDE5 medications as well. Weirdly, the same is true of grapefruit juice — it can affect the concentrations of medicine in your body, so you’ll most likely have to avoid it while taking this medication.
Seek medical advice from healthcare professional about any medications you currently take or have recently taken before taking sildenafil, and mention any underlying medical conditions, including:
Heart diseases like angina
Heart problems like pulmonary arterial hypertension or an irregular heartbeat
If you have previously experienced any type of cardiovascular event
A blood disease like leukemia or sickle cell anemia
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.
Sexual activity: the reason we’re all here, in more ways than one. If you’re not having the sex you want, sildenafil might be the pathway back.
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®) Others like tadalafil (Cialis) and vardenafil (Levitra) might be an option as well.
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.