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Sildenafil 100mg: How to Take It, Side Effects, and More

Mike Bohl, MD, MPH, ALM

Reviewed by Mike Bohl, MD, MPH, ALM

Written by Geoffrey C. Whittaker

Published 06/03/2021

Updated 01/10/2024

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 25 mg a tablet (20 mg when referring to the generic version of Revatio — a medication for a type of high blood pressure in the lungs) 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 and 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 it’s particularly difficult to get an erection, 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 very often, 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 to 60 minutes to start working, so 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. 

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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. 

Choose your chew

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 and 21 percent of men who used 50mg of sildenafil. 

Common Side Effects of Sildenafil 100mg

Common side effects of sildenafil include:

  • Headache

  • Flushing

  • Dyspepsia (indigestion)

  • Vision changes (blurred vision or changes in color perception)

  • Nasal congestion

  • Myalgia (muscle pain)

  • Back pain

  • Skin rash

  • Nausea

  • Dizziness

Rare Side Effects of Sildenafil 100mg

Although rare, sildenafil can also cause more serious side effects, including some that may need immediate medical attention. Severe side effects include: 

  • Eye problems like blurred vision or sudden severe loss of vision

  • Sudden hearing loss

In very rare cases, sildenafil may also cause priapism — a prolonged and painful erection that may last for four hours or longer. Priapism can be 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 100mg Drug Interactions

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 do not double up on these medications. That includes using with 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 called “poppers” that contain nitrites such as, amyl nitrite or butyl nitrite. 

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

  • Peyronie’s disease

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.

Sildenafil citrate

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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. 

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

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.

7 Sources

  1. (n.d) Label: Viagra (sildenafil citrate) tablets. Retrieved from:
  2. Ferguson, J. E., 3rd, & Carson, C. C., 3rd (2013). Phosphodiesterase type 5 inhibitors as a treatment for erectile dysfunction: Current information and new horizons. Arab journal of urology, 11(3), 222–229. Retrieved from:
  3. Eardley, I., Ellis, P., Boolell, M., & Wulff, M. (2002). Onset and duration of action of sildenafil for the treatment of erectile dysfunction. British journal of clinical pharmacology, 53 Suppl 1(Suppl 1), 61S–65S. Retrieved from:
  4. Saini, J. S., & Garg, M. K. (2001). VIAGRA : IS IT A WONDER DRUG ?. Medical journal, Armed Forces India, 57(1), 44–46. Retrieved from:
  5. Mulhall, J. P., Creanga, D. L., & Stecher, V. J. (2013). Improvement in erection hardness and intercourse success with first dose of sildenafil citrate 100 mg. International journal of general medicine, 6, 849–854. Retrieved from:
  6. Buvat, J., Hatzichristou, D., Maggi, M., Farmer, I., Martínez-Jabaloyas, J. M., Miller, P. J., & Schnetzler, G. (2008). Efficacy, tolerability and satisfaction with sildenafil citrate 100-mg titration compared with continued 50-mg dose treatment in men with erectile dysfunction. BJU international, 102(11), 1645–1650. Retrieved from:
  7. McMurray, J. G., Feldman, R. A., Auerbach, S. M., Deriesthal, H., Wilson, N., & Multicenter Study Group (2007). Long-term safety and effectiveness of sildenafil citrate in men with erectile dysfunction. Therapeutics and clinical risk management, 3(6), 975–981. Retrieved from:
Editorial Standards

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. See a mistake? Let us know at [email protected]!

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. Learn more about our editorial standards here.

Mike Bohl, MD, MPH, ALM

Dr. Mike Bohl is a licensed physician, a Medical Advisor at Hims & Hers, and the Director of Scientific & Medical Content at a stealth biotech startup, where he is involved in pharmaceutical drug development. Prior to joining Hims & Hers, Dr. Bohl spent several years working in digital health, focusing on patient education. He has also worked in medical journalism for The Dr. Oz Show (receiving recognition for contributions from the National Academy of Television Arts and Sciences when the show won Outstanding Informative Talk Show at the 2016–2017 Daytime Emmy® Awards) and at Sharecare. He is a Medical Expert Board Member at Eat This, Not That! and a Board Member at International Veterinary Outreach.

Dr. Bohl obtained his Bachelor of Arts and Doctor of Medicine from Brown University, his Master of Public Health from Columbia University, and his Master of Liberal Arts in Extension Studies—Journalism from Harvard University. He is currently pursuing a Master of Business Administration and Master of Science in Healthcare Leadership at Cornell University. Dr. Bohl trained in internal medicine with a focus on community health at NYU Langone Health.

Dr. Bohl is Certified in Public Health by the National Board of Public Health Examiners, Medical Writer Certified by the American Medical Writers Association, a certified Editor in the Life Sciences by the Board of Editors in the Life Sciences, a Certified Personal Trainer and Certified Nutrition Coach by the National Academy of Sports Medicine, and a Board Certified Medical Affairs Specialist by the Accreditation Council for Medical Affairs. He has graduate certificates in Digital Storytelling and Marketing Management & Digital Strategy from Harvard Extension School and certificates in Business Law and Corporate Governance from Cornell Law School.

In addition to his written work, Dr. Bohl has experience creating medical segments for radio and producing patient education videos. He has also spent time conducting orthopedic and biomaterial research at Case Western Reserve University and University Hospitals of Cleveland and practicing clinically as a general practitioner on international medical aid projects with Medical Ministry International.

Dr. Bohl lives in Manhattan and enjoys biking, resistance training, sailing, scuba diving, skiing, tennis, and traveling. You can find Dr. Bohl on LinkedIn for more information.


  • Younesi, M., Knapik, D. M., Cumsky, J., Donmez, B. O., He, P., Islam, A., Learn, G., McClellan, P., Bohl, M., Gillespie, R. J., & Akkus, O. (2017). Effects of PDGF-BB delivery from heparinized collagen sutures on the healing of lacerated chicken flexor tendon in vivo. Acta biomaterialia, 63, 200–209.

  • Gebhart, J. J., Weinberg, D. S., Bohl, M. S., & Liu, R. W. (2016). Relationship between pelvic incidence and osteoarthritis of the hip. Bone & joint research, 5(2), 66–72.

  • Gebhart, J. J., Bohl, M. S., Weinberg, D. S., Cooperman, D. R., & Liu, R. W. (2015). Pelvic Incidence and Acetabular Version in Slipped Capital Femoral Epiphysis. Journal of pediatric orthopedics, 35(6), 565–570.

  • Islam, A., Bohl, M. S., Tsai, A. G., Younesi, M., Gillespie, R., & Akkus, O. (2015). Biomechanical evaluation of a novel suturing scheme for grafting load-bearing collagen scaffolds for rotator cuff repair. Clinical biomechanics (Bristol, Avon), 30(7), 669–675.

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