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Sildenafil 20 mg: Effectiveness & Side Effects

Mike Bohl, MD, MPH, ALM

Reviewed by Mike Bohl, MD, MPH, ALM

Written by Geoffrey Whittaker

Published 11/08/2021

Updated 01/07/2024

When it comes to penises, size isn’t everything. But the dosage size of erectile dysfunction medications? That’s something worth paying attention to.

Sildenafil citrate is a generic drug and the active ingredient in some prescription meds. It’s most popularly known as Viagra® and is used for treating erectile dysfunction (ED). Sildenafil is also sold as Revatio®, a medication marketed for the treatment of pulmonary arterial hypertension.

Depending on your health needs, your dosage of Viagra might be 25 mg (milligrams), 50 mg, or 100 mg. While 20 mg sildenafil tablets do exist, they’re FDA approved for pulmonary arterial hypertension, not erectile dysfunction. 

Most people assume they know what Viagra does — it causes erections, right? While this is true, a few uses of sildenafil extend beyond improving sexual activity. 

Besides being sold as Viagra, sildenafil is the active ingredient in Revatio, a brand-name drug. Revatio is approved by the U.S. Food and Drug Administration (FDA) for treating pulmonary hypertension, a type of high blood pressure affecting arteries in the lungs and the right side of the heart. Revatio can prevent pulmonary hypertension from worsening.

At the moment, 20-mg Viagra does not exist — but you can get Revatio in a 20-mg tablet, and it can be prescribed off label for ED.

Sildenafil may also be used off-label to treat:

  • Raynaud’s phenomenon (narrowing blood vessels in the extremities)

  • Female sexual arousal disorder

  • Mountain sickness (altitude-induced hypoxemia)

Sildenafil has a variety of uses because it’s a phosphodiesterase type 5 (PDE5) inhibitor. PDE5 inhibitors are medications that improve blood flow to certain tissues by widening the blood vessels. This means blood can flow into your penis, allowing you to have a decent erection.

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Viagra is available in dosages of 25 mg, 50 mg and 100 mg. At present, 100-mg sildenafil is the highest dosage approved by the FDA. Revatio is available in 20-mg tablets. 

There’s no one-size-fits-all solution when it comes to the ideal sildenafil dosage. Your dosage will depend on your unique health needs and the reason you’re taking the medication.

You might assume a higher dosage of sildenafil leads to a firmer erection or better sexual performance, but this isn’t always the case. In fact, taking too much sildenafil can lead to some serious side effects. 

It’s best to stick with the dosage recommended by the healthcare professional who prescribed the medication. If your current dose isn’t working as well as you hoped, make an appointment with your provider and ask if you can revisit your dosage or explore other treatment options for erectile dysfunction.

To get the best results from Viagra, it’s important to take the right dosage. 

As mentioned, 20-mg sildenafil is FDA-approved for pulmonary arterial hypertension, not erectile dysfunction. If you take a 20-mg dose of sildenafil, it might improve your erections.

Although Viagra can come in as small a dose as 25 mg, the 50-mg tablets are usually the starting dose. If you experience uncomfortable side effects, your dosage could decrease to 25 mg. Patients older than 65 and those with kidney or liver problems may start on a 25 mg dose.

Viagra is considered an effective treatment for erectile dysfunction — but its efficacy depends on the dosage. In clinical trials, 63 percent of participants who took 25-mg sildenafil reported an improvement in their erections, compared to 74 percent of those who took 50 mg and 82 percent of those who took 100 mg.

With that said, other erectile dysfunction treatments — like tadalafil (Cialis®) and vardenafil (Levitra®) — are available in a 20-mg dosage — but these are different medications, so their dosages aren’t directly comparable to sildenafil’s. 

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Whether you’re experiencing poor erectile function or have a cardiovascular condition, sildenafil can drastically improve your symptoms.

The medication is generally safe, and research suggests it won’t cause any long-term health issues. But that doesn’t mean it’s completely without risks or side effects.

Common side effects of sildenafil include:

  • Headache 

  • Flushing

  • Back pain

  • Blurred vision

  • Muscle pain

  • Nausea

  • Dizziness

  • Rash

  • Nasal congestion

If you experience priapism (a prolonged, painful erection) or any other serious adverse effects — like shortness of breath, irregular heartbeat or loss of vision — seek emergency medical attention. 

Sildenafil might also be dangerous for people with a history of certain medical conditions, including:

  • Allergic reactions to Viagra or any PDE5 inhibitor

  • Blood problems like hemophilia, leukemia or sickle cell anemia 

  • Conditions affecting penis shape, like Peyronie’s disease or a curved penis

  • Eye problems, such as retinitis pigmentosa, vision loss or NAION (non-arteritic anterior ischemic optic neuropathy)

  • Heart problems (e.g., having had a heart attack or stroke)

  • High or low blood pressure  

  • Liver disease 

  • Kidney disease

  • Peptic ulcers

There are a few sildenafil drug interactions you need to look out for too. An interaction is when one drug, like sildenafil, causes a negative reaction when mixed with another medication, supplement or substance. 

Possible sildenafil interactions include:

  • Other PDE5 inhibitors, including erectile dysfunction medications like tadalafil (Cialis), avanafil (Stendra®) or vardenafil (Levitra® or Staxyn®) 

  • Nitrates, such as nitroglycerin (Nitrostat® or NitroMist®), isosorbide mononitrate and isosorbide dinitrate (Isordil®) 

  • Blood pressure drugs and alpha-blockers

  • Poppers (recreational drugs containing nitrites)

Sildenafil may also have minor interactions with the following substances:

  • Certain antifungal drugs, such as ketoconazole and itraconazole 

  • Some antibiotics, like erythromycin and clarithromycin (Biaxin®)

  • HIV protease inhibitors, like saquinavir mesylate (Invirase®) and ritonavir (Norvir®) 

If you’ve been prescribed any of the above medications, it’s a good idea to ask a healthcare professional whether you can safely take them with sildenafil.

Also, while you can mix Viagra with alcohol, it’s a good idea to pace yourself and only have one or two drinks.  

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Erectile dysfunction is just the tip (heh) of the iceberg when it comes to sildenafil’s potential. The dosage of sildenafil you use will depend on whether you’re taking it for erectile dysfunction, a cardiovascular condition or another issue.

  • A 20-mg dose of sildenafil is FDA approved for pulmonary arterial hypertension. That said, it it sometime prescribed off label (at the 20 mg dose and at multiples of 20 mg, including 40 mg, 60 mg, 80 mg, and 100 mg) for ED.

  • For ED, 50 mg is the typical starting sildenafil dosage. Though it can be increased or decreased as needed, licensed prescribers usually start patients on a 50-mg tablet.

  • There are some alternatives. If the side effects of sildenafil are putting you off, or if it’s just not working as well as you’d hoped, other erectile dysfunction treatments may be more helpful. Examples include tadalafil (Cialis), Stendra (avanafil), and our chewable ED hard mints.

Our guide on how to take sildenafil for erectile dysfunction covers some need-to-know info on Viagra, but it’s no replacement for speaking with a licensed healthcare professional.

If you’re concerned about your sildenafil dosage or are experiencing uncomfortable side effects, you’re wise to see medical advice from a healthcare professional.

If that sounds good, you can start today by booking an online appointment with a healthcare practitioner through our telehealth platform.

13 Sources

  1. Definition & Facts for Erectile Dysfunction - NIDDK. (2017, July). National Institute of Diabetes and Digestive and Kidney Diseases. Retrieved July 24, 2023, from
  2. Dhaliwal A, Gupta M. PDE5 Inhibitors. (2023). In: StatPearls internet. Treasure Island (FL): StatPearls Publishing. Available from:
  3. Drug Interactions between clarithromycin and Viagra. (n.d.). Available from:
  4. Drug Interactions between ciprofloxacin and Viagra. (n.d.). Available from:
  5. Li, H., Bai, G., Zhang, X., Shi, B., Liu, D., Jiang, H., Ji, Z., Davis, M. R., Zhu, Z., & Fang, Y. (2017). Effects of Two Different Dosages of Sildenafil on Patients With Erectile Dysfunction. American journal of men's health.
  6. 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.
  7. Sildenafil: Medlineplus drug information. (n.d.).
  8. Smith BP, Babos M. Sildenafil. (2023). In: StatPearls internet. Treasure Island (FL): StatPearls Publishing. Available from:
  9. Sooriyamoorthy T, Leslie SW. Erectile Dysfunction. (2023). In: StatPearls internet. Treasure Island (FL): StatPearls Publishing. Available from:
  10. Table 2. Phosphodiesterase-5 (PDE5) Inhibitors: Product Comparison. (n.d.).
  11. The Food And Drug Administration. (2017). VIAGRA® (sildenafil citrate) tablets, for oral use.
  12. The Food And Drug Administration. (2017). REVATIO (sildenafil) tablets, for oral use.
  13. Vizza, C. D., Sastry, B. K., Safdar, Z., Harnisch, L., Gao, X., Zhang, M., Lamba, M., & Jing, Z. C. (2017). Efficacy of 1, 5, and 20 mg oral sildenafil in the treatment of adults with pulmonary arterial hypertension: a randomized, double-blind study with open-label extension. BMC pulmonary medicine.
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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