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Sildenafil 20mg: is it an effective dosage?

3 min read

Written by: 

Michael Martin

 and 

Ashley Laderer

Reviewed by: 

Austin Ulrich, PharmD, BCACP

Published: Nov 11, 2020

Updated:  May 22, 2026

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Reviewed By

Austin Ulrich, PharmD, BCACP

Austil Ulrich, PharmD, BCACP, is a board-certified ambulatory care pharmacist and freelance medical writer and reviewer. His experience includes direct patient care in hospitals and community pharmacies.

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Key takeaways

  • Sildenafil (Viagra) 20 mg may be effective for treating erectile dysfunction (ED) in some people; however, it is lower than the FDA-approved doses for ED. The FDA-approved doses of sildenafil for ED are 25 mg, 50 mg, and 100 mg.

  • Potential side effects include upset stomach, headache, muscle aches, or face flushing. 

  • If sildenafil 20 mg is not the right fit, other ED medications include vardenafil, tadalafil (Cialis), and avanafil (Stendra). Talk with a healthcare provider to determine which medication and dosage is right for you.

Here's what we'll cover

Here's what we'll cover

Key takeaways

  • Sildenafil (Viagra) 20 mg may be effective for treating erectile dysfunction (ED) in some people; however, it is lower than the FDA-approved doses for ED. The FDA-approved doses of sildenafil for ED are 25 mg, 50 mg, and 100 mg.

  • Potential side effects include upset stomach, headache, muscle aches, or face flushing. 

  • If sildenafil 20 mg is not the right fit, other ED medications include vardenafil, tadalafil (Cialis), and avanafil (Stendra). Talk with a healthcare provider to determine which medication and dosage is right for you.

Sildenafil 20 mg can work for erectile dysfunction (ED) in some people, but it is lower than the doses approved by the Food and Drug Administration (FDA) specifically for ED — 25 mg, 50 mg, and 100 mg. Sildenafil is the active ingredient in Viagra, an ED medication typically prescribed at those higher doses. 

Keep reading to learn about the effectiveness of sildenafil 20 mg for ED, its side effects, and alternatives.

Is 20mg of sildenafil effective for ED?

Sildenafil 20 mg may be effective for ED in some people, but it is on the lower end of the dosing range. The lowest FDA-approved dose of sildenafil for ED is 25 mg, going up to 50 mg and 100 mg. The most common starting dose is 50 mg, and a healthcare provider can adjust the dose higher or lower as necessary.

The 20 mg dosage of sildenafil is available as a generic and under the brand name Revatio, which is FDA-approved to treat a lung condition called pulmonary arterial hypertension (PAH) — not ED.

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Sildenafil 20mg: how long does it last? 

Sildenafil 20 mg starts working within 30–60 minutes and typically remains effective for about four hours.

It’s worth noting that sildenafil does not instantly cause an erection — it helps with achieving and maintaining one during sexual arousal.

It's possible that sildenafil 20 mg may not produce the desired effects. If it does not work as expected, do not take another dose within 24 hours. If the prescribed dosage is not effective, talk to your healthcare provider about a higher dose or a different medication.

Why use sildenafil 20mg?

A healthcare provider might prescribe sildenafil 20 mg off-label for ED to start at a low dose and assess how you respond. In general, taking the lowest effective dose of a medication helps minimize the risk of potential side effects.

If sildenafil 20 mg is not effective, a healthcare provider can prescribe multiple 20 mg tablets for a more tailored dose — for example, two tablets for 40 mg or three for 60 mg — rather than switching to the fixed strengths available for Viagra.

Side effects and warnings of sildenafil 20mg

The most common side effects of sildenafil 20 mg when used for ED include:

  • Headache

  • Upset stomach 

  • Face flushing

  • Nosebleeds

  • Back pain

  • Arm or leg pain

  • Muscle aches 

  • Diarrhea

More rare and serious side effects include:

  • Low blood pressure

  • Vision changes (decrease or loss of vision in one or both eyes)

  • Sudden loss of hearing or a decrease in hearing

  • Priapism (a painful erection lasting more than 4 hours) 

If you experience any of these serious side effects, seek medical attention immediately. 

Sildenafil 20 mg and other PDE5 inhibitors — including Viagra and Cialis (tadalafil) — should never be taken with nitrates or nitrites. These include prescription medications used to treat chest pain and a recreational drug called poppers. Taking sildenafil with nitrates can cause a dangerous drop in blood pressure.

How to get 20mg sildenafil  

Sildenafil is not available over the counter, but you can speak with a healthcare provider in person or online to get a prescription.

You can share your ED symptoms and overall health history, and a healthcare provider will determine whether sildenafil 20 mg is appropriate for you or whether a different dose is a better fit.

Alternatives to sildenafil 20 mg for ED

If sildenafil 20 mg is not the right option, other ED medications may be a better fit. These include:

Sildenafil and these other ED medications are PDE5 inhibitors, which work by blocking an enzyme called PDE5. PDE5 breaks down cGMP — a natural chemical that signals blood vessels in the penis to dilate and fill with blood — allowing blood to flow out of the penis. When PDE5 is blocked, blood vessels in the penis stay dilated, supporting longer-lasting erections. Although all PDE5 inhibitors target the same enzyme, they differ in onset time, duration, and dosing. Sildenafil may begin working in as little as 30 minutes and can last about four hours. Avanafil can be taken as soon as 15 minutes before sexual activity and also remains effective for about 4–5 hours. Tadalafil can be taken in two different ways — either once daily  or once as needed — and can remain effective for up to 36 hours.

Finding the right medication may take some back and forth with a healthcare provider. If sildenafil 20 mg or another option is not working as expected, it is worth discussing alternatives. The right medication and dosage can make a meaningful difference.

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Bottom line 

Sildenafil 20 mg is FDA-approved for pulmonary arterial hypertension and may also be prescribed off-label for erectile dysfunction in some people.

  • The lowest FDA-approved dose of sildenafil for treating ED is 25 mg.

  • A healthcare provider might prescribe sildenafil 20 mg to minimize the risk of side effects and assess your response. They may also prescribe multiple 20 mg tablets for a more tailored dose.

  • Sildenafil 20 mg may cause side effects such as headache, upset stomach, muscle aches, or face flushing.

  • If sildenafil 20 mg is not the right fit, a healthcare provider might recommend other ED treatments such as vardenafil (formerly sold as Levitra), tadalafil (Cialis), or avanafil (Stendra).

Frequently asked questions (FAQs)

DISCLAIMER

If you have any medical questions or concerns, please talk to your healthcare provider. The articles on Health Guide are underpinned by peer-reviewed research and information drawn from medical societies and governmental agencies. However, they are not a substitute for professional medical advice, diagnosis, or treatment.

Viagra Important Safety Information: Read more about serious warnings and safety info.

Cialis Important Safety Information: Read more about serious warnings and safety info.

Sildenafil (Generic of Viagra)
Erectile Dysfunction

References

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