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Last updated: Jan 20, 2022
5 min read

Is 20 mg an effective dose of sildenafil?

yael cooperman

Medically Reviewed by Yael Cooperman, MD

Written by Michael Martin


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.

Sildenafil 20 mg is a dosage approved for the treatment of a lung condition called pulmonary arterial hypertension (PAH). The medication is the same as the active ingredient in Viagra, which is used to treat erectile dysfunction usually in doses of 25 mg, 50 mg, or 100 mg, but healthcare providers can also prescribe sildenafil 20 mg if they think it’s the best treatment option for you. 

So how do you know if 20 mg is the right treatment for you? Read on to learn more. 

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What is sildenafil 20 mg?

Sildenafil (brand name Revatio; see Important Safety Information) is typically used as a treatment for a lung condition called pulmonary arterial hypertension (PAH). The medication works by relaxing blood vessels to improve blood flow, and can be used as a treatment for erectile dysfunction for the same reason. 

The FDA approved the 20 mg dosage (brand name Revatio) for the treatment of PAH and the 25 mg, 50 mg, and 100 mg dosages (brand name Viagra) for the treatment of erectile dysfunction. Both Revatio and Viagra contain the same medication, so even though the 20 mg dose is technically approved for the treatment of a lung condition, it can be prescribed off-label for the treatment of erectile dysfunction (DailyMed, 2018).

Why use sildenafil 20 mg?

If your healthcare provider is considering prescribing sildenafil for the treatment of ED, the traditional starting dose is 50 mg. But this dose might not be effective for everyone, or it may cause side effects for some people. Since generic Viagra is only available in dosages of 25 mg, 50 mg, and 100 mg, the prescribing options are limited. Clinicians can opt to prescribe 20 mg sildenafil (or multiples of 20 mg) to give their patients a more precise dose. 

Money also plays a role. Brand name Viagra is expensive and can cost upwards of $70 per dose. Opting for the generic Viagra lowers the price, and opting for generic Revatio in 20 mg increments can be an even more pocket-friendly option.

So why would you want to take 20 mg sildenafil when 25 mg is available? Here are some possible scenarios: 

  • Your healthcare provider may want to start you at 20 mg and see how it works.
  • You might experience side effects on 25 mg or 50 mg, but less so (or not at all) on 20 mg or 40 mg. 
  • 50 mg might not be as effective as 60 mg for you, and you and your health provider agree a slightly higher dose is better.

As a rule of thumb, it’s best to take the lowest effective dose of a drug in order to avoid potential side effects. Prescribing sildenafil in 20 mg increments can make it easier for your healthcare provider to find the dose that’s best for you—one that maximizes sildenafil’s benefits while minimizing potential side effects. 

How long does sildenafil 20 mg last? 

Sildenafil starts working within 30-60 minutes, and typically works for up to four hours, so you should plan accordingly. Keep in mind that the drug doesn’t instantly give you an erection when it kicks in. Instead, it helps you get and maintain an erection when you get aroused. 

If you’ve taken a dose of Viagra and it doesn’t work, do not take another dose before 24 hours have passed. If you find that the dosage you’ve been prescribed isn’t effective, consult with your prescribing physician to see if you need a higher dose or a different medication altogether. 

What other treatment options are there?

While Viagra is typically an effective treatment for erectile dysfunction, there are other similar medications that might be better treatment options for you. Other similar medications include: 

Sildenafil and these other medications, all known as PDE5 inhibitors, work by suppressing an enzyme called PDE5, a.k.a. an erection’s “off switch.” The “on switch” is a natural chemical called cGMP, which tells blood vessels in the penis to dilate and fill with blood. PDE5 breaks down cGMP, allowing blood to flow out of the penis. When PDE5 is blocked, blood vessels in the penis stay dilated. This makes erections stay harder for longer.

Although PDE5 inhibitors all work on the same natural chemical—PDE5—that doesn’t mean they’re all the same. Sildenafil may take 30 minutes to work and may last for 4 to 5 hours. Avanafil can be taken 15 minutes before sexual activity, and it remains effective for about the same time as sildenafil. Tadalafil comes in two formulations: one is taken daily, the other as needed and can be effective for up to 36 hours.

Picking the right medication for you might involve a little bit of back and forth with your provider, but if you see a medication you’ve been prescribed isn’t working as well as you would like, let them know. Getting the right medication and the right dosage can improve your sex life significantly.

What causes ED?

ED is the most common sexual dysfunction. Experts believe that around 30 million American men have experienced ED at some point (Nunes, 2012). ED can happen at any age, but it becomes more common as men get older. By the time a man is in his 40s, he has about a 40% chance of having experienced ED at some point. That likelihood increases by about 10% for each successive decade of life (Ferrini, 2017).

That said, ED is not considered a “natural” part of aging. It’s important to know that many different underlying health conditions can contribute to it, and that addressing those conditions can often help improve symptoms of ED. These conditions include:

That’s why it’s important to check in with a healthcare provider at the first sign of ED. They’ll evaluate your medical history, gauge your overall health, and can catch any potential health issues so you can get the treatment you need.

How to get Viagra

Viagra (sildenafil) is not available over the counter, but you can consult with a healthcare provider in person or online to get a prescription, if appropriate. 

Side effects associated with sildenafil and other ED medications include headache, facial flushing, nasal congestion, stomach upset, backache, and (rarely) temporary impaired color vision. If you experience vision changes, chest pain, or priapasm (an erection lasting more than four hours) seek medical attention immediately.  

Sildenafil and other PDE5 inhibitors 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 that could be fatal.

When buying sildenafil online, beware of counterfeiters. You’ve seen them: At some point in your web-surfing history, you’ve probably wandered into an explosion of pop-up ads hawking Viagra for mere cents on the dollar. Many of the establishments behind these ads are not legit, and the product they sell can be dangerous.

In 2011, Pfizer, the manufacturer of Viagra, investigated counterfeits by buying them online and testing their contents. Some of the pills they received contained blue printer ink, amphetamines (“speed”), an antibiotic called metronidazole, too much of the active ingredient sildenafil (or not enough), and drywall (Pfizer, n.d.). 

So if you’re interested in taking sildenafil to resolve ED, do your due diligence. Check in with a healthcare provider and get a prescription from a reputable source. 


  1. Barnett, C. F. & Machado, R. F. (2006). Sildenafil in the treatment of pulmonary hypertension. Vascular Health and Risk Management, 2(4), 411–422. doi: 10.2147/vhrm.2006.2.4.411. Retrieved from
  2. DailyMed. (2020). SILDENAFIL tablet. Retrieved on Sep. 2, 2020 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. doi: 10.1046/j.0306-5251.2001.00034.x. Retrieved from
  4. Ferrini, M. G., Gonzalez-Cadavid, N. F., & Rajfer, J. (2017). Aging related erectile dysfunction-potential mechanism to halt or delay its onset. Translational Andrology and Urology, 6(1), 20–27. doi: 10.21037/tau.2016.11.18, Retrieved from 
  5. Nunes, K. P., Labazi, H., & Webb, R. C. (2012). New insights into hypertension-associated erectile dysfunction. Current Opinion in Nephrology and Hypertension, 21(2), 163–170. doi: 10.1097/mnh.0b013e32835021bd. Retrieved from
  6. Pfizer. (n.d.). Viagra: Avoid counterfeits. Retrieved on Sep. 1, 2020 from