Is Sildenafil 20mg an Effective Dose?

By Sarah Malka, MD
Medically reviewed
May 10, 2021

Sildenafil is a pharmaceutical medication that is FDA-approved to treat erectile dysfunction (ED) in men and pulmonary arterial hypertension (PAH), a form of high blood pressure, in both men and women. It is one of only four phosphodiesterase inhibitors (PDE5 inhibitors) commercially available on the market today. Other PDE5 inhibitors include tadalafil (Cialis), vardenafil (Levitra), and avanafil (Stendra).

PDE5 inhibitors work by blocking the enzymes that inhibit blood flow in parts of your body. When men with erectile dysfunction take sildenafil, it helps the arteries in their penis expand to allow more blood flow and firmer, longer-lasting erections. When people PAH take sildenafil, the medication helps open up any narrowed arteries in their lungs and improve their circulation during periods of exercise.

In this article, I’ll explain what sildenafil is, how it compares to Viagra, and how to know if 20 mg of sildenafil is an effective treatment for you.

What Is Sildenafil?

Sildenafil (also called sildenafil citrate) is a prescription drug used to treat erectile dysfunction in men and pulmonary arterial hypertension (PAH) in men and women. It works by blocking the enzymes that make it more difficult for blood vessels to dilate and circulate freely through your body. 

In 1998, Pfizer patented sildenafil under the brand name Viagra and began selling it to consumers worldwide. In 2005, the FDA re-approved sildenafil to treat people with PAH. To make sure that everyone could tell the difference between the two drugs, Pfizer marketed this new use of sildenafil under the name Revatio.

When Pfizer’s patent on sildenafil expired, it allowed cheaper generic forms of the medication to hit the market. These drugs are identical to Viagra and Revatio but are usually sold under the name sildenafil.

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Is Sildenafil 20 mg the Same as Viagra?

Sildenafil is the generic form of Viagra, meaning it is bioequivalent to the brand-name drug. It contains the same active ingredients in identical amounts, and it helps people manage their medical conditions in the same way. There are only two differences between a generic medication and a brand-name medication: the inactive ingredients list (the ingredients that have no therapeutic effect) and the drug’s cost. Generics are generally cheaper than brand-name drugs.

Because generic drugs and brand-name drugs are identical, their dosages should act identically. There is no reason to suspect that 20 milligrams (mg) of sildenafil wouldn’t work the same way 20 mg of Viagra would work for someone taking the medication to treat ED.

What Dosages Are Available for Sildenafil?

Sildenafil is available in 25 mg, 50 mg, and 100 mg dosages. The dosage prescribed depends on your age and overall health, the severity of your condition, how well you respond to the drug, and any other medications you take.

If you suffer from heart problems or have a history of heart attack, heart failure, or other cardiovascular issues, your healthcare provider may prescribe a lower dose of sildenafil to avoid any adverse effects from taking the drug.

Sildenafil also comes with a risk of drug interactions with certain pharmaceuticals, particularly nitrates, nitroglycerin, or alpha-blockers. If you take any of these, sildenafil may not be right for you.

What Are the Side Effects of Sildenafil 20 mg?

Sildenafil can cause mild to moderate side effects, even when taken as prescribed or at low doses. Possible side effects include:

  • Bloody, congested, or runny nose
  • Tenderness around the eyes 
  • Headache
  • Muscle ache
  • Back pain
  • Warm skin on the face, neck, or chest
  • Indigestion
  • Nausea
  • Diarrhea
  • Difficulty sleeping (insomnia)
  • Unusual weakness or exhaustion 
  • Blurred vision
  • Light sensitivity
  • Buzzing in the ears
  • Confusion
  • Difficulty breathing 

If you experience any of the following side effects after taking sildenafil, seek emergency medical attention immediately: 

  • Feeling faint
  • Difficulty breathing 
  • Sudden changes in vision, vision loss, or hearing loss 
  • Swollen hands, ankles, or feet
  • Chest pain or heart attack symptoms
  • A seizure 
  • A painful erection or an erection that lasts more than four hours 

Patients who have experienced a heart attack, stroke, irregular heartbeat, or low blood pressure should be very careful before taking sildenafil. Although it can still be therapeutic for certain people with stabilized heart conditions, it can cause dangerously low blood pressure for others, particularly when combined with nitrates (glyceryl trinitrate (GTN), isosorbide dinitrate, and isosorbide mononitrate). Talk to your doctor about taking a low dose of sildenafil and whether that will help you avoid potential complications. 

Sildenafil can also cause permanent vision loss in people with certain pre-existing eye conditions. If you are at risk of non-arteritic anterior ischemic optic neuropathy (NAION) or retinitis pigmentosa, talk to your doctor before taking sildenafil or any other ED medication.

Lastly, never take more sildenafil than a doctor prescribes or combine it with street drugs like amyl nitrite (poppers). Increasing your dosage or combining it with other drugs can raise the likelihood of experiencing a severe side effect. 

How Long Does 20 mg of Sildenafil Last?

If you take sildenafil to treat erectile dysfunction, take one oral tablet at least 30 minutes and no more than four hours before sexual activity. Brief disclaimer: Watch what you eat beforehand. If you have recently ingested fatty food or alcohol, it can slow the drug’s effects. Also never take more than one pill per 24-hour period.

The amount of time that sildenafil affects someone depends on their weight, age, and other health factors, but the pill usually wears off after 4-6 hours. Note that your erection should never last more than four hours. If it does, seek medical treatment. You are at risk of developing priapism, a condition that can damage your penis if you do not see a doctor. 

If you take sildenafil to treat pulmonary arterial hypertension (PAH), take your pill or oral suspension with or without food as directed by your doctor. Your doctor may instruct you to take your medication up to three times a day (between 4-6 hours apart). Still, your dosage will depend on your condition’s severity and any other medications you may be taking.

To ensure that it stays as effective as possible, always read the drug information that comes with your medication and store sildenafil at room temperature and away from moisture.

What Should I Do If 20 mg of Sildenafil Isn’t Working?

If you take it to treat erectile dysfunction, sildenafil will only work when you combine it with sexual stimulation. If nothing turns you on, the pill will not give you an erection.

If you take your first dose of sildenafil, combine it with sexual stimulation, and don’t feel any effects, stay patient. People metabolize the drug at different speeds; depending on your age, weight, and diet, you may find that it takes you a bit longer than average to experience results. You can always help the drug work more quickly by eating a light meal and avoiding alcohol before taking it. 

If you have waited a few hours and still are not experiencing any results, call your doctor for medical advice. They may adjust your dose to help it to work as expected. 

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How Much Does 20 mg of Sildenafil Cost?

Since sildenafil is generic, it’s less expensive than its brand-name counterparts, Viagra and Revatio. The drug’s cost varies depending on your insurance coverage, recommended dosage, and pharmacy. You can compare sildenafil price options for different dosages here.

How to Get Sildenafil 20 mg Online

If you are interested in a prescription for sildenafil, contact your doctor or speak to an online health care professional to discuss your symptoms and any concerns and get a diagnosis. 

If your provider recommends sildenafil, once you have a prescription, it’s easy to buy sildenafil online. Be sure that you purchase your medication from a reputable, licensed pharmacy. Many websites sell imposter or counterfeit sildenafil and other erectile dysfunction medications, which can be dangerous to your health. 

How K Health Can Help

K Health provides a simple, accessible option for ED treatment. Chat with a doctor on your phone to determine whether you are experiencing ED. Your doctor will then prescribe you medication, which can be picked up at a local pharmacy or shipped discreetly directly to you.

Frequently Asked Questions

Is sildenafil 20 mg the same as Viagra?
Sildenafil is the generic form of Viagra, meaning that it is bioequivalent to the brand-name drug. It has the same active ingredients in the same amounts, and it helps people manage their medical conditions in the same way.
Will sildenafil 20 mg really work?
If your doctor has given you the correct prescription and you take it as directed, 20 mg of sildenafil should work without a problem.
What does sildenafil 20 mg do?
Sildenafil works by blocking the enzymes that make it more difficult for blood vessels to dilate and circulate freely through your body. Increasing blood flow to the penis helps men with erectile dysfunction more easily achieve and maintain an erection. In people diagnosed with pulmonary arterial hypertension, the increased blood flow helps open up narrowed arteries in the lungs and allows them to participate in physical activity.
How long does sildenafil 20 mg last?
The amount of time that sildenafil affects someone depends on their weight, age, and other health factors, but the pill usually wears off after 4-6 hours.
K Health articles are all written and reviewed by MDs, PhDs, NPs, or PharmDs and are for informational purposes only. This information does not constitute and should not be relied on for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment.

Sarah Malka, MD

Dr. Sarah Malka is a board certified emergency medicine physician with K Health. She completed her residency at Harvard Medical School.