Viagra dosage, forms, and strengths

Viagra is a brand-name prescription medication manufactured by Pfizer for the treatment of erectile dysfunction. The active ingredient in Viagra, sildenafil citrate, belongs to a class of drugs called phosphodiesterase type 5 inhibitors. These drugs relax arteries in the penis, causing them to widen. This increases and prolongs blood flow into the penis’ erectile tissues. 

Although brand-name Revatio (sildenafil) and its corresponding generic, sildenafil, are FDA-approved to treat pulmonary arterial hypertension (also known as PAH—which is high blood pressure in the arteries of the lungs), Viagra (and its corresponding generic equivalent, sildenafil, which is available in different dosages than Revatio) is not. Viagra is taken by mouth as a tablet with or without food anywhere from 30 minutes to four hours before anticipated sexual activity. 

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Viagra forms and strengths

Viagra and its generic are available in tablet form in three different dosing strengths. (Revatio’s generic sildenafil, however, is also available as an oral suspension or injection to treat PAH).

• Viagra and generic sildenafil: 25 milligrams (mg), 50 mg, and 100 mg tablets

• Revatio and generic sildenafil: 20 mg tablet, 10 mg/mL solution or suspension, also available as an injection

Viagra dosage for adults

Viagra is taken as needed for the treatment of erectile dysfunction.

• Standard Viagra dosage for adults: 25–100 mg taken by mouth 30 minutes to four hours before anticipated sexual activity

Viagra dosage for children

Viagra is not approved for use in children younger than 18 years of age. However, Revatio’s generic sildenafil is sometimes used off-label to treat pulmonary hypertension in children as young as newborns.

Viagra dosage restrictions

Viagra may not be an appropriate medication for everyone depending on existing medical conditions or other prescription drugs being taken. People with allergies to sildenafil will not be able to take Viagra.

Men with risk factors for non-arteritic anterior ischemic optic neuropathy (NAION), a condition in which blood flow to the optic nerve stops, are at a greater risk for vision loss. These men should carefully discuss with a healthcare provider the pros and cons of taking Viagra.

Other people who may not be suitable for Viagra include people with penis deformations such as Peyronie’s disease or any medical condition that raises the risk of prolonged and painful erections (priapism) such as leukemia, multiple myeloma, or sickle cell anemia. Anyone taking blood pressure medications should be prescribed Viagra with caution, as both can lower blood pressure. Drugs in the category of guanylate cyclase stimulators or nitrates are contraindicated with (should not be used with) Viagra.

While not directly related to the drug or its side effects, some men may not be right for Viagra because sexual activity puts them at risk for stroke or heart attack. In general, men with heart disease, heart failure, heart problems, high blood pressure, or who have experienced a recent heart attack should talk to a healthcare provider about the risks of sexual activity before taking Viagra.

For men 65 years of age or older, or who have kidney problems, a healthcare professional will start with the lowest possible dose (25 mg).

• Renal impairment (kidney disease)—starting dose adjustment: 

  • Creatinine clearance of 30–49 milliliters (mL)/min or 50-80 mL/min: no dosage restriction

  • Creatinine clearance less than 30 mL/min: Starting dose 25 mg

  • Hemodialysis: Starting dose 25 mg

  • Parenteral dialysis: Not defined

• Hepatic impairment (liver disease): Starting dose 25 mg

Viagra dosage for pets

Viagra is not approved for use in animals. However, generic sildenafil, the active ingredient in Viagra, is used off-label in dogs and cats to treat pulmonary hypertension, or high blood pressure in the arteries of the lungs. Dosing has not been standardized, so doses may vary depending on the practitioner. In general, expect to give 0.5 mg per kilogram (2.2 pounds) of body weight up to 1 mg/kg for both cats and dogs. Sildenafil will usually be administered orally 2 to 3 times daily. 

How to take Viagra 

Viagra is taken by mouth as a tablet usually one hour before anticipated sexual activity.

• Take this medicine as directed. A healthcare provider will give instructions on how much

  Viagra to take and when to take it. 

• Do not use more than directed. A healthcare provider can change the dose if needed.

• This medicine includes a medication guide or patient information. Read this information and follow the instructions and warnings. A doctor, pharmacist, or healthcare provider can answer any questions.

• Take Viagra approximately one hour before engaging in sexual activity, but the tablet can be taken anywhere from 30 minutes to four hours before engaging in sexual activity. 

• Viagra can be taken with or without food. If taken with a high-fat meal, the medicine may take longer to take effect.

• Sexual stimulation is required for this medicine to work.

• Do not take more than one dose a day. 

• Do not use other erectile dysfunction medications or over-the-counter erectile remedies such as nitrites (“poppers”) when taking Viagra.

• Store the medicine in a closed container at room temperature (68–77 F).

Viagra dosage FAQs

How long does it take Viagra to work?

Viagra should take effect in 30 to 60 minutes. Sexual stimulation is required for Viagra to be effective as an erectile dysfunction medication.

Although Viagra can be taken with or without food, Viagra takes longer to show effects if it is taken with a high-fat meal. Grapefruit and grapefruit juice should be avoided. Grapefruit contains a substance that will block the body’s metabolism of sildenafil, raising the risk and severity of side effects.

How long does Viagra stay in your system?

With a half-life of three to five hours, Viagra is completely cleared from the body in about 20 hours. However, the body breaks down sildenafil, the active ingredient in Viagra, into another substance that is about half as powerful as sildenafil at relaxing arteries. This metabolite accounts for 20% of the effects of taking Viagra and it, too, has a half-life of four hours. For this reason, Viagra can still be effective at inducing and maintaining erections four hours after being taken.

What happens if I miss a dose of Viagra?

Viagra is taken on an as-needed basis rather than on a regular dosing schedule. Take Viagra at least 30 minutes before anticipated sexual activity. If a dose is forgotten, it can still be taken. Sexual activity, however, may need to be delayed to allow the medicine time to work. Do not, however, take more than one dose each day.

How long can you take Viagra?

Viagra is prescribed on an as-needed basis. A single dose can be taken every day, but do not exceed the prescribed dose and do not take more than one dose in a single day.

How do I stop taking Viagra?

Viagra can be stopped at any time without tapering the dose. Viagra does not cause physical dependence or withdrawal when used as directed at the recommended dose.

There are, however, many reasons why men may choose to stop taking Viagra. Some may not be able to take many of the common side effects of Viagra such as headache, flushing, heartburn, nasal congestion, nausea, blurred vision, abnormal vision, muscle pain, or back pain. Some men may need to quit taking Viagra because of more serious side effects such as severe allergic reactions, vision loss, or prolonged erections (priapism). Finally, some men may need to stop taking Viagra simply because sexual activity puts them at risk for stroke or serious cardiovascular events such as chest pain (angina), heart attack, and irregular heartbeats.

Stop taking Viagra immediately and get medical help right away if any of the following are experienced when taking the medicine:

• Sudden loss of vision in one or both eyes

• Sudden hearing loss or decrease in hearing (other symptoms may include ringing in the ears and dizziness)

• Signs of an allergic reaction such as rash, hives, swelling, or difficulty breathing

The only alternative medications used in the treatment of erectile dysfunction are other PDE5 inhibitors similar to sildenafil. These include Cialis (tadalafil), Levitra (vardenafil), and Stendra (avanafil). They are very similar to Viagra, so they may not be a workable alternative for men who cannot take Viagra.

There is one medical alternative to PDE5 inhibitors like Viagra. Caverject (alprostadil) and Muse (alprostadil) both have the same active ingredient that relaxes penile tissues to allow more blood flow. However, Caverject must be injected into the penis, and Muse is administered as pellets into the urethra. Both are effective, but some men are uncomfortable with the methods in which these medicines are administered.

What is the maximum dosage for Viagra?

Men should only take the prescribed dose and never exceed more than a 100 mg dose. If the medicine does not seem to work, talk to a healthcare provider about changing the dose. No more than one dose should be taken each day.

Can you overdose on Viagra?

A Viagra overdose raises the risk and severity of side effects. Some of these can be severe such as hearing loss, vision loss, dangerously low blood pressure (hypotension), seizures, or prolonged erections (priapism) that can permanently damage the erectile tissues in the penis. If too much Viagra has been taken, call a healthcare provider or go to a hospital emergency room.

What interacts with Viagra?

Combining Viagra with other prescription drugs can cause problems. In particular, Viagra should never be taken with drugs called guanylate cyclase stimulators such as Adempas (riociguat). Other drugs that are contraindicated (should never be used with Viagra) include nitrates such as nitroglycerin pills and certain HIV antiviral medications in the protease inhibitor class, such as ritonavir or saquinavir. Viagra should also not be combined with other erectile dysfunction medicines.

Viagra lowers blood pressure, so there’s a danger of blood pressure falling too low if Viagra is combined with alpha blockers, drugs normally used to treat high blood pressure or prostate problems. Other high blood pressure drugs can also be a problem when taken with Viagra, due to additive effects on lowering blood pressure.

Other significant drug interactions with Viagra include macrolide antibiotics such as erythromycin and certain types of antifungals like ketoconazole and itraconazole. These drugs, known as CYP3A4 inhibitors, block the body’s ability to break down sildenafil, increasing its concentration in the blood and making side effects more likely and more severe.

On the other hand, some drugs speed up the body’s metabolism of sildenafil. Known as CYP3A4 inducers (such as rifampin), these drugs do not cause serious drug interactions with Viagra, but they do make it less effective at helping men get and retain an erection. When Viagra is taken with these medicines, doses might need some adjustment.

What happens when you mix Viagra and alcohol?

A moderate amount of alcohol can be consumed when taking Viagra, as long as approved by the healthcare provider. There are no documented drug interactions between alcohol and Viagra. Drinking alcohol in excess, however, can worsen sexual and erectile dysfunction, essentially neutralizing the benefits of Viagra.

Related resources for Viagra dosages:

• Sildenafil compound summary

• Sildenafil citrate drug summary

• Sildenafil citrate tablets prescribing information

• Viagra monograph

• Viagra prescribing information

• Viagra