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Sildenafil - Uses, Dosage, Side Effects, Drug Warnings, and Precautions

Published on Jun 04, 2021 and last reviewed on Jun 20, 2022   -  8 min read


Sildenafil is a drug used to treat erectile dysfunction in men by increasing the blood flow to the penis. Learn about its uses, dosage, drug warnings, side effects, precautions, drug interactions, and more.

Sildenafil - Uses, Dosage, Side Effects, Drug Warnings, and Precautions


Sildenafil is the generic name for the prescription medication Viagra and Revatio. It is informally known as the “blue pill.” Sildenafil is available as an oral tablet, oral suspension, and an injection (can only be administered by a doctor). The oral tablet is usually used for erectile dysfunction (ED), pulmonary arterial hypertension (PAH), and to improve exercise capacity. This medicine increases blood flow to certain areas of the body by relaxing the muscles of the blood vessels.

The active ingredient in Sildenafil is Sildenafil Citrate. Avoid taking this medicine if you are also using a nitrate drug, such as Nitroglycerin or Isosorbide Dinitrate/Mononitrate for chest pain or heart problems, as it can drastically drop your blood pressure. If you experience sudden vision loss while on Sildenafil, stop taking it and get emergency medical help.

Drug Group:

Sildenafil belongs to the class of medications called phosphodiesterase 5 (PDE5) selective inhibitors. The drugs in this group inhibit the enzyme phosphodiesterase enzymes (PDEs). The medicines in this group are primarily used as remedies for erectile dysfunction and sometimes for pulmonary hypertension. The other PDE5 selective inhibitors include Dipyridamole, Tadalafil, Vardenafil, Udenafil, and Avanafil.

What Is Sildenafil Used For?

It is the most common drug used for erectile dysfunction (ED) or impotence in men. ED is when a man cannot achieve an erection, or even if he gets an erection, it is not strong enough or does not last long enough for penetrative sex.

Decreased blood flow to the penis is the cause of a poor erection. This reduced blood flow can be due to an injury or some underlying disease, or some psychological conditions. Anxiety, stress, depression, and relationship problems are the usual psychological conditions. Some of the other causes include smoking, obesity, and drinking.

Men between the ages of 50 and 70 years are more likely to develop ED. This drug is most effective if the cause of ED is physical or lifestyle-related. In cases of psychological causes, this drug might not work properly. If that is the case, psychological counseling is the best treatment option.

Important - Sildenafil does not provide protection against sexually transmitted diseases (STD). Always use a condom or other safety measures while having sex.

The other use of Sildenafil is in the treatment of pulmonary arterial hypertension (PAH). PAH is when the pressure exerted by the blood flowing in the arteries connecting the heart and the lungs is high. This drug is not recommended for use in women and children unless it is for pulmonary arterial hypertension. It makes people with lung disease more able to exercise, meaning it increases exercise tolerance.

Never take Sildenafil or any other medicine without consulting your doctor first.

How Does Sildenafil Work?

In general, Sildenafil inhibits Phosphodiesterase type-5, which results in the increase of cyclic guanosine monophosphate (cGMP). This increases the blood flow by relaxing the smooth muscles. As mentioned before, this drug is used for ED and PAH. This is how Sildenafil works for these conditions:

  1. Erectile Dysfunction (ED) - It increases the blood flow to the penis by relaxing the smooth muscles in the wall of blood vessels. This increase in the blood flow helps a man get or maintain an erection. But remember, this tablet will help get you an erection only if you are sexually aroused.

  2. Pulmonary Arterial Hypertension (PAH) - Sildenafil decreases the blood pressure in the lungs by relaxing the muscles and widening the blood vessels present in the lungs. As the blood vessels widen, there is less resistance to blood flow, and the blood pressure drops.

Onset of Action:

Between 25 % and 63 % of orally administered Sildenafil reaches the blood circulation. If taken on an empty stomach, it takes about 30 to 120 minutes to reach maximum concentration in the blood, but taking this tablet with a fatty meal increases this time by an hour. Around 80 % of this drug is excreted in feces and 13 % in the urine.

In short, the onset of action for Sildenafil is between 30 and 120 minutes after oral administration. And the action may last as long as 12 hours.


There have been no reports of habit-forming tendency in people taking Sildenafil.

Expiry Date:

Avoid taking this medicine after it expires. The expiry date will be printed on the back of the pack.

How to Use Sildenafil?

Sildenafil is available as a tablet and liquid suspension, both to be taken orally.

To treat erectile dysfunction, Sildenafil is taken around 1 hour before sexual activity, but it can be taken any time from 30 minutes to 4 hours before sexual activity. Avoid taking this medicine more than once in 24 hours. Sildenafil can be taken with food or on an empty stomach, but if you take it after a high-fat meal, the medicine might take longer to start working.

To treat PAH, Sildenafil might have to be taken thrice in a day. This can be taken with or without food. Make sure you take the tablets at around the same time daily. It is best to keep an interval of 4 to 6 hours between two doses.

If you are taking Sildenafil in the liquid form, then shake the bottle properly for 10 seconds and then take it. Always measure out your dose properly before taking it. Avoid taking it more or less.

In case you have other health conditions or are under medications, your doctor will alter your dosage accordingly. Never take Sildenafil or any other medicine unless prescribed by your doctor.

What Is the Dosage of Sildenafil?

For ED, the doctor will start with a standard dose and increase or decrease it based on your response. Make sure that you inform the doctor how well the drug is working and if you are experiencing any side effects.

Sildenafil is available in 5 mg, 20 mg, 25 mg, 50 mg, and 100 mg oral tablets.

Dosage of Sildenafil

For children, women, and patients with kidney and liver disease, the dosage will be adjusted by your doctor.

Missed Dose:

If you are taking Sildenafil for PAH, and in case you miss a dose, you can take it as soon as you remember about missing the tablet. But if it is already time for the next dose, then do not take two tablets together, as it might result in severe adverse reactions. Just skip the missed dose and take the next dosage.

What Are the Drug Warnings and Precautions?

If you have any of the following conditions, tell your doctor:

  1. Pregnancy and Breastfeeding - Sildenafil is not usually recommended for pregnant and breastfeeding women. If you are taking this medicine for PAH, the doctor will decide whether to stop the drug or stop breastfeeding, depending on your clinical condition.

  2. Low Blood Pressure (Hypotension) - If your blood pressure is low, this medicine can further decrease it. So keep monitoring your blood pressure if you are taking Sildenafil.

  3. Other Medications - If you are using Riociguat or nitrate medicines, such as Nitroglycerin, Isosorbide Dinitrate, then Sildenafil is not recommended for you as it increases the risk of severe side effects.

  4. Heart Diseases - If you have a heart or circulation disease, use this medicine with caution. In case you have a history of heart attack, stroke, or arrhythmia in the last six months, do not use Sildenafil.

  5. Surgery - Tell your surgeon about the use of Sildenafil if you need to undergo surgery.

  6. Sudden Hearing Loss - Sildenafil can result in a sudden decrease in hearing along with tinnitus (ringing or buzzing sound in the ears).

  7. Sudden Vision Loss - This drug may result in a sudden loss of vision or impair the capacity of color differentiation.

  8. Other Risk Factors - For smokers, older adults, and patients with diabetes, hypertension, high cholesterol, etc., the risk of side effects due to Sildenafil is high.

  9. Penis Deformities - This medicine increases the risk of permanent loss of sexual potency if taken by people having a deformed penis. Deformation of the penis is seen in cavernosal fibrosis or Peyronie's disease.

  10. Priapism - Prolonged and painful erection is called priapism. The erection usually lasts for more than 4 hours in such cases. Individuals with sickle cell anemia, leukemia, multiple myeloma, etc., are more likely to develop priapism. This condition can lead to tissue damage in the penis and permanent loss of sexual potency.

  11. Children - Sildenafil has been used in certain studies to treat PAH in children. But, this medicine is not ideally prescribed for children less than 18 years old. But if it is absolutely necessary, your doctor will take a call.

  12. Benign Prostatic Hypertrophy (BPH) - The medicines used for BPH (benign prostatic hypertrophy) may interact with Sildenafil and result in severe adverse effects.

  13. Avoid Self-Medication - Even though this drug is available over-the-counter in some countries, we strongly recommend that you consult a doctor before taking it. Always take Viagra under medical supervision.

What Are the Side Effects of Sildenafil?

The common side effects of Sildenafil:

The serious side effects include:

If your symptoms are mild, they will mostly go away in a few days. If you notice severe or mild symptoms, it does not go away on its own, so call your doctor immediately. Sildenafil can also cause other side effects that are not listed here, so always consult a healthcare professional if you notice any unusual symptoms.

What Are the Interactions of Sildenafil?

It is natural for all drugs to interact with other drugs, food, and supplements. This interaction can result in certain unwanted side effects. The common interactions of Sildenafil are:

What Are the Common Brands or Trade Names of Sildenafil?

  1. Tablet Viagra 100 mg.

  2. Tablet Vigour 100 mg.

  3. Tablet Vigra 100 mg.

  4. Tablet Exgra 100 mg.

  5. Tablet Omnigra 100 mg.

  6. Tablet Progra 100 mg.

  7. Tablet Bigfun 100 mg.

  8. Tablet Revatio 5 mg or 20 mg.

Before taking medicines for ED, it is essential to find the cause. If the cause is psychological, psychological counseling is needed for the best results. And for physical causes, lifestyle changes to address obesity, smoking, etc., are crucial. To know more, consult a sexologist or andrologist online!


Frequently Asked Questions


Is it safe to take Sildenafil every day?

For erectile dysfunction, never take Sildenafil more than once a day (24 hours). If your doctor has prescribed it based on your medical history and current medications, then you can take this medicine once every day.


Is Sildenafil as good as Viagra?

Sildenafil and Viagra both contain the same active ingredient, Sildenafil citrate, and have been proven to be equally effective. As Sildenafil is a generic drug, it is cheaper than Viagra.


How long does Sildenafil take to work?

It takes about 30 to 120 minutes for this drug to take effect. Consuming grapefruit juice or a high fatty meal might increase and decrease the time taken for the drug to act, respectively.


Is it fine to take 100 mg of Sildenafil?

100 mg is the maximum dosage. The ideal dosage is 25 to 50 mg. If your doctor has prescribed it, you can take one dose of 100 mg in a day and never double the dosage.


Does Sildenafil make you last longer?

Sildenafil will help you last longer if you lose your erection very fast. But, this medicine will not help you if you orgasm too early due to premature ejaculation.


Is Sildenafil dangerous?

Sildenafil is safe to take at the dosage and duration suggested by your doctor. If you take too much or take it along with other medicines or if you have an underlying heart condition, it can result in dangerous side effects.


How should I take Sildenafil for the best results?

For best results, Sildenafil should be taken 1 hour before expected sexual activity.


Does Sildenafil make you bigger?

If you have ED, blood might not flow properly in your penis, which makes your erection look smaller. Sildenafil might make your erection feel bigger than usual, as it helps pump blood into the penis, but it will not make your penis larger than it actually is.


What was Sildenafil originally used for?

Sildenafil Citrate (Viagra) was originally developed as a treatment for hypertension and angina (a type of chest pain). But during human trials, it was found to help men induce erections.


Does Sildenafil work the first time?

You can expect this tablet to work within 30 minutes. Some reports also suggest that it works as early as 12 minutes.


Is Sildenafil a steroid?

No, Sildenafil is not a steroid. As this medicine dilates blood vessels and increases blood flow, some people use Sildenafil along with anabolic steroids to help it move in the bloodstream.


Does Sildenafil raise blood pressure?

Sildenafil is not known to raise blood pressure, but it might reduce it.


Will Sildenafil work on a full stomach?

Sildenafil can be taken with food or on an empty stomach, but for the best results, avoid taking it after a high fatty meal.

Article Resources

Last reviewed at:
20 Jun 2022  -  8 min read




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