Sildenafil: Uses Benefits and Side Effects

What is a Sildenafil?

Sildenafil is a medication that relaxes the muscles of the blood vessels and increases blood flow to particular areas of the body. It is most well-known under the brand name Viagra, which is used to treat erectile dysfunction in men. It has also been approved to treat pulmonary arterial hypertension and improve exercise capacity in both men and women.

Sildenafil belongs to a class of medications called phosphodiesterase type 5 (PDE5) inhibitors, which work by increasing blood flow to the penis and relaxing the blood vessels in the lungs.

Sildenafil comes in tablet form and is also available as a liquid that can be swallowed. It is available over the counter in some countries, but in the United States, a prescription from a doctor is required.

How Does Sildenafil Work?

In cases of erectile dysfunction, sildenafil increases blood flow to the penis, helping a man to get and keep an erection when sexually aroused. This process occurs via the nitric oxide (NO)-cyclic guanosine monophosphate (cGMP) pathway. During sexual stimulation, nitric oxide is released, increasing the level of cGMP in the corpus cavernosum, which in turn relaxes and widens the blood vessels in the penis.

Sildenafil works by blocking the enzyme cGMP-specific phosphodiesterase type 5 (PDE5) which usually breaks down cGMP. By inhibiting PDE5, sildenafil enhances the effect of nitric oxide and cGMP, and therefore increases blood flow to the penis.

How to use Sildenafil Tablet?


Sildenafil tablets are usually taken orally, and the dosage depends on the medical condition for which it is being prescribed.

For erectile dysfunction (ED), the usual dosage is 50mg, taken around 1 hour before sexual activity. The effects can last for up to 4 to 6 hours.
It is recommended that you take the tablet on an empty stomach and avoid consuming large amounts of alcohol before taking the medication. If 50mg is ineffective, your doctor may increase the dosage to 100mg.

For pulmonary arterial hypertension (PAH), sildenafil is typically taken three times a day, every 4 to 6 hours. The dosage is usually 5 or 20mg.

What are the Warnings and Precautions of the Sildenafil?

Here are some important precautions and warnings to be aware of before taking sildenafil:

Sildenafil is contraindicated in patients taking nitrates, such as those who have angina or heart problems. Taking sildenafil with nitrates can cause a dangerous drop in blood pressure.

Do not take sildenafil with guanylate cyclase stimulators, such as riociguat.

Sildenafil may interact with alpha blockers, causing blood pressure to drop too low, and should be used with caution if you are taking these medications.

Avoid alcohol and grapefruit products with sildenafil, as they can worsen side effects.

People with certain eye disorders, including inherited eye conditions, may be at risk of vision changes or loss. Those who have previously experienced eye problems, are over 50, or smoke, are also at greater risk.

Those with a deformed penis shape, such as Peyronie’s disease, have an increased risk of priapism. If an erection lasts longer than 4 hours, seek immediate medical attention as it can cause permanent damage.

Sildenafil is not recommended for children under 18, and in some cases can increase the risk of death.

Women who are pregnant or breastfeeding should consult their doctor before taking the medication.

Elderly patients and those with kidney or liver disease, or a low blood pressure of <90/50mmHg, should exercise caution when taking sildenafil and may require a lower dose.

In the case of an overdose, seek immediate medical attention. Symptoms can include severe dizziness and fainting.

What are the Side Effects of Sildenafil?


The most commonly reported side effects of sildenafil are mild and include:

  • Headaches
  • Flushing
  • Rhinitis
  • Dizziness
  • Hypotension
  • Postural hypotension
  • Dyspepsia
  • Blue-green colour tinted vision and blurred vision
  • Unexplained myalgia
  • Nasal congestion
  • Heartburn
  • Indigestion
  • Diarrhoea
  • Stomach cramps

There are also some more serious side effects that require immediate medical attention, including:

  • Painful or prolonged erection (prolonged erections can cause damage)
  • Vision changes or sudden vision loss
  • Ringing in the ears or sudden hearing loss
  • Irregular heartbeat
  • Swelling of the face, hands, feet or lower legs
  • Difficulty breathing or concentrating.
  • Fainting
  • Seizure
  • Chest pain or pressure, or pain spreading to the jaw or shoulder.

Sildenafil should not be used by people who are also using a nitrate drug for chest pain or heart problems, as it can cause a serious decrease in blood pressure.

If any of these side effects are experienced, you should speak to your doctor as soon as possible.

How Does Sildenafil Interact with Other Medicines?

Sildenafil should not be taken by anyone who is also using a nitrate drug for chest pain or heart problems, as it can cause a serious drop in blood pressure. This includes nitrates such as nitroglycerin, isosorbide and amyl nitrite.

It also must not be taken with other medications for pulmonary arterial hypertension, such as riociguat, or other erectile dysfunction drugs, including avanafil, tadalafil and vardenafil.

The medication can also interact with alpha blockers, blood pressure drugs, antifungal drugs, HIV protease inhibitors, antibiotics, St John’s Wort, and grapefruit.

As with other medications, sildenafil may also interact with supplements or vitamins, so consult your doctor or pharmacist if in doubt.

What happens if I miss a dose of sildenafil?

If you miss a dose of sildenafil, the course of action depends on whether you are taking the medication for erectile dysfunction (ED) or pulmonary arterial hypertension (PAH).

If you miss a dose of sildenafil and are taking it for ED, take the dose 30 minutes to 4 hours before your next sexual activity, or as soon as you remember. However, if it’s nearly time for your next scheduled dose, just leave out the missed dose and take the next dose at the usual time. Do not take two doses at once.

If you are using sildenafil to treat PAH, take the missed dose as soon as you remember, unless it’s almost time for your next scheduled dose. In this case, skip the missed dose and continue with the next one. Never take two doses at the same time.

What happens if I overdose on Sildenafil?

An overdose of sildenafil can cause dangerous levels of the drug to build up in your body. Symptoms of an overdose can include blurred vision, visual changes, hearing problems, low blood pressure, and a prolonged and painful erection (known as priapism).

Some cases of sildenafil overdose have resulted in death. In at least one case, a 56-year-old man was found dead at home after overdosing on sildenafil, which caused cardiomegaly and diffuse coronary atherosclerosis.

If you think you have overdosed on sildenafil, call your doctor or a poison control center right away, or attend the nearest emergency room.

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