What is Sildenafil?

Sildenafil is a popular tablet taken for erectile dysfunction (ED), and is more commonly recognised in its branded form, Viagra. Both contain the same active ingredient (sildenafil citrate) and work in the same way, but generic Sildenafil is the more affordable option.

Sildenafil is a PDE5 inhibitor – it binds to receptors which force blood vessels to relax. This allows greater blood flow into the penis, making it easier to get an erection. Sildenafil normally starts working 30-60 minutes after you take it.

What Doses of Sildenafil are Available?

Sildenafil comes in three standard amounts:

Dosage Use
25mg Lowest dose, typically given if 50mg tablets are unsuitable due to certain health conditions/medications
50mg Most common dose, typically given as a starting dose and increased/decreased by doctor if necessary
100mg Highest dose, typically given if 50 mg is not effective


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Your doctor may give you a 25 mg dose of Sildenafil if you have already tried the 50 mg dose and experienced negative side effects, if you are taking certain medications, or if you have certain medical conditions (such as heart problems) which could be affected by the medication.


The 50 mg dose is most commonly prescribed for first-time users, but your doctor may decide a different appropriate starting dose for you based on your health and medications. This is also the dosage of Viagra Connect, the over-the-counter version of Viagra.

Is It Ok to Take 100mg of Sildenafil?

100 mg is generally the highest recommended dose of Sildenafil, which your doctor may give as a first dose, or much more likely will be given after already trying the 50 mg dose without success.

100 mg doses of Sildenafil can be taken as one 100 mg tablet, or you can take two 50mg sildenafil tablets.

Increasing the dose of Sildenafil does not increase the length of effects, but instead increases the strength of effects – which also means that the strength of side effects might be increased. It is important to discuss any side effects with your doctor, and to not increase your own dose without first consulting your doctor.

Can I Take 200 mg of Sildenafil?

For those wondering about the highest dose of sildenafil, 200 mg may be recommended in rare cases. However, it is crucial that you discuss this with your doctor beforehand, as increasing the dosage beyond 100 mg may lead to dangerous complications.

What is the Best Dose of Sildenafil For Me?

The optimum dose of Sildenafil for any person depends on many factors such as age, health, underlying medical conditions and severity of erectile dysfunction.

For most people, the best Sildenafil dose will be 50 mg – but it is best to seek guidance from a medical professional to start at the dose they recommend, and adjust as required under their supervision.

You should take your recommended dose eight separate times (when you need it) before increasing the dosage or switching treatment.

What is the Sildenafil Dose for High Blood Pressure?

Sildenafil isn’t only used as an ED treatment; due to its effect of relaxing blood vessels, it can be used to treat pulmonary arterial hypertension (high blood pressure) as well. The normal dose for treating high blood pressure will be set by your doctor, but normally comes in at 20mg, taken three times a day.

How to Take Sildenafil

Sildenafil should be taken only once per day as required, ideally 30-60 minutes before you plan to have sex – but no more than four hours before.

It should be taken on a relatively empty stomach otherwise it may take longer to work.

How to Store Sildenafil

Sildenafil should be stored at room temperature or cooler in a dry place (i.e. not the bathroom). A refrigerator is also suitable. Make sure to store out of sight and reach of children.

How Much Sildenafil is Too Much?

As with any drug, if you take too much Sildenafil (more than once in 24 hours, or a higher dose than recommended), you may experience negative side effects. Taking too much Sildenafil may cause a drop in blood pressure, which can lead to:

  • Headache
  • Vision changes (blurry/colour changes/sensitivity to light)
  • Sudden hearing loss or ringing in the ears
  • Chest pain/shortness of breath
  • Dizziness/fainting/confusion


If you think you may have overdosed on Sildenafil, seek emergency medical help immediately.

A more serious consequence of taking too much Sildenafil is a prolonged, painful erection, known as priapism. If you have taken Sildenafil and have an erection lasting longer than four hours which is not relieved by ejaculation, you should seek medical help immediately. Left untreated, this can permanently damage penile tissues.

Can Sildenafil React With Other Medicines and Food?

Yes, Sildenafil can interact with a number of foods and medications. This is because it is broken down in the liver, and certain foods/medications can interact with it there to increase/decrease its effect.

These include:

  • Nitrates – Used to treat chest pain (angina), can cause a sudden drop in blood pressure.
  • Certain blood pressure medications – Drugs for high blood pressure (hypertension) can also cause a sudden drop in blood pressure.
  • Certain HIV medications – Can interact with Sildenafil to cause side effects.
  • Grapefruit juice – Can increase the amount of Sildenafil in your blood and delay its effect, increasing the risk of side effects.


This list only provides some examples, and is by no means exhaustive. Inform your GP of any medications you take so they can advise you on any you should avoid.

For more information about what to avoid, as well as potential side effects, please read the Patient Information Leaflet.


  • Sildenafil and Viagra (sildenafil citrate) come in a variety of strengths, and you should speak with your doctor to find the right strength for you
  • ED medications can interact with other drugs and foods – always read the Patient Information Leaflet before use


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