Sildenafil BNF Dosage Strengths & Clinical Guidance

Sildenafil is available in three BNF-approved dosage strengths: 25mg, 50mg, and 100mg tablets. The recommended starting dose is typically 50mg, taken approximately one hour before sexual activity. Dosage may be adjusted based on individual response and tolerability. EverydayMeds offers both generic sildenafil and branded Viagra options following online consultation with UK-licensed prescribers.

  • Starting dose: 50mg taken 30-60 minutes before sexual activity
  • Lower dose: 25mg for those requiring reduced strength
  • Higher dose: 100mg maximum daily dose if 50mg insufficient
  • Maximum frequency: One tablet per 24-hour period only
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Not sure which one? Here's the honest comparison.

Sildenafil
~60 min
~4 hrs
you like to plan ahead
Tadalafil (as-needed)Most prescribed
~30 min
up to 36 hrs
you want a whole weekend covered
Tadalafil Daily
always active
continuous
you never want to think about timing
Vardenafil
~15–30 min
~8 hrs
you want the fastest onset

How ED treatment works in your body.

Increases blood flow

Increases blood flow

When PDE5 is suppressed, blood is able to flow more freely through the body—including to the (you guessed it) penis.

Increase erections

Increase erections

More blood flow to the penis means harder, more satisfying erections once you're sexually stimulated.

Complete BNF Dosage Information for Sildenafil

Reviewed by Mostafa Damghani · 03/07/2026

Standard Sildenafil Dosing Protocol

According to BNF guidelines, sildenafil for erectile dysfunction should be initiated at 50mg approximately one hour before sexual activity. This starting dose is appropriate for most men and provides an effective balance between therapeutic benefit and potential side effects. The dose may be adjusted based on individual response and tolerability.

Dosage Adjustment Guidelines

If the 50mg dose proves insufficient, it may be increased to 100mg, which represents the maximum recommended daily dose. Conversely, if side effects occur or the response is adequate at a lower dose, reduction to 25mg may be appropriate. Elderly patients or those with hepatic impairment should typically start with 25mg. It's important to note that only one dose should be taken within any 24-hour period.

Administration and Timing

Sildenafil should be taken on an empty stomach when possible, as food may delay absorption and reduce effectiveness. The medication typically begins working within 30-60 minutes, with peak plasma concentrations reached after approximately one hour. Effects may last up to four hours, though this doesn't mean an erection will persist for this duration.

Available Formulations

EverydayMeds provides both generic sildenafil and branded Viagra in all three BNF-approved strengths. Patients can choose between these options during checkout, with both containing the same active ingredient sildenafil citrate. The choice often comes down to personal preference and cost considerations, as both formulations are clinically equivalent.

Clinical Considerations

Dose adjustments may be necessary for patients with certain medical conditions. Those with severe renal impairment may require dose reduction, whilst patients taking certain medications such as ritonavir or other potent CYP3A4 inhibitors should start with 25mg. A thorough medical assessment ensures appropriate dosing for individual circumstances.

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What you need to know about erectile dysfunction

It's one of the most common conditions we treat, and one of the most treatable.

What is Erectile Dysfunction?
ED means finding it hard to get or keep an erection firm enough for sex. It's not unusual to have an off night; the point at which it's worth doing something is when it's happening regularly, or when it's starting to bother you.
How will I feel when I take ED medication?
For most men, nothing feels different day to day. The medication works in the background — when you're sexually aroused, it helps blood flow where it's needed, so erections come more easily and last longer. It doesn't cause arousal on its own. Some men notice mild, short-lived effects like a headache, facial flushing or a stuffy nose, which usually pass as the dose wears off.
Why do I need a prescription for ED medication?
ED treatments are prescription-only medicines in the UK because they aren't suitable for everyone — for example, alongside certain heart conditions or medications like nitrates. That's why we ask you to complete a short online consultation first. A UK-registered prescriber reviews your answers to make sure your chosen treatment is safe and right for you before it's dispensed.
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FAQs

Frequently asked questions

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Our UK pharmacists are happy to help. There is no charge and no obligation.

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What is the standard starting dose of sildenafil according to the BNF?
The BNF recommends a starting dose of 50mg for most men. This dose should be taken approximately 30-60 minutes before sexual activity and provides an effective balance between therapeutic benefit and tolerability.
Can I take more than 100mg of sildenafil if 100mg doesn't work?
No, 100mg is the maximum recommended daily dose according to BNF guidelines. Taking higher doses increases the risk of serious side effects without providing additional benefit. If 100mg proves insufficient, you should consult your prescriber to discuss alternative treatments.
When might a 25mg dose be prescribed instead of 50mg?
A 25mg dose may be appropriate for elderly patients, those with liver problems, severe kidney disease, or men taking certain medications that interact with sildenafil. It may also be prescribed if someone experiences side effects with higher doses but still achieves adequate therapeutic response.
How long should I wait between sildenafil doses?
You must wait at least 24 hours between doses. Taking sildenafil more frequently can lead to dangerous drops in blood pressure and increase the risk of serious cardiovascular side effects.
Is there any difference between generic sildenafil and Viagra dosing?
No, both generic sildenafil and branded Viagra contain the same active ingredient and follow identical BNF dosing guidelines. Both are available in 25mg, 50mg, and 100mg strengths with the same administration instructions and effectiveness profiles.