Sildenafil BNF: Essential Prescribing Information

This comprehensive sildenafil BNF reference provides healthcare professionals and patients with essential prescribing information for erectile dysfunction treatment. Covering dosages, contraindications, and clinical considerations from British National Formulary guidelines, this guide supports informed decision-making. EverydayMeds offers both sildenafil (generic) and Viagra (branded) options, allowing patients to choose their preferred treatment following clinical assessment by UK-licensed prescribers.

  • Standard dosing: 25mg, 50mg, 100mg tablets with 50mg typical starting dose
  • Contraindications include nitrate medications and severe cardiovascular disease
  • Clinical assessment required before prescription through registered UK pharmacy
  • Both generic sildenafil and branded Viagra available at checkout
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Not sure which one? Here's the honest comparison.

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

Clinical Guidelines and Prescribing Information

BNF Dosage and Administration

According to BNF guidelines, sildenafil for erectile dysfunction is available in 25mg, 50mg, and 100mg tablets. The recommended starting dose is typically 50mg, taken approximately one hour before sexual activity. Based on effectiveness and tolerability, the dose may be adjusted to 25mg or increased to a maximum of 100mg. Only one dose should be taken within any 24-hour period. EverydayMeds provides both sildenafil (generic) and Viagra (branded) formulations at these standard strengths.

Contraindications and Cautions

The BNF clearly outlines important contraindications for sildenafil use. Patients taking nitrate medications (such as GTN spray or isosorbide mononitrate) must not use sildenafil due to potentially dangerous hypotensive effects. Other contraindications include severe cardiovascular disease, recent myocardial infarction or stroke within six months, severe hepatic impairment, and hypotension. Patients with hereditary degenerative retinal disorders or known hypersensitivity to sildenafil should also avoid treatment.

Drug Interactions and Monitoring

BNF guidance emphasises several significant drug interactions requiring careful consideration. Alpha-blockers may enhance hypotensive effects, whilst CYP3A4 inhibitors like ketoconazole or ritonavir can increase sildenafil plasma concentrations. Concurrent use with other PDE5 inhibitors is contraindicated. Healthcare professionals should review all current medications during clinical assessment to identify potential interactions.

Clinical Assessment Requirements

Before prescribing sildenafil, a comprehensive clinical assessment is mandatory. This includes evaluation of cardiovascular status, current medication review, and assessment of underlying causes of erectile dysfunction. EverydayMeds ensures all patients complete this assessment with UK-licensed prescribers before treatment initiation. Patients can then choose between generic sildenafil or branded Viagra based on personal preference and budget considerations.

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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