Complete BNF Sildenafil Guide for UK Patients

Sildenafil is a widely prescribed PDE5 inhibitor used to treat erectile dysfunction in adult men across the UK. Listed in the British National Formulary (BNF), this prescription medication works by increasing blood flow to help achieve erections when sexually stimulated. EverydayMeds offers both generic sildenafil and branded Viagra, allowing patients to choose their preferred option following an online consultation with our UK-licensed prescribers.

  • How sildenafil works as a PDE5 inhibitor to treat erectile dysfunction
  • Available dosages, administration guidelines and effectiveness timeframes
  • Eligibility criteria and contraindications based on BNF guidance
  • Important drug interactions and safety considerations for UK patients
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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.

Understanding BNF Sildenafil: Medical Information & Usage

What is BNF Sildenafil and How Does It Work?

Sildenafil citrate is a phosphodiesterase type 5 (PDE5) inhibitor that appears in the British National Formulary as a prescription-only medicine for erectile dysfunction. The medication works by blocking the PDE5 enzyme, which helps increase blood flow to penile tissue during sexual arousal. It's important to understand that sildenafil does not cause automatic erections - sexual stimulation is still required for the medication to be effective.

BNF Dosage Guidelines and Administration

According to BNF guidance, sildenafil is available in 25mg, 50mg, and 100mg tablet strengths. The typical starting dose is 50mg, taken approximately 30-60 minutes before anticipated sexual activity. Based on individual response and tolerability, the dose may be adjusted to 25mg or increased to a maximum of 100mg. Patients should not exceed one dose within any 24-hour period. Food, particularly fatty meals, may delay the onset of action.

Eligibility and Clinical Assessment Requirements

The BNF specifies that sildenafil is indicated for adult men diagnosed with erectile dysfunction. Before prescribing, healthcare providers must conduct a thorough clinical assessment that includes cardiovascular health evaluation, current medication review, and medical history analysis. At EverydayMeds, our UK-licensed prescribers follow these BNF guidelines during online consultations to ensure patient safety and treatment suitability.

Contraindications and Safety Considerations

The BNF clearly outlines several contraindications for sildenafil use. Patients taking nitrates (such as GTN spray or isosorbide mononitrate) must not use sildenafil due to potentially dangerous blood pressure interactions. Other contraindications include severe cardiovascular disease, recent heart attack or stroke (within six months), severe liver impairment, and significant hypotension. Patients with hereditary degenerative retinal disorders or known allergies to sildenafil should also avoid this medication.

Drug Interactions and Monitoring

The BNF highlights several important drug interactions that require careful consideration. Besides nitrates, sildenafil can interact with alpha-blockers (potentially causing symptomatic hypotension), certain antifungal medications, HIV protease inhibitors, and some antibiotics. Patients taking these medications may require dose adjustments or alternative treatments. Regular monitoring may be necessary for patients with underlying cardiovascular conditions or those taking multiple medications.

Choosing Between Generic Sildenafil and Branded Viagra

Both generic sildenafil and branded Viagra contain the same active ingredient and are clinically equivalent according to MHRA regulations. The choice between generic and branded versions often comes down to patient preference and cost considerations. EverydayMeds provides both options during the checkout process, allowing patients to make an informed decision following their approved consultation. Both formulations follow the same BNF guidelines for dosing and safety monitoring.

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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