BNF Sildenafil: Essential Guidelines Checklist

Our comprehensive BNF sildenafil checklist covers essential British National Formulary guidelines for safe erectile dysfunction treatment. Whether you're considering sildenafil (generic) or Viagra (branded), this quick reference guide provides crucial safety information, dosage guidelines, and contraindications based on current NHS prescribing standards to help you understand treatment requirements.

  • Check contraindications including nitrate medications and severe heart conditions
  • Verify appropriate starting dose (typically 50mg) and maximum once-daily frequency
  • Review drug interactions especially with blood pressure medications
  • Confirm eligibility through proper clinical assessment with UK-licensed prescriber
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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 Sildenafil Safety & Prescribing Guide

BNF Dosage Guidelines for Sildenafil

According to British National Formulary guidelines, sildenafil is available in 25mg, 50mg, and 100mg tablets. The standard starting dose is 50mg, taken approximately one hour before sexual activity. Dosage may be adjusted to 25mg if side effects occur, or increased to 100mg if 50mg proves insufficient. Both generic sildenafil and branded Viagra contain the same active ingredient - patients can choose either option during checkout based on preference and budget.

Critical Contraindications Checklist

The BNF clearly states that sildenafil must not be used by patients taking nitrate medications such as glyceryl trinitrate (GTN spray) or isosorbide mononitrate, as this combination can cause dangerous blood pressure drops. Other absolute contraindications include severe cardiovascular disease, recent heart attack or stroke (within 6 months), severe liver impairment, and hypotension. Patients with hereditary retinal disorders should also avoid sildenafil treatment.

Important Drug Interactions

Healthcare professionals must review all current medications before prescribing sildenafil. Alpha-blockers used for prostate problems can enhance hypotensive effects, requiring careful monitoring. CYP3A4 inhibitors like ritonavir and ketoconazole may increase sildenafil levels, necessitating dose reduction. Blood pressure medications may require adjustment, and patients should inform prescribers about all supplements and over-the-counter medicines.

Clinical Assessment Requirements

BNF guidelines emphasise that sildenafil requires proper clinical assessment by a UK-licensed prescriber. This includes cardiovascular risk evaluation, medication review, and assessment of underlying causes of erectile dysfunction. EverydayMeds ensures all consultations meet these standards, with patients able to choose between sildenafil (generic) or Viagra (branded) following successful assessment. The medication typically works within 30-60 minutes and effects may last 4-6 hours, though sexual stimulation remains necessary for effectiveness.

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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