BNF Sildenafil: Essential Information & Guidelines

Sildenafil is a prescription medication for erectile dysfunction, classified as a PDE5 inhibitor in the BNF. This comprehensive guide provides essential clinical information about sildenafil dosing, contraindications, and safety considerations. EverydayMeds offers both generic sildenafil and branded Viagra options following online consultation with UK-licensed prescribers for your convenience and choice.

  • Available in 25mg, 50mg, and 100mg strengths with 50mg typical starting dose
  • Take 30-60 minutes before sexual activity, maximum once per 24 hours
  • Contraindicated with nitrates and in severe cardiovascular disease
  • Common side effects include headache, flushing, and nasal congestion
Start your free consultation

Takes less than 2 minutes to complete, 100% online

More pleasure. Less waiting. Built to last.

Get Started

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.

Clinical Guidelines and Prescribing Information

Mechanism of Action

Sildenafil works as a phosphodiesterase type 5 (PDE5) inhibitor, increasing blood flow to erectile tissue when sexually stimulated. The medication does not cause automatic erections and requires sexual arousal to be effective. Effects typically begin within 30-60 minutes and may last 4-6 hours.

Dosing and Administration

The recommended starting dose is sildenafil 50mg, taken approximately one hour before sexual activity. Dosing may be adjusted to 25mg for patients requiring lower doses or increased to 100mg for enhanced effectiveness. Patients should take a maximum of one dose per 24-hour period. Food, particularly fatty meals, may delay onset of action.

Contraindications and Precautions

Sildenafil is contraindicated in patients taking nitrates due to potentially dangerous blood pressure drops. Other contraindications include severe cardiovascular disease, recent heart attack or stroke within six months, severe liver impairment, and concurrent use of riociguat. Patients with cardiovascular risk factors require careful assessment before prescribing.

Drug Interactions

Dangerous interactions occur with nitrates and riociguat. Alpha-blockers may cause hypotension when combined with sildenafil. CYP3A4 inhibitors like ketoconazole and ritonavir can increase sildenafil levels, requiring dose adjustments. Patients should inform prescribers of all current medications.

Side Effects Profile

Common side effects include headache, facial flushing, nasal congestion, and dyspepsia. Less common but serious side effects may include sudden vision loss, prolonged erections lasting over four hours, and sudden hearing loss. Patients experiencing serious side effects should seek immediate medical attention.

Choosing Between Generic and Branded Options

EverydayMeds provides both generic sildenafil and branded Viagra containing identical active ingredients. Generic sildenafil offers cost-effective treatment while maintaining the same efficacy and safety profile. Patients can choose their preferred option during the checkout process after completing our online consultation.

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.
Couple laughing together

How it works

Achieve your goals in just a few simple steps.

Step 1

Start Free Consultation

Select safe UK treatments. Quick answers.

Step 2

Review By Our Clinical Team

Our expert team will use your consultation as the basis of our recommendation and communicate with you.

Step 3

Get it delivered fast

We’ll deliver direct to you, as quickly as tomorrow.

Frequently asked questions