How Sildenafil Works: Complete BNF Treatment Guide

Sildenafil, listed in the British National Formulary (BNF), is a proven PDE5 inhibitor used to treat erectile dysfunction. Understanding how this medication works in your body can help you make informed decisions about ED treatment. EverydayMeds offers both branded Viagra and generic sildenafil, allowing you to choose the option that best suits your needs and budget while receiving the same effective active ingredient.

  • Blocks PDE5 enzyme to improve blood flow to the penis
  • Requires sexual arousal to work effectively
  • Takes 30-60 minutes to become active in your system
  • Effects may last 4-6 hours but don't cause prolonged erections
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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 Sildenafil's Mechanism of Action

What Is Sildenafil and How Does It Work?

Sildenafil belongs to a class of medications called phosphodiesterase type 5 (PDE5) inhibitors, as detailed in the BNF. When you become sexually aroused, your body naturally releases nitric oxide in the penis. This chemical triggers the production of cyclic guanosine monophosphate (cGMP), which relaxes smooth muscles in blood vessels and allows increased blood flow to the penis.

The PDE5 enzyme typically breaks down cGMP, reducing blood flow. Sildenafil works by blocking this PDE5 enzyme, allowing cGMP levels to remain elevated and maintaining improved blood flow during sexual arousal. This mechanism helps men achieve and maintain erections suitable for sexual activity.

Timeline: When Sildenafil Starts Working

Most men find sildenafil becomes effective within 30-60 minutes of taking the tablet. The medication reaches peak blood levels approximately 60 minutes after oral administration. However, individual response times can vary based on factors such as age, metabolism, food intake, and overall health status.

Taking sildenafil on an empty stomach may result in faster absorption, whilst fatty meals can delay the onset of action by up to an hour. The effects typically last between 4-6 hours, though this doesn't mean you'll have an erection for this entire period - sexual stimulation is still required throughout.

Dosage Information According to BNF Guidelines

The BNF recommends starting with sildenafil 50mg, taken approximately one hour before sexual activity. Based on effectiveness and tolerability, your prescriber may adjust this to 25mg or increase to 100mg. The maximum recommended dose is 100mg, and you should never take more than one dose in a 24-hour period.

EverydayMeds offers both branded Viagra and generic sildenafil in all standard strengths (25mg, 50mg, and 100mg). Both formulations contain the same active ingredient and work identically - the choice between branded and generic often comes down to personal preference and cost considerations.

Important Considerations for Safe Use

Sildenafil requires sexual arousal to work effectively - it won't cause automatic erections. The medication enhances your body's natural response to sexual stimulation rather than replacing it. This is an important distinction that helps ensure the medication works as intended.

Before starting sildenafil treatment, you'll need to complete a clinical assessment with a UK-licensed prescriber. This evaluation ensures the medication is suitable for your individual health profile and doesn't interact with other medications you may be taking.

Who Can Use Sildenafil?

Sildenafil is suitable for adult men experiencing erectile dysfunction. However, it's not appropriate for everyone. Men taking nitrate medications (such as GTN spray), those with severe heart conditions, or individuals with certain other health conditions may not be suitable candidates for sildenafil treatment.

Your online consultation will assess your medical history, current medications, and overall cardiovascular health to determine if sildenafil is safe and appropriate for you. This thorough assessment process helps ensure you receive treatment that's both effective and safe.

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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