How Does Viagra Work? The Science Behind Sildenafil

Viagra contains sildenafil citrate, a PDE5 inhibitor that helps treat erectile dysfunction by increasing blood flow to the penis during sexual arousal. Understanding how this medication works can help you make informed decisions about your treatment options. 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 active ingredient.

  • Blocks PDE5 enzyme to improve blood flow to the penis
  • Requires sexual stimulation 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.

The Pharmacology of Sildenafil: What Happens in Your Body

Understanding PDE5 and How Sildenafil Works

Viagra's active ingredient, sildenafil citrate, belongs to a class of medications called phosphodiesterase type 5 (PDE5) inhibitors. To understand how it works, it's helpful to know what happens naturally during sexual arousal. When a man becomes sexually stimulated, nerve signals trigger the release of nitric oxide in the penis, which increases levels of a chemical called cyclic guanosine monophosphate (cGMP). This chemical causes the smooth muscles in blood vessels to relax, allowing increased blood flow into the penis and creating an erection.

How PDE5 Normally Affects Erections

Under normal circumstances, the enzyme PDE5 breaks down cGMP, which naturally causes the erection to subside. However, men with erectile dysfunction may have overactive PDE5 or insufficient blood flow, making it difficult to achieve or maintain an erection. Sildenafil works by selectively blocking PDE5, which allows cGMP levels to remain elevated for longer periods, promoting better blood flow to the penis when sexually aroused.

Timing and Duration of Effects

Sildenafil typically begins working within 30 to 60 minutes of taking the tablet, though this can vary depending on individual factors such as age, overall health, and whether it's taken with food. Fatty meals may delay absorption and slow the onset of action. The medication's effects can last approximately 4 to 6 hours, but this doesn't mean you'll have an erection for this entire duration. Sexual stimulation is still required for the medication to work effectively.

Available Dosages and Treatment Options

Both Viagra and generic sildenafil are available in three strengths: 25mg, 50mg, and 100mg tablets. Most men start with a 50mg dose, which can be adjusted based on effectiveness and tolerability. Your prescriber may recommend a lower 25mg dose if you experience side effects, or increase to 100mg if the initial dose isn't sufficiently effective. It's important to take only one dose within any 24-hour period.

Choosing Between Viagra and Sildenafil

At EverydayMeds, we offer both branded Viagra and generic sildenafil options. Both contain the same active ingredient and work identically in your body. The main differences are price and packaging - generic sildenafil typically costs significantly less than branded Viagra while providing the same therapeutic benefits. This choice allows you to select the option that best fits your budget and preferences during the checkout process.

Safety Considerations and Contraindications

Sildenafil is generally well-tolerated, but it's not suitable for everyone. The medication can cause a temporary drop in blood pressure, which is usually mild but can be dangerous when combined with certain medications, particularly nitrates used for chest pain. Men taking GTN spray, isosorbide medications, or certain blood pressure treatments should not use sildenafil. Additionally, those with severe heart conditions, recent heart attacks or strokes, or severe liver problems may not be suitable candidates for this treatment.

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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