How Does Viagra Work? Essential Facts

Viagra, containing sildenafil citrate, is a prescription medicine for erectile dysfunction that works by increasing blood flow to the penis during sexual arousal. As a PDE5 inhibitor, it blocks specific enzymes that restrict blood flow, helping men achieve and maintain erections when sexually stimulated. EverydayMeds offers both branded Viagra and generic sildenafil, giving patients choice between branded and more affordable generic options at checkout.

  • Blocks PDE5 enzyme to increase blood flow to the penis
  • Takes 30-60 minutes to work and effects last 4-6 hours
  • Requires sexual stimulation - does not cause automatic erections
  • Available in 25mg, 50mg, and 100mg strengths
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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 Science Behind Viagra's Effectiveness

PDE5 Inhibition Mechanism

Viagra works by inhibiting phosphodiesterase type 5 (PDE5), an enzyme found in blood vessel walls throughout the body, particularly in penile tissue. During sexual arousal, the body naturally releases nitric oxide, which increases levels of cyclic GMP - a chemical messenger that relaxes smooth muscle and dilates blood vessels. PDE5 normally breaks down cyclic GMP, but Viagra blocks this process, allowing blood vessels to remain dilated and blood flow to increase to the penis.

Timing and Duration

Most men find Viagra becomes effective within 30-60 minutes of taking a tablet, though this can vary based on individual factors and whether it's taken with food. Fatty meals may delay absorption and slow the onset of action. The effects typically last 4-6 hours, though this doesn't mean an erection lasts this duration - sexual stimulation is still required throughout this window for the medicine to be effective.

Dosage Options at EverydayMeds

EverydayMeds stocks Viagra in three strengths: 25mg, 50mg, and 100mg tablets. Most men start with 50mg, which can be adjusted up to 100mg or down to 25mg depending on effectiveness and any side effects experienced. We also offer generic sildenafil in the same strengths, providing patients with a more affordable alternative that contains the same active ingredient. Only one dose should be taken in any 24-hour period.

Clinical Assessment Requirements

Before dispensing Viagra or sildenafil, our UK-licensed prescribers conduct a thorough clinical assessment. This evaluates cardiovascular health, current medications, and medical history to ensure the treatment is safe and appropriate. Men taking nitrate medications or with certain heart conditions may not be suitable candidates due to potentially dangerous drug interactions.

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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