How Does Viagra Work? The Science Explained | Cured

Clinically Proven UK Registered Pharmacy

The Science Behind Tablet Viagra: How It Works

UK-registered clinical team
Confidential and secure
No GP visit needed
Fast and discreet delivery
Start Your Free Consultation

Takes less than 2 minutes to complete 100% online

EDNEW 20% off for new customers
Genuine Products
UK-licensed only
Fast Delivery
Next-day available
Expert Advice
UK pharmacists
Man using Cured Pharmacy online consultation for erectile dysfunction treatment
From £0.45 Starting dose — clinically approved
LIVE PRICING

Our Pricing

Pricing Disclaimer: Prices on some pages may not be up to date — the live pricing table below and pricing shown during consultation are official current prices and take precedence over any other figures on the site.

Sildenafil - UK-licensed prescription Treatment
Treatment

Sildenafil

From £0.45

Future orders save 5%
Start Assessment
Tadalafil - UK-licensed prescription Treatment
Treatment

Tadalafil

From £9.99

Future orders save 5%
Start Assessment
Sildenafil Eropid - UK-licensed prescription Treatment
Treatment

Sildenafil Eropid

From £8.99

Future orders save 5%
Start Assessment
Tadalafil (Teva) - UK-licensed prescription Treatment
Treatment

Tadalafil (Teva)

From £9.99

Future orders save 5%
Start Assessment
Avarante Tablets Tadalafil Tablets 10mg - UK-licensed prescription Treatment
Treatment

Avarante Tablets Tadalafil Tablets 10mg

From £11.49

Future orders save 5%
Start Assessment
Viagra Connect 50mg - UK-licensed prescription Treatment
Treatment

Viagra Connect 50mg

From £11.49

Future orders save 5%
Start Assessment

The Science Behind Tablet Viagra: How It Works

Published on: June 03, 2026

Understanding how does viagra work in the body helps you make informed decisions about erectile dysfunction treatment. Viagra (sildenafil citrate) works by inhibiting a specific enzyme called phosphodiesterase type 5 (PDE5), which increases blood flow to the penis during sexual stimulation—a mechanism supported by over 25 years of clinical evidence [1].

The Biological Mechanism: How Does Viagra Work at a Cellular Level?

When sexual arousal occurs, nerve signals trigger the release of nitric oxide (NO) in the erectile tissue of the penis. This nitric oxide activates an enzyme called guanylate cyclase, which produces cyclic guanosine monophosphate (cGMP)—a chemical messenger that relaxes smooth muscle cells in the blood vessel walls [1]. As these muscles relax, blood vessels dilate and fill the corpora cavernosa (the spongy erectile chambers), creating an erection.

Under normal circumstances, another enzyme called phosphodiesterase type 5 (PDE5) breaks down cGMP, ending the erection. Sildenafil—the active ingredient in Viagra—selectively inhibits PDE5, preventing the breakdown of cGMP and allowing it to accumulate [2]. This prolonged presence of cGMP maintains smooth muscle relaxation and sustained blood flow, making it easier to achieve and maintain an erection when sexually stimulated.

Critically, Viagra does not cause automatic erections. Sexual stimulation is still required to trigger the initial nitric oxide release. Sildenafil simply enhances the body's natural erectile response by preserving the cGMP that sexual arousal produces [1][2].

How Long Does Viagra Take to Work and How Long Does It Last?

Sildenafil is rapidly absorbed after oral administration, with peak plasma concentrations typically reached 30 to 120 minutes after dosing [3]. In clinical practice, most men find Viagra begins working within 30 to 60 minutes when taken on an empty stomach. High-fat meals can delay absorption by up to an hour, so taking sildenafil at least two hours after eating may optimise onset time.

The therapeutic effect of a single 50mg or 100mg dose typically lasts four to five hours, though this varies between individuals [3]. During this window, sildenafil remains active in your system, making it easier to achieve erections with sexual stimulation. Some men report residual effects up to eight hours post-dose, but effectiveness generally diminishes after the five-hour mark.

It's important to note that Viagra does not provide continuous erections for four hours—it simply enables your body to respond normally to sexual arousal during that period. After ejaculation, the natural refractory period still applies, though some men find they can achieve subsequent erections more easily while sildenafil remains active.

Factors That Influence Onset and Duration

Age, liver function, kidney function, and concurrent medications all affect how quickly sildenafil is metabolised. Older adults and those with hepatic or renal impairment may experience longer-lasting effects and should discuss appropriate dosing with their prescriber [3]. Alcohol consumption can also reduce effectiveness by impairing the erectile response independently of sildenafil's mechanism.

Viagra vs Tadalafil: Comparing PDE5 Inhibitor Mechanisms

Both sildenafil (Viagra) and tadalafil (Cialis) are PDE5 inhibitors that work through the same fundamental mechanism—blocking the enzyme that breaks down cGMP. However, their pharmacokinetic profiles differ significantly, affecting how they're used in clinical practice.

Tadalafil has a much longer half-life of approximately 17.5 hours compared to sildenafil's 3 to 5 hours [4]. This extended duration means tadalafil can remain effective for up to 36 hours after a single dose, offering greater spontaneity. Some men prefer daily low-dose tadalafil (2.5mg or 5mg) to maintain continuous readiness, while others favour sildenafil's shorter, more predictable window for planned sexual activity.

Both medications require sexual stimulation to work and have comparable efficacy rates—clinical trials show approximately 70-85% of men with erectile dysfunction respond to either treatment [1][4]. The choice between them often comes down to lifestyle preference: sildenafil for on-demand use with faster onset, or tadalafil for extended duration and potential daily dosing.

Active Ingredient Brand Examples Onset Time Duration Starting Price
Sildenafil Viagra, Sildenafil 30-60 minutes 4-5 hours From £0.45
Tadalafil Cialis, Tadalafil 30-60 minutes Up to 36 hours From £9.99
Sildenafil (Eropid) Eropid 30-60 minutes 4-5 hours From £8.99
Tadalafil (Teva) Teva brand 30-60 minutes Up to 36 hours From £9.99

Does Viagra Work for Everyone? Understanding Response Rates

In randomised controlled trials, sildenafil demonstrated significant improvement in erectile function in 70-84% of men across various causes of erectile dysfunction, including diabetes, cardiovascular disease, and psychological factors [1][2]. However, response rates vary depending on the underlying cause and severity of ED.

Men with psychogenic erectile dysfunction (caused by anxiety, stress, or psychological factors) generally show higher response rates than those with severe vascular disease or nerve damage from radical prostatectomy [2]. Diabetes-related ED typically shows moderate response rates, with approximately 60% of men achieving erections sufficient for intercourse.

Non-responders—men who don't achieve adequate results with sildenafil—may benefit from dose optimisation, switching to tadalafil, or addressing underlying cardiovascular risk factors. Our clinical team at Cured Pharmacy can review your response and suggest alternative treatments if initial therapy proves insufficient. All erectile dysfunction medications require assessment by a UK-registered prescriber to ensure suitability and safety.

Why Some Men Don't Respond to Viagra

Inadequate sexual stimulation, incorrect timing (taking sildenafil too close to a high-fat meal), psychological barriers, severe vascular disease, or very low testosterone levels can all reduce sildenafil's effectiveness. Concurrent use of nitrates (commonly prescribed for angina) is an absolute contraindication due to the risk of severe hypotension [3]. Your prescriber will assess these factors during consultation.

Common Side Effects and How Viagra's Mechanism Explains Them

The most frequently reported side effects of sildenafil—headache (16% of users), flushing (10%), and nasal congestion (4%)—are directly related to its mechanism of action [3]. Because PDE5 is also present in blood vessels throughout the body (not just the penis), sildenafil causes mild vasodilation in other tissues, leading to these predictable effects.

Visual disturbances, including a blue tinge to vision or increased light sensitivity, occur in approximately 3% of men taking higher doses [3]. This happens because sildenafil has weak activity against PDE6, an enzyme found in the retina. These visual effects are temporary and resolve as the medication is metabolised.

Serious side effects are rare but include priapism (erection lasting more than four hours), sudden vision loss, and sudden hearing loss. These require immediate medical attention. The risk of cardiovascular events is not increased in men without pre-existing heart conditions, but sildenafil should not be used by men taking nitrate medications or those with recent stroke, heart attack, or severe heart failure [3].

Accessing Viagra and Sildenafil Through UK Online Pharmacies

Sildenafil is available in the UK both as a prescription-only medicine (POM) and, in the 50mg strength under the brand Viagra Connect, as a pharmacy medicine for men over 18. At Cured Pharmacy, we offer genuine UK-licensed sildenafil from £0.45 per tablet, with transparent upfront pricing and a free online consultation completed in under three minutes.

All erectile dysfunction treatments dispensed by Cured Pharmacy require clinical assessment by our UK-registered prescribers to ensure safety and suitability. Our superintendent pharmacist, Tarun Kumar (GPhC 2233073), oversees all clinical protocols, and we're regulated by the General Pharmaceutical Council (GPhC Registration Number 9012511).

We stock both branded Viagra Connect and generic sildenafil in 25mg, 50mg, and 100mg strengths, as well as alternative PDE5 inhibitors including tadalafil. Your prescriber will recommend the most appropriate treatment based on your medical history, current medications, and individual response. Discreet packaging and next-day delivery are standard across all orders.

Starting Your Assessment at Cured Pharmacy

Begin with our confidential online questionnaire, which takes less than three minutes to complete. A UK prescriber will review your answers, and if sildenafil is suitable, we'll dispense your medication for next-day delivery. If you have questions about how Viagra works or which ED treatment is right for you, our clinical team is available on (+44) 116 4646009.

Scientific References

  1. Goldstein, I., Lue, T. F., Padma-Nathan, H., Rosen, R. C., Steers, W. D., & Wicker, P. A. (1998). Oral sildenafil in the treatment of erectile dysfunction. New England Journal of Medicine, 338(20), 1397–1404. https://doi.org/10.1056/NEJM199805143382001 [accessed 13 August 2026]
  2. Boolell, M., Allen, M. J., Ballard, S. A., Gepi-Attee, S., Muirhead, G. J., Naylor, A. M., Osterloh, I. H., & Gingell, C. (1996). Sildenafil: an orally active type 5 cyclic GMP-specific phosphodiesterase inhibitor for the treatment of penile erectile dysfunction. International Journal of Impotence Research, 8(2), 47–52. [accessed 13 August 2026]
  3. Medicines and Healthcare products Regulatory Agency (MHRA). (2023). Sildenafil 50mg film-coated tablets - Summary of Product Characteristics (SmPC). Electronic Medicines Compendium. https://www.medicines.org.uk/emc/product/9533/smpc [accessed 13 August 2026]
  4. Carson, C. C., & Lue, T. F. (2005). Phosphodiesterase type 5 inhibitors for erectile dysfunction. BJU International, 96(3), 257–280. https://doi.org/10.1111/j.1464-410X.2005.05614.x [accessed 13 August 2026]
  5. NHS. (2026). Erectile dysfunction (impotence). https://www.nhs.uk/conditions/erection-problems-erectile-dysfunction/ Accessed 13 August 2026.

Information on this page is for educational purposes only and is not medical advice. All prescription treatments require clinical assessment by a UK-registered prescriber. Always consult a qualified healthcare professional before starting any new medication.

Trusted by thousands

Real people, real results

Jane L.

"Brilliant. Lost 4 stone on mounjaro no side effects at all. Cured pharmacy are excellent. Always helpful pens sent out quickly always comes with needles and sterile wipes. If you want to go on GLP-1 go to cured pharmacy. So professional. Thank you cured pharmacy you changed my health and well being."

Ann-Marie

"I absolutely love this product, I have been using 2.5mg as maintenance dose and have managed to control my weight without any side effects and can still eat well balanced meals. The pharmacy is very efficient friendly and helpful I would not purchase from anywhere else."

Sacha W.

"So far I'm really impressed by my results it's crazy cause I'm not snacking like how I used to do and I see my face slimming down already and it's only been 2 and a half weeks. Can't wait to give my feedback in 5 months time thank you cured pharmacy."

Kimberly G.

"Mounjaro has corrected my hormonal weight gain during menopause. I am using it now to maintain that balance. The results for me have been exceptional!"

Jennifer

"Great really helps cure those nasty habits can't wait for my next mounjaro pen."

How it Works?

Select from our recommended UK-licensed medications.

1

Choose your treatment

Step 1: Choose your treatment from Cured Pharmacy

Select safe UK treatments. Quick answers.

2

Answer quick questions

Step 2: Answer quick consultation questions

We will deliver direct to you as quickly as tomorrow.

3

Get it delivered fast

Step 3: Fast discreet delivery to your door

Start Your Assessment For Erectile Dysfunction

Start your journey to better health today.

  • Reviewed by UK-based prescribers
  • Takes under 3 minutes
  • Discreet Packaging

Start Your Journey To Better Health Today

Once you complete a short online assessment you will be able to choose your preferred treatment from safe medically approved options tailored to you.

Start My Assessment

Returning Customer?

Log in to Your Account

Faq

How does Viagra work in the body to produce an erection?
Viagra (sildenafil) inhibits the PDE5 enzyme, which normally breaks down cGMP—a chemical messenger that relaxes blood vessels in the penis. By preserving cGMP levels during sexual arousal, sildenafil increases blood flow to erectile tissue, making erections easier to achieve and maintain.
Does Viagra work without sexual stimulation?
No. Viagra enhances your body's natural response to sexual arousal but does not cause automatic erections. Sexual stimulation is required to trigger the release of nitric oxide, which initiates the cascade that sildenafil amplifies.
How long does it take for Viagra to start working?
Most men experience effects within 30 to 60 minutes when taken on an empty stomach. High-fat meals can delay onset by up to an hour, so taking sildenafil at least two hours after eating may optimise timing.
How long does Viagra's effect last in your system?
A single dose of sildenafil typically remains effective for four to five hours, though some men report residual effects up to eight hours. During this window, you can achieve erections with sexual stimulation, but effectiveness gradually diminishes.
Why does Viagra cause headaches and flushing?
These side effects result from mild vasodilation (widening of blood vessels) throughout the body, not just in the penis. Because PDE5 is present in other tissues, sildenafil's mechanism causes temporary headaches in about 16% of users and flushing in 10%.
Is the mechanism of Viagra different from tadalafil (Cialis)?
Both are PDE5 inhibitors working through the same fundamental mechanism—blocking cGMP breakdown to enhance blood flow. The key difference is duration: tadalafil lasts up to 36 hours versus sildenafil's 4-5 hours, due to different pharmacokinetic profiles.
Does Viagra work for everyone with erectile dysfunction?
Clinical trials show sildenafil improves erectile function in 70-84% of men, but response rates vary based on the underlying cause. Men with psychogenic ED typically respond better than those with severe vascular damage or nerve injury.
Can I buy sildenafil online in the UK without seeing a doctor?
Sildenafil requires a clinical assessment by a UK-registered prescriber, which can be completed online through a confidential questionnaire at Cured Pharmacy. Our team reviews your medical history to ensure safety before dispensing, with approval typically granted within hours.
How much does Viagra cost at Cured Pharmacy?
Viagra prices at Cured Pharmacy vary depending on dosage and quantity, with competitive rates for both branded and generic sildenafil options. Our online consultation is completely free, and we offer transparent pricing with no hidden fees. Visit our website to view current prices and available treatment packs.
Is Viagra available without a prescription in the UK?
No, Viagra requires a prescription in the UK as it is a prescription-only medicine. At Cured Pharmacy, our registered clinicians can provide a free online consultation and issue a prescription if suitable, making the process quick and convenient. This ensures your safety and that Viagra is appropriate for your individual health needs.
How quickly can I get Viagra delivered from Cured Pharmacy?
Cured Pharmacy offers fast, discreet delivery across the UK, with next-day delivery options available for orders placed before our cut-off time. All Viagra orders are sent in plain, unmarked packaging to protect your privacy. Standard delivery typically takes 2-3 working days.
Is Viagra safe to use long term for erectile dysfunction?
Yes, Viagra is generally safe for long-term use when taken as prescribed and under medical supervision. Our clinicians at Cured Pharmacy regularly review your treatment to ensure it remains suitable and effective. It's important to report any side effects or health changes during ongoing use.
What is the difference between Viagra and generic sildenafil?
Viagra is the branded version containing sildenafil citrate, while generic sildenafil contains the same active ingredient and works identically in the body. The main difference is price, with generic versions being significantly more affordable. Cured Pharmacy offers both options, allowing you to choose based on your preference and budget.
Tarun Kumar, Prescribing Pharmacist

Medically reviewed by

Tarun Kumar, Prescribing Pharmacist (GPhC 2233073)

Reviewed on: June 03, 2026

Last reviewed: 13 August 2026

Last updated on 13 August 2026.

Review History

Our experts continually monitor new findings in health and medicine, and we update our articles when new information becomes available.

Why this page was updated on 13 August 2026

Content checked and updated as part of our periodic review, to ensure accuracy and currentness.

Current version (13 August 2026)

Edited by: The Editorial Team

Medically reviewed by:

Tarun Kumar, GPhC No. 2233073, Prescribing Pharmacist


How we source info.

When we present you with stats, data, opinion or a consensus, we'll tell you where this came from.