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What is Viagra? Essential Information Guide

Published on: June 03, 2026

Understanding what is viagra and how does it work uk is essential for men considering treatment for erectile dysfunction. Viagra is the brand name for sildenafil citrate, a prescription medication licensed by the MHRA that helps men achieve and maintain erections by increasing blood flow to the penis during sexual stimulation. At Cured Pharmacy, UK-registered prescribers assess your suitability through a free online consultation, with genuine sildenafil available from £0.45 per tablet.

How Viagra Works: The Science Behind Sildenafil

Viagra contains sildenafil citrate, a phosphodiesterase type 5 (PDE5) inhibitor that works by blocking the enzyme responsible for breaking down cyclic guanosine monophosphate (cGMP) in the smooth muscle cells lining blood vessels of the penis [1]. When sexually aroused, your body naturally releases nitric oxide, which triggers cGMP production. By preventing PDE5 from degrading cGMP, sildenafil allows blood vessels to remain dilated for longer, facilitating increased blood flow to the erectile tissue.

Clinical trials demonstrate that sildenafil significantly improves erectile function across all severities of erectile dysfunction, with approximately 74% of men reporting improved erections at the 100mg dose compared to 25% on placebo [2]. The medication does not cause automatic erections—sexual stimulation is required to trigger the natural biochemical cascade that sildenafil then amplifies.

Sildenafil begins working within 30-60 minutes of ingestion, with peak plasma concentrations reached around one hour after administration [1]. The effects typically last 4-6 hours, though this varies based on individual metabolism, age, and whether the tablet is taken with food. High-fat meals can delay absorption by up to 60 minutes, so taking Viagra on an empty stomach optimises onset time.

Viagra vs Sildenafil: Understanding the Difference

Viagra is the original branded product manufactured by Pfizer, while sildenafil refers to the generic unbranded version containing the identical active ingredient at the same therapeutic doses. Both formulations are bioequivalent—meaning they work identically in the body—and are subject to the same rigorous MHRA licensing standards for safety, quality, and efficacy [3].

The primary difference lies in cost. Generic sildenafil became widely available in the UK after Pfizer's patent expired in 2013, creating significant price competition. At Cured Pharmacy, generic sildenafil starts from £0.45 per tablet, offering substantial savings whilst delivering the same clinical outcomes as the branded alternative.

Some patients report preferential response to one formulation over another, though clinical evidence does not support meaningful therapeutic differences. Your UK prescriber will recommend the most cost-effective option based on your medical history and preferences during your online consultation.

Which Formulation Should You Choose?

For most men, generic sildenafil represents the optimal choice, combining proven efficacy with significantly lower cost. Branded Viagra may be preferred by patients who value brand recognition or have established successful treatment with the original formulation. Both require the same clinical assessment process and are dispensed following approval by a UK-registered prescriber at Cured Pharmacy.

What is Viagra Used For? Approved Indications in the UK

Viagra is licensed in the UK exclusively for the treatment of erectile dysfunction (ED) in adult men—defined as the persistent inability to achieve or maintain an erection sufficient for satisfactory sexual performance [2]. The MHRA has approved sildenafil for ED across all severity levels, from mild occasional difficulty to complete inability to achieve erections.

Erectile dysfunction affects approximately 4.3 million men in the UK, with prevalence increasing with age—around 40% of men aged 40 and 70% of men aged 70 experience some degree of ED [4]. Common underlying causes include cardiovascular disease, diabetes, hypertension, obesity, psychological factors, and medication side effects. Sildenafil treats the symptom rather than the underlying cause, making it essential to address contributory health conditions alongside pharmacological treatment.

Sildenafil is also licensed under different brand names for pulmonary arterial hypertension at different doses, but Viagra specifically refers to the erectile dysfunction formulation. Off-label use for other conditions is not recommended without specialist guidance.

Who Can Safely Use Viagra?

Viagra is suitable for most men with erectile dysfunction, but contraindications include concurrent use of nitrate medications (used for angina), severe cardiovascular disease, recent stroke or heart attack, uncontrolled hypertension, and certain rare inherited eye conditions [1]. Your Cured Pharmacy prescriber will assess your full medical history, current medications, and cardiovascular risk factors during your online consultation to ensure sildenafil is safe and appropriate for you.

Viagra Dosage: Finding the Right Strength

Viagra is available in three doses in the UK: 25mg, 50mg, and 100mg tablets. The recommended starting dose for most men is 50mg, taken approximately one hour before anticipated sexual activity [1]. Based on efficacy and tolerability, your prescriber may adjust the dose upward to 100mg for enhanced effect or downward to 25mg if you experience side effects.

The maximum recommended dosing frequency is once per 24-hour period. Taking higher doses or more frequent doses does not improve outcomes and significantly increases the risk of adverse effects. Clinical trials show dose-dependent improvements in erectile function, with 100mg producing the highest response rates but also the greatest incidence of side effects [2].

Older men, those with hepatic or renal impairment, and patients taking certain CYP3A4 inhibitors (such as erythromycin or ketoconazole) typically require dose reduction to 25mg initially. Your UK prescriber will determine the optimal starting dose based on your individual medical profile during your assessment at Cured Pharmacy.

Viagra Side Effects: What to Expect

The most common side effects of Viagra include headache (occurring in approximately 16% of users), facial flushing (10%), dyspepsia or indigestion (7%), nasal congestion (4%), and visual disturbances such as mild blue-tinted vision or increased light sensitivity (3%) [2]. These effects are generally mild to moderate, transient, and resolve without intervention as the medication clears from your system.

Less common but more serious adverse effects include sudden vision loss (non-arteritic anterior ischaemic optic neuropathy), sudden hearing loss, priapism (erection lasting more than 4 hours), and cardiovascular events in predisposed individuals [1]. Priapism requires immediate medical attention to prevent permanent erectile tissue damage. If you experience chest pain during sexual activity after taking Viagra, stop immediately and seek urgent medical care—do not take nitrate medications.

Drug interactions represent an important safety consideration. Sildenafil is metabolised primarily by the hepatic CYP3A4 enzyme system, meaning medications that inhibit this pathway (including certain antibiotics, antifungals, and HIV protease inhibitors) can increase sildenafil levels and side effect risk [3]. Alpha-blockers used for prostate enlargement can cause additive blood pressure lowering when combined with sildenafil, requiring dose adjustment and careful monitoring.

Managing Common Side Effects

Headaches often respond to standard over-the-counter analgesics like paracetamol. Facial flushing and nasal congestion typically diminish with continued use as your body adapts. If side effects persist or become bothersome, consult your prescriber about dose reduction or alternative treatments such as tadalafil, which has a different pharmacokinetic profile and may be better tolerated.

How to Buy Viagra Safely Online in the UK

Purchasing Viagra safely online requires using a registered UK pharmacy operating under General Pharmaceutical Council (GPhC) regulation. Cured Pharmacy is fully registered (GPhC 9012511) with superintendent pharmacist Tarun Kumar (GPhC 2233073) overseeing all clinical services. All prescription medications, including sildenafil, require completion of an online medical questionnaire reviewed by a UK-registered prescriber before dispensing.

Beware of websites offering Viagra without prescription, advertising suspiciously low prices, or operating from outside the UK. The Medicines and Healthcare products Regulatory Agency (MHRA) estimates that up to 62% of erectile dysfunction medicines purchased from unregulated online sources are counterfeit, containing incorrect doses, dangerous contaminants, or no active ingredient whatsoever [4]. Counterfeit medications pose serious health risks and offer no therapeutic benefit.

At Cured Pharmacy, your clinical assessment takes under three minutes and is reviewed by UK prescribers who can approve, decline, or request additional information based on your medical suitability. Once approved, your medication is dispensed from our UK-registered pharmacy with discreet packaging and delivery options. Transparent pricing is displayed upfront—generic sildenafil from £0.45—with no hidden fees or subscription requirements.

What to Look for in a Legitimate UK Pharmacy

Verify the pharmacy displays a GPhC registration number prominently on their website. Check the GPhC register directly at pharmacyregulation.org to confirm legitimacy. Legitimate pharmacies always require a clinical consultation before prescribing, display clear contact information including a UK telephone number, and source medications exclusively from licensed UK wholesalers. The website should feature the GPhC internet pharmacy logo, which links to the official register when clicked.

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. Eardley, I., Ellis, P., Boolell, M., & Wulff, M. (2002). Efficacy and safety of sildenafil citrate in the treatment of men with mild to moderate erectile dysfunction. British Journal of Psychiatry, 181(3), 271–272. https://doi.org/10.1192/bjp.181.3.271 [accessed 13 August 2026]
3. Nichols, D. J., Muirhead, G. J., & Harness, J. A. (2002). Pharmacokinetics of sildenafil after single oral doses in healthy male subjects: absolute bioavailability, food effects and dose proportionality. British Journal of Clinical Pharmacology, 53(Suppl 1), 5S–12S. https://doi.org/10.1046/j.0306-5251.2001.00027.x [accessed 13 August 2026]
4. Medicines and Healthcare products Regulatory Agency. (2017). Falsified medical products strategy 2017–2021. GOV.UK. https://www.gov.uk/government/publications/falsified-medical-products-strategy [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.