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Sildenafil BNF Information: Quick Reference Guide

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Sildenafil BNF Information: Quick Reference Guide

Published on: June 03, 2026

Accessing accurate sildenafil BNF information UK is essential for safe, effective treatment of erectile dysfunction. At Cured Pharmacy, we provide comprehensive guidance aligned with British National Formulary standards, alongside UK-licensed sildenafil from £0.45 per tablet following clinical assessment by our registered prescribers.

Sildenafil BNF Classification and Mechanism

Sildenafil citrate is classified in the BNF under section 7.4.5 as a phosphodiesterase type-5 (PDE5) inhibitor indicated for erectile dysfunction in adult men [1]. The medication works by selectively inhibiting the PDE5 enzyme in the corpus cavernosum, enhancing the effects of nitric oxide released during sexual stimulation and promoting smooth muscle relaxation and increased blood flow to penile tissue.

Unlike earlier erectile dysfunction treatments, sildenafil's targeted mechanism means it only produces physiological effects in response to natural sexual arousal—it does not cause spontaneous erections [1]. This specificity has made sildenafil the most widely prescribed PDE5 inhibitor in UK clinical practice since its MHRA licensing in 1998.

The BNF notes that sildenafil's vasodilatory effects extend beyond penile tissue, which explains both its therapeutic action and the need for careful prescribing in patients with cardiovascular conditions [2].

According to current BNF guidance, the standard initial dose of sildenafil for erectile dysfunction is 50mg taken approximately one hour before sexual activity [1]. Based on individual response and tolerability, UK prescribers may adjust this to 25mg (for patients with hepatic or renal impairment, or those taking certain interacting medications) or increase to a maximum single dose of 100mg.

The BNF specifies a maximum dosing frequency of once daily, with optimal timing between 30 minutes to four hours before anticipated sexual activity [1]. Taking sildenafil with high-fat meals may delay absorption and onset of action, though this does not reduce overall efficacy.

For older patients (aged 65 and over), the BNF recommends considering a lower starting dose of 25mg due to altered pharmacokinetics, though many men in this age group tolerate standard dosing well under medical supervision [2].

Dose Adjustments for Specific Populations

The BNF provides specific dosing modifications for patients with hepatic impairment (Child-Pugh class A or B) and severe renal impairment (creatinine clearance below 30 mL/minute), both requiring an initial 25mg dose [1]. Sildenafil is contraindicated in severe hepatic impairment. Patients taking potent CYP3A4 inhibitors such as ritonavir, ketoconazole, or itraconazole should not exceed 25mg within 48 hours, as these medications significantly increase sildenafil plasma concentrations and prolong its half-life.

Contraindications and Precautions per BNF Guidance

The BNF lists several absolute contraindications for sildenafil, most critically the concurrent use of nitrate medications or nicorandil [1]. This combination can cause severe, potentially fatal hypotension due to additive vasodilatory effects. Patients must not take sildenafil within 24 hours of using any nitrate preparation, including glyceryl trinitrate sprays, isosorbide mononitrate, or recreational nitrite inhalants ('poppers').

Additional BNF contraindications include recent stroke or myocardial infarction (within 6 months), unstable angina, severe heart failure, uncontrolled hypertension or hypotension, and hereditary degenerative retinal disorders [1][2]. Sildenafil should be used with caution in patients with anatomical penile deformities (such as Peyronie's disease), conditions predisposing to priapism (sickle cell anaemia, multiple myeloma, leukaemia), and bleeding disorders.

The BNF advises particular caution when prescribing sildenafil to patients with left ventricular outflow obstruction (aortic stenosis, hypertrophic obstructive cardiomyopathy), as the vasodilatory effects may compromise cardiac output in these populations [2].

Cardiovascular Risk Assessment

Before prescribing sildenafil, UK clinicians typically perform cardiovascular risk stratification as recommended by NICE and reflected in BNF guidance [2]. Sexual activity itself carries cardiovascular demands equivalent to moderate physical exertion, and patients who cannot climb two flights of stairs without symptoms may require cardiology assessment before starting PDE5 inhibitor therapy. At Cured Pharmacy, our prescribers conduct thorough cardiovascular screening during the online consultation to ensure sildenafil is clinically appropriate for each patient.

Medication Active Ingredient Typical Dose Duration of Action Starting Price
Sildenafil Sildenafil citrate 25-100mg 4-6 hours From £0.45
Sildenafil Eropid Sildenafil citrate 50-100mg 4-6 hours From £8.99
Tadalafil Tadalafil 10-20mg Up to 36 hours From £9.99
Tadalafil (Teva) Tadalafil 10-20mg Up to 36 hours From £9.99
Viagra Connect Sildenafil citrate 50mg 4-6 hours From £11.49

Common and Serious Side Effects Listed in the BNF

The BNF documents that the most frequently reported side effects of sildenafil include headache (occurring in approximately 16% of users), flushing, dyspepsia, nasal congestion, and dizziness [1]. These effects are generally mild to moderate, transient, and related to the medication's vasodilatory mechanism. Visual disturbances—including altered colour perception (particularly blue-tinted vision), increased light sensitivity, and blurred vision—occur in about 3% of patients and typically resolve within hours.

Less common but clinically significant adverse effects documented in the BNF include priapism (prolonged erection exceeding four hours), which constitutes a medical emergency requiring immediate treatment to prevent permanent erectile tissue damage [1]. Patients should be counselled to seek urgent medical attention if an erection persists beyond four hours.

The BNF also notes rare but serious cardiovascular events, including myocardial infarction, sudden cardiac death, and stroke, though establishing causality is complex given that erectile dysfunction itself is associated with cardiovascular disease [2]. Non-arteritic anterior ischaemic optic neuropathy (NAION), a rare cause of sudden vision loss, has been reported in post-marketing surveillance, though a direct causal relationship remains unproven.

Drug Interactions Documented in the BNF

The BNF provides comprehensive guidance on sildenafil drug interactions, with the most critical involving medications that affect the cytochrome P450 3A4 enzyme system [1]. Potent CYP3A4 inhibitors—including azole antifungals (ketoconazole, itraconazole), macrolide antibiotics (erythromycin, clarithromycin), and HIV protease inhibitors (ritonavir, saquinavir)—significantly increase sildenafil plasma concentrations, necessitating dose reduction and extended dosing intervals.

Alpha-blockers used for benign prostatic hyperplasia or hypertension can interact with sildenafil to cause symptomatic hypotension [1]. The BNF recommends that patients should be stable on alpha-blocker therapy before initiating sildenafil, and that sildenafil should be started at the lowest dose (25mg) in these patients. Conversely, if adding an alpha-blocker to established sildenafil therapy, the alpha-blocker should be initiated at the lowest dose.

Other notable interactions documented in the BNF include CYP3A4 inducers (rifampicin, phenytoin, carbamazepine) which may reduce sildenafil efficacy, and other PDE5 inhibitors or erectile dysfunction treatments which should never be combined with sildenafil [2]. Grapefruit juice can moderately increase sildenafil levels and should be avoided around dosing times.

Interactions with Recreational Substances

The BNF explicitly warns against combining sildenafil with alkyl nitrites (poppers), which are metabolised to nitric oxide and can cause the same dangerous hypotensive effects as therapeutic nitrates [1]. Excessive alcohol consumption may impair erectile function and increase the risk of symptomatic hypotension when taken with sildenafil, though moderate alcohol intake (1-2 units) is generally considered acceptable.

Accessing Sildenafil Through UK Online Pharmacies

Following reclassification by the MHRA in 2017, sildenafil 50mg became available for pharmacy (P) supply in the UK under specific conditions, whilst other strengths remain prescription-only medicines (POM) [3]. At Cured Pharmacy, all sildenafil products require completion of a clinical assessment by our UK-registered prescribers, ensuring appropriate patient selection and safety screening aligned with BNF guidance.

Our online consultation takes under three minutes and covers the essential cardiovascular, medication, and contraindication checks mandated by the BNF and MHRA regulations [1][2]. Superintendent pharmacist Tarun Kumar (GPhC 2233073) oversees all clinical protocols to ensure every patient receives genuine UK-licensed sildenafil at competitive pricing from £0.45 per tablet, with discreet next-day delivery across the UK.

Transparent pricing is provided before consultation, and our clinical team will only approve sildenafil if it is safe and appropriate for your individual circumstances. All medications are sourced from licensed UK wholesalers and dispensed from our GPhC-registered pharmacy (9012511), guaranteeing authenticity and regulatory compliance.

Scientific References

  1. Joint Formulary Committee. (2024). British National Formulary (BNF) 87. London: BMJ Group and Pharmaceutical Press. Sildenafil citrate monograph, section 7.4.5. [accessed 13 August 2026]
  2. Kloner, R. A., et al. (2018). Cardiovascular Safety of Phosphodiesterase Type 5 Inhibitors After Nearly 2 Decades on the Market. Sexual Medicine Reviews, 6(4), 583-594. https://doi.org/10.1016/j.sxmr.2018.03.008 [accessed 13 August 2026]
  3. Medicines and Healthcare products Regulatory Agency. (2017). Reclassification of Viagra Connect (sildenafil 50 mg) to Pharmacy Medicine. MHRA Public Assessment Report. [accessed 13 August 2026]
  4. 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. The content reflects current BNF guidance but should not replace professional medical consultation.

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Faq

What is the BNF recommended starting dose for sildenafil?
The BNF recommends an initial dose of 50mg taken approximately one hour before sexual activity, with adjustments to 25mg or 100mg based on individual response and tolerability.
Can I take sildenafil if I'm on blood pressure medication?
It depends on the specific medication. Sildenafil is absolutely contraindicated with nitrates and requires caution with alpha-blockers, but may be suitable with other antihypertensives subject to prescriber assessment.
How long does sildenafil take to work according to BNF guidance?
The BNF states sildenafil typically takes effect within 30-60 minutes, with optimal timing around one hour before sexual activity, though high-fat meals may delay absorption.
What are the most common sildenafil side effects listed in the BNF?
The most frequent side effects documented in the BNF include headache (16% of users), flushing, dyspepsia, nasal congestion, and transient visual disturbances such as blue-tinted vision.
Is sildenafil safe for patients over 65 years old?
Yes, though the BNF recommends considering a lower starting dose of 25mg for older patients due to altered pharmacokinetics, with dose titration based on response and tolerability.
Can I take sildenafil daily according to BNF recommendations?
The BNF specifies a maximum dosing frequency of once per 24-hour period for on-demand use. Daily low-dose regimens are not standard for sildenafil in erectile dysfunction management.
What should I do if sildenafil doesn't work the first time?
The BNF notes that adequate sexual stimulation is required for sildenafil to be effective. If unsuccessful initially, try on at least 4-6 separate occasions before considering dose adjustment or alternative treatments.
Where can I buy genuine sildenafil online in the UK?
Genuine UK-licensed sildenafil is available from Cured Pharmacy from £0.45 per tablet following a free online consultation with our UK-registered prescribers, ensuring BNF-compliant prescribing and authentic medication.
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


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