What'S Sildenafil Citrate? - Guide | Cured Pharmacy

What'S Sildenafil Citrate?

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Tarun Kumar, Prescribing Pharmacist at Cured Pharmacy

Medically reviewed by

Tarun Kumar, Prescribing Pharmacist (GPhC 2233073)

Reviewed on: 17 June 2026

Last Updated: 12 August 2026

If you have ever typed what's sildenafil citrate into a search engine at 2am, you are certainly not alone. Millions of men across the UK are quietly trying to understand the medication their doctor has mentioned, or the one they spotted on a pharmacy shelf after Viagra became available over the counter. Sildenafil citrate is the active ingredient behind one of the most widely recognised treatments for erectile dysfunction in the world, and yet for many people its name still carries confusion, uncertainty, or even a little stigma. This guide cuts through all of that in plain, honest language.

Quick Summary

Sildenafil citrate is a prescription-grade medicine that treats erectile dysfunction by improving blood flow to the penis during sexual arousal. It belongs to a class of drugs called PDE5 inhibitors and has been safely used by men in the UK for over two decades.

  • Sildenafil citrate works by blocking the PDE5 enzyme, allowing blood vessels in the penis to relax and fill with blood
  • The standard starting dose is 50mg, taken 30 to 60 minutes before sexual activity
  • It does not cause an erection on its own — sexual stimulation is still required
  • Common side effects include flushing, headache, and mild nasal congestion
  • It must not be taken with nitrate-based medicines due to a dangerous drop in blood pressure

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Table of Contents

  1. What's Sildenafil Citrate and Where Does It Come From?
  2. How Sildenafil Citrate Works in the Body
  3. Doses, Formulations and How to Take It Correctly
  4. Side Effects and Who Should Avoid Sildenafil Citrate
  5. Sildenafil Citrate vs Other ED Treatments
  6. How and Where to Buy Sildenafil Citrate Safely in the UK
  7. Key Takeaways
  8. When to Seek Professional Advice
  9. Scientific References
  10. FAQs

What's Sildenafil Citrate and Where Does It Come From?

Understanding what's sildenafil citrate begins with a rather unexpected story. In the late 1980s, researchers at Pfizer were developing a compound to treat angina and high blood pressure. The drug they were testing, originally coded UK-92,480, was not particularly effective for the heart. However, the clinical trial participants reported a notable and consistent side effect — significantly improved erections. By 1998, Pfizer launched the compound commercially under the brand name Viagra, and the world of men's health changed almost overnight.

Sildenafil citrate is the salt form of sildenafil, which simply means it has been combined with citric acid to improve its stability and solubility for use in tablets. The "citrate" part does not add any therapeutic effect — it is purely a pharmaceutical formulation technique. The active component doing all the work is sildenafil itself. When Pfizer's patent on Viagra expired in the UK in 2013, a wave of generic sildenafil citrate products became legally available, dramatically reducing the cost for patients.

Today, sildenafil citrate is available in several branded and unbranded forms including Sildenafil (Teva), Viagra (Sildenafil), and Viagra Connect generic form (Sildenafil). The active ingredient is identical across all formulations — only the brand name and price differ. This is genuinely good news for anyone who has previously found the branded version too costly.

  • Originally developed as a cardiovascular drug in the 1980s
  • Launched as Viagra by Pfizer in 1998 for erectile dysfunction
  • The "citrate" suffix refers to its salt formulation, not an additional ingredient
  • Generic versions became available in the UK from 2013 onwards
  • Now one of the most dispensed medications in the UK primary care setting

How Sildenafil Citrate Works in the Body

To properly answer what's sildenafil citrate, you need to understand the physiology of an erection. When a man becomes sexually aroused, the nervous system releases nitric oxide (NO) into the smooth muscle cells lining the blood vessels of the penis. Nitric oxide activates an enzyme called guanylate cyclase, which produces a molecule called cyclic guanosine monophosphate (cGMP). cGMP relaxes the smooth muscle walls of penile arteries, allowing them to dilate and fill with blood, which produces an erection.

The problem for many men with erectile dysfunction is that another enzyme, called phosphodiesterase type 5 (PDE5), breaks down cGMP before it can do its job properly. This is where what's sildenafil citrate becomes clinically important. Sildenafil citrate is a selective PDE5 inhibitor — it blocks this enzyme, allowing cGMP to accumulate, the blood vessels to stay dilated, and the erection to develop and be maintained.

A critical point that is often misunderstood: sildenafil citrate does not produce an erection on its own. Sexual stimulation is still required to trigger the initial release of nitric oxide. The drug simply makes the downstream process more effective. This is why it does not work if you simply take a tablet and sit on the sofa — arousal must come first. In 2026, this remains one of the most commonly asked clarifications in pharmacy consultations.

  • Sildenafil citrate selectively inhibits the PDE5 enzyme in penile tissue
  • This allows cGMP levels to rise, relaxing smooth muscle and increasing blood flow
  • Sexual stimulation is required — the drug amplifies the natural arousal response
  • Effects typically begin within 30 to 60 minutes of taking the tablet
  • Duration of action is approximately four to six hours

Doses, Formulations and How to Take It Correctly

One reason men struggle with sildenafil citrate is taking it incorrectly and then concluding it "doesn't work." Getting the timing and conditions right makes a substantial difference to how well the medication performs. Knowing what's sildenafil citrate also means knowing how to use it properly for the best possible outcome.

Sildenafil citrate is available in three standard doses: 25mg, 50mg, and 100mg. The 25mg dose is typically used for older men or those with kidney and liver concerns. The 50mg dose is the standard starting point for most adults and represents the most commonly prescribed strength. If 50mg is well tolerated but not fully effective after several attempts, a prescriber may recommend increasing to 100mg, which is the maximum single dose permitted. The Sildenafil 50mg tablet is one of the most frequently dispensed strengths in UK pharmacies.

For best results, take the tablet on an empty stomach or after a light meal. A large, fatty meal — such as a takeaway — can significantly delay absorption and reduce peak plasma concentration by up to 29%, according to the electronic Medicines Compendium. Alcohol should be kept to a minimum, as it can worsen erectile function independently and also exacerbates the blood-pressure-lowering effect of sildenafil. The tablet should be swallowed whole with water. You should not take more than one dose in any 24-hour period.

  • Standard starting dose is 50mg, taken 30 to 60 minutes before activity
  • Maximum dose is 100mg in any 24-hour period
  • A high-fat meal can delay onset of action — a light meal is preferable
  • Do not crush, split, or chew tablets unless your pharmacist advises otherwise
  • Avoid grapefruit juice, which can increase plasma concentrations unpredictably
Dose Typical Patient Onset Time Duration Notes
25mg Older men, renal or hepatic impairment 30–45 minutes 4–5 hours Starter dose where sensitivity is a concern
50mg Most adult men, standard first prescription 30–60 minutes 4–6 hours Most commonly dispensed strength in the UK
100mg Men where 50mg is insufficient 30–60 minutes 4–6 hours Maximum permitted dose; not suitable for everyone

Side Effects and Who Should Avoid Sildenafil Citrate

Like any medicine, what's sildenafil citrate comes with a side-effect profile that patients deserve to know about honestly and clearly. The good news is that the majority of men tolerate it very well, and serious adverse events are rare when the drug is used correctly and prescribed by a qualified professional.

The most commonly reported side effects are mild and transient. These include facial flushing (a feeling of warmth or redness in the face), headache, nasal congestion, indigestion, and temporary visual disturbances such as a slight blue tint or increased light sensitivity. These effects are dose-dependent, meaning higher doses are more likely to produce noticeable side effects. They typically resolve within a few hours as the drug is metabolised.

More serious, though rare, side effects include sudden hearing loss, priapism (a prolonged and painful erection lasting more than four hours), and severe drops in blood pressure — particularly when combined with nitrates. Nitrate-based medicines, including glyceryl trinitrate patches, sprays, or tablets used for angina, are an absolute contraindication. The combination can cause a catastrophic fall in blood pressure that requires emergency treatment. Men taking alpha-blockers for prostate problems should also use sildenafil with caution. Always disclose your full medication list to your prescriber before starting treatment.

  • Common: flushing, headache, nasal congestion, indigestion, mild visual changes
  • Uncommon: dizziness, palpitations, rash, muscle pain
  • Rare but serious: priapism, sudden vision loss, sudden hearing loss
  • Absolute contraindication: use with nitrates or nitric oxide donors
  • Caution required with alpha-blockers, antifungals, HIV protease inhibitors, and ritonavir

Sildenafil Citrate vs Other ED Treatments

Sildenafil citrate is not the only ED treatment available, and understanding what's sildenafil citrate means putting it in context alongside its alternatives. Several other PDE5 inhibitors are licensed and widely used in the UK, each with a slightly different profile in terms of onset time, duration, and flexibility. Knowing your options helps you have a more informed conversation with your prescriber or pharmacist.

Tadalafil, sold under the brand name Cialis, is the most notable alternative. Unlike sildenafil, tadalafil has a significantly longer duration of action — up to 36 hours — which gives couples a wider and more spontaneous window. Tadalafil (Teva) and Cialis (Tadalafil) are both popular choices for men who find the time-sensitive nature of sildenafil restrictive. Vardenafil, marketed as Vardenafil Generic Levitra, has a slightly faster onset and is considered by some prescribers to have a more favourable side-effect profile in men with diabetes. Avanafil, available as Spedra (Avanafil) Tablets, is the fastest-acting of the group, with some men noticing effects within 15 minutes.

The choice between these treatments is genuinely personal and clinical. Sildenafil citrate remains first-line in many NHS guidelines primarily due to its extensive evidence base, cost-effectiveness, and the fact that it has been used safely for more than 25 years. It is also worth noting that sildenafil is licensed for pulmonary arterial hypertension under the brand Revatio, at lower doses — though this is a separate clinical indication from ED.

  • Tadalafil lasts up to 36 hours — ideal for spontaneous intimacy
  • Vardenafil may suit men with diabetes or those sensitive to sildenafil's side effects
  • Avanafil has the fastest onset time of all current PDE5 inhibitors
  • Sildenafil citrate remains the most widely prescribed and most affordable option
  • All PDE5 inhibitors share the same nitrate contraindication — this is not unique to sildenafil

How and Where to Buy Sildenafil Citrate Safely in the UK

Buying sildenafil citrate safely is just as important as understanding what's sildenafil citrate and how it works. The rise of online pharmacies has transformed access to ED treatment, removing the barrier of an awkward face-to-face consultation for many men. However, it has also created a market flooded with unregulated, counterfeit, and potentially dangerous products sold by illegitimate websites.

In the UK, sildenafil citrate is classified as a prescription-only medicine (POM) above 50mg. Viagra Connect 50mg is available directly from pharmacies without a prescription for adult men, following a pharmacist consultation. However, higher doses and all other branded or generic sildenafil products require a valid UK prescription. Any website selling sildenafil at 100mg without requiring a prescription is operating outside UK law. Genuine online pharmacies in the UK are registered with the General Pharmaceutical Council (GPhC) and display the EU common logo for online pharmacies.

At Cured Pharmacy, all sildenafil citrate orders go through a safe clinical pathway, reviewed by UK-based prescribing pharmacists. This means patients receive a genuine prescription review, appropriate medical advice, and discreet delivery of their medication. Options available include Arotix Sildenafil 50mg (4 Pack) for those looking for a starter supply, and Viagra Connect 50mg for those who prefer a recognised brand. The process takes minutes and avoids unnecessary delays in getting the help you need.

  • Always buy from a GPhC-registered UK pharmacy to guarantee authenticity
  • Prescription-only versions require a valid UK prescription — this protects your safety
  • Counterfeit sildenafil tablets may contain wrong doses or dangerous contaminants
  • Online prescribing services allow discreet, legitimate access without a GP appointment
  • Check that any online pharmacy displays the EU common logo and a GPhC registration number

Key Takeaways

  • Sildenafil citrate is a PDE5 inhibitor that treats erectile dysfunction by allowing blood vessels in the penis to relax and fill with blood during sexual arousal
  • It requires sexual stimulation to work and typically takes effect within 30 to 60 minutes of taking a tablet
  • The standard starting dose is 50mg, with options to adjust to 25mg or 100mg based on individual response and tolerability
  • It must never be taken with nitrate-based heart medicines due to the risk of a severe and potentially life-threatening drop in blood pressure
  • Generic sildenafil citrate is widely available from registered UK pharmacies and offers the same clinical efficacy as branded Viagra at a fraction of the cost

When to Seek Professional Advice

Erectile dysfunction is not simply a quality-of-life issue — it can sometimes be an early warning sign of underlying cardiovascular disease, diabetes, hormonal imbalance, or psychological conditions such as depression and anxiety. If you have recently developed ED and have not been investigated medically, it is worth speaking to your GP before starting any treatment. This is especially true if you are under the age of 40, as ED in younger men often has an identifiable and treatable cause.

You should seek immediate medical attention if you experience an erection lasting more than four hours after taking sildenafil citrate — this is a medical emergency known as priapism, and delaying treatment can cause permanent damage. Similarly, sudden vision or hearing loss following a dose must be reported to a doctor immediately. If sildenafil citrate stops working after previously being effective, this can sometimes indicate a change in your underlying health and warrants a medication review rather than simply increasing the dose.

If you are unsure whether sildenafil citrate is right for you, a consultation with a GPhC-registered prescribing pharmacist through Cured Pharmacy can help you make an informed decision safely and discreetly from your own home.

Scientific References

  1. electronic Medicines Compendium (eMC) — Sildenafil 50mg Film-Coated Tablets: Summary of Product Characteristics [Accessed 12 August 2026]
  2. British National Formulary (BNF) via NICE — Sildenafil: Drug Monograph [Accessed 12 August 2026]
  3. NICE Clinical Guideline CG97 — Lower Urinary Tract Symptoms in Men: Management (including ED guidance) [Accessed 12 August 2026]
  4. Sildenafil monograph, British National Formulary (BNF), NICE, 2024 [Accessed 12 August 2026]
  5. Viagra 25 mg, 50 mg and 100 mg film-coated tablets – Summary of Product Characteristics, Electronic Medicines Compendium (EMC), Viatris UK Healthcare, 2023 [Accessed 12 August 2026]
  6. Sildenafil for erectile dysfunction, Technology Appraisal TA36, National Institute for Health and Care Excellence (NICE), 2002 [Accessed 12 August 2026]
  7. Sildenafil now available without prescription, Medicines and Healthcare products Regulatory Agency (MHRA), 2018 [Accessed 12 August 2026]
  8. Fertility problems: assessment and treatment – NICE Clinical Guideline CG163, National Institute for Health and Care Excellence, 2013 (updated 2017) [Accessed 12 August 2026]
  9. Pulmonary hypertension – diagnosis and management, NICE Guideline NG45, National Institute for Health and Care Excellence, 2016 [Accessed 12 August 2026]

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Frequently Asked Questions

How long does sildenafil citrate take to work?

Sildenafil citrate typically takes between 30 and 60 minutes to work after swallowing a tablet. It is best taken on an empty stomach because a fatty meal can slow absorption significantly. The effects can last for up to four to six hours, giving a reasonable window for sexual activity.

Is sildenafil citrate safe to take every day?

Sildenafil citrate is generally safe for most healthy men when taken as directed, but it is not usually prescribed as a daily medication at standard doses. A doctor may recommend a lower daily dose in specific clinical circumstances. You should always follow your prescriber's guidance and disclose all other medications you take.

Can you take sildenafil citrate with alcohol?

Taking sildenafil citrate with alcohol is not recommended in large quantities. Both substances can lower blood pressure, and combining them may increase the risk of dizziness, flushing, or fainting. A small amount of alcohol is unlikely to cause serious problems, but heavy drinking should be avoided when using sildenafil citrate.

What is the correct dose of sildenafil citrate for erectile dysfunction?

The standard starting dose of sildenafil citrate for erectile dysfunction is 50mg, taken approximately one hour before sexual activity. Depending on how well it works and how well it is tolerated, the dose can be adjusted to 25mg or increased to 100mg. A prescriber will recommend the most appropriate dose for your individual situation.

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