Sildenafil and Viagra contain the same active ingredient. Viagra is the brand name Pfizer gave sildenafil citrate when it launched as an erectile dysfunction (ED) treatment in 1998; “sildenafil” on its own usually means a generic version made by another manufacturer after the patent expired. Generic sildenafil must meet the same standards for quality, strength and how it is absorbed by the body, so it works in the same way and carries the same side effects and precautions. The main practical differences are price, packaging and appearance. This guide explains how sildenafil works, how the options compare in the UK, who should not take it and how to obtain it safely.
What is erectile dysfunction?
Erectile dysfunction is the regular inability to get or keep an erection firm enough for sex. It is common, especially with age, and occasional difficulty is normal. Causes are often a mix of physical and psychological factors:
- Physical: heart and blood vessel disease, high blood pressure, diabetes, high cholesterol, obesity, hormonal problems and some medicines.
- Lifestyle: smoking, heavy drinking, recreational drug use and lack of exercise.
- Psychological: stress, anxiety, depression and relationship difficulties.
Because ED can be an early sign of conditions such as heart disease or diabetes, the NHS advises speaking to a GP if it keeps happening, even if you plan to buy treatment elsewhere.
How sildenafil works
Sildenafil belongs to a group of medicines called phosphodiesterase type 5 (PDE5) inhibitors. During sexual arousal, the body releases nitric oxide in the penis, which raises levels of a chemical called cGMP. cGMP relaxes smooth muscle and lets blood flow into the erectile tissue. The enzyme PDE5 breaks cGMP down; sildenafil blocks that enzyme, so blood flow is easier to achieve and maintain.
Importantly, sildenafil does not cause an erection by itself and does not increase sexual desire. Sexual stimulation is still needed.
Sildenafil vs Viagra: side-by-side comparison
| Generic sildenafil | Viagra (brand) | Viagra Connect | |
|---|---|---|---|
| Active ingredient | Sildenafil citrate | Sildenafil citrate | Sildenafil citrate |
| Maker | Various licensed manufacturers | Pfizer/Viatris | Viatris |
| Strengths | 25 mg, 50 mg, 100 mg | 25 mg, 50 mg, 100 mg | 50 mg only |
| UK status | Prescription only | Prescription only | Pharmacy medicine after a pharmacist consultation |
| Appearance | Varies by manufacturer | Blue diamond-shaped tablet | Blue tablet |
| Relative cost | Usually the cheapest | Usually more expensive | Usually more expensive than generics |
Pfizer’s UK patent on sildenafil for ED expired in 2013, after which many generic versions were licensed. Generics are approved by the Medicines and Healthcare products Regulatory Agency (MHRA) only after showing they are bioequivalent to the original. Differences in colour, shape or inactive ingredients (fillers and coatings) do not change how the medicine works, although a very small number of people may react to a particular inactive ingredient.
How to take sildenafil
- Timing: usually taken about an hour before sex. It can work from around 30 minutes and remains effective for roughly four to five hours for many people.
- Food: it can be taken with or without food, but a heavy or high-fat meal may delay its effect.
- Dose: 50 mg is a common starting dose. A prescriber may adjust this to 25 mg or 100 mg depending on response, age and other health factors.
- Frequency: no more than one dose in 24 hours.
- Alcohol: large amounts of alcohol can make ED worse and increase the risk of dizziness.
It may take a few attempts to find out how well it works for you. If it does not help after several tries at the prescribed dose, speak to a prescriber rather than increasing the dose yourself.
Side effects
Brand and generic sildenafil share the same side effect profile. Common ones are usually mild and short-lived:
- Headache
- Facial flushing
- Indigestion
- Blocked or runny nose
- Dizziness
- Temporary changes in vision, such as a blue tinge or sensitivity to light
Get urgent medical help if you have chest pain during or after sex, an erection lasting more than four hours (priapism), sudden loss of vision or hearing, or signs of a serious allergic reaction.
Who should not take sildenafil
Sildenafil is not safe for everyone. It must not be taken with nitrates, such as glyceryl trinitrate (GTN) sprays or tablets for angina, or with recreational “poppers”, because the combination can cause a dangerous fall in blood pressure. It is also generally unsuitable, or needs specialist advice, if you:
- Have been advised to avoid sexual activity because of a heart condition
- Have recently had a heart attack or stroke
- Have very low blood pressure or uncontrolled high blood pressure
- Have severe liver or kidney problems
- Have certain inherited eye conditions, or have lost sight in one eye from a condition called NAION
- Take riociguat, alpha blockers, some HIV medicines or certain antifungal and antibiotic medicines
This list is not complete. Always tell the prescriber or pharmacist about every medicine and supplement you take.
How to get sildenafil safely in the UK
There are three main routes:
- Your GP: can assess the cause of ED, check for underlying conditions and prescribe generic sildenafil on the NHS, subject to standard prescription charges where they apply.
- A high street pharmacy: a pharmacist can supply Viagra Connect after a short consultation if it is suitable for you.
- A regulated online pharmacy: you complete a medical questionnaire, a UK prescriber reviews it, and if appropriate the medicine is dispensed and posted in discreet packaging. Services such as Post My Meds offer generic sildenafil through this kind of consultation-based route.
Whichever you choose, avoid websites that sell prescription-only ED medicine without any health questions. The MHRA regularly warns that fake and unlicensed ED tablets bought online may contain the wrong dose, no active ingredient or harmful substances. Before ordering, check that the pharmacy appears on the General Pharmaceutical Council (GPhC) register and that prescribers are registered with a UK regulator such as the GMC or GPhC.
Alternatives to sildenafil
| Medicine | Typical duration of effect | Notes |
|---|---|---|
| Sildenafil | Around 4 to 5 hours | Most widely used, low-cost generics |
| Tadalafil | Up to about 36 hours | Also available as a lower daily dose |
| Vardenafil | Around 4 to 5 hours | Similar profile to sildenafil |
| Avanafil | Around 5 to 6 hours | Can work relatively quickly |
If tablets are unsuitable or ineffective, a doctor may discuss other options such as vacuum devices, injections, hormone treatment where testosterone is low, or psychosexual therapy. Lifestyle changes (stopping smoking, drinking less, regular exercise and losing excess weight) can improve erections and overall health. Some people also explore holistic approaches such as Ayurveda, but herbal “natural Viagra” products are not a substitute for medical assessment and some have been found to contain undeclared prescription drugs.
If sildenafil does not seem to work
Many people who feel sildenafil has “failed” have not given it a fair trial. Before concluding it is not for you, consider these common reasons, and talk them through with your prescriber:
- Too few attempts: prescribers often suggest trying it on several separate occasions before judging the result.
- Timing: taking it too close to sex, or straight after a large meal, can delay or weaken the effect.
- No stimulation: the tablet only works alongside sexual arousal.
- Dose: the starting dose may be too low for you, and a prescriber can review it.
- Underlying causes: untreated diabetes, low testosterone, anxiety or relationship stress can all limit how well it works, which is another reason a proper assessment is worthwhile.
Choosing between generic sildenafil and Viagra
- Cost: generic sildenafil is usually much cheaper for the same dose.
- Effectiveness: expected to be the same, because the active ingredient and dose are identical.
- Convenience: Viagra Connect can be bought from a pharmacy without a prescription, but only in 50 mg.
- Personal preference: some people prefer the familiar brand, and that is a valid choice.
Frequently asked questions
Is sildenafil the same as Viagra?
Yes, in terms of the active ingredient. Viagra is the brand name for sildenafil citrate, and licensed generics contain the same medicine at the same strengths.
Why is generic sildenafil cheaper?
Generic manufacturers do not carry the original research and marketing costs, and competition between several makers keeps prices lower.
Do I need a prescription for sildenafil in the UK?
Generic sildenafil is prescription only, which can come from a GP or a regulated online service. Viagra Connect 50 mg can be supplied by a pharmacist after a consultation.
How long does sildenafil last?
It usually starts working within 30 to 60 minutes and remains effective for around four to five hours, though this varies from person to person.
Can I take sildenafil with heart medicine?
Never take it with nitrates such as GTN. Some other heart and blood pressure medicines also interact, so check with a doctor or pharmacist before use.
This article is general information only and is not medical advice. Speak to a doctor or pharmacist before starting any treatment.
