Sildenafil and Viagra are the same medicine. Viagra is the brand name that Pfizer gave to sildenafil citrate when it launched in 1998; generic sildenafil is the same active ingredient made by other manufacturers after Pfizer's UK patent expired in 2013. Both work identically, carry the same side-effect profile, and come in the same three strengths. The only real differences are the name on the box and the price you pay.
If that answers your question, you can stop here. If you want the full picture, including how the two compare on cost, how Viagra Connect fits in, who can and cannot take sildenafil, and what alternatives exist, keep reading.
In this article
- Are sildenafil and Viagra the same thing?
- How does sildenafil work?
- Sildenafil vs Viagra: the comparison
- What about Viagra Connect?
- Which dose should you take?
- What are the side effects?
- Who should not take sildenafil?
- Can you get sildenafil on the NHS?
- What are the alternatives?
- Frequently asked questions
Are sildenafil and Viagra the same thing?
Yes. Sildenafil citrate is the active pharmaceutical ingredient in both products. When Pfizer developed the compound in the 1990s, it was originally being tested for angina and pulmonary hypertension. The erectile dysfunction benefit was an unexpected finding during clinical trials. Pfizer patented the compound and marketed it under the brand name Viagra from 1998.
When that patent expired in the UK in June 2013, other licensed manufacturers were allowed to produce generic sildenafil. Before a generic can reach the market, it must demonstrate bioequivalence to the branded original, meaning the active ingredient reaches the same levels in the body at the same rate. The Medicines and Healthcare products Regulatory Agency (MHRA) oversees this process in the UK.
In practical terms, a 50mg sildenafil tablet from any licensed manufacturer does the same job as a 50mg Viagra tablet from Pfizer.
How does sildenafil work?
Sildenafil belongs to a class of medicines called PDE5 inhibitors. During sexual arousal, the body releases nitric oxide, which triggers the production of a chemical called cGMP. cGMP relaxes the smooth muscle in the blood vessels of the penis, allowing blood to flow in and produce an erection.
An enzyme called PDE5 breaks down cGMP. Sildenafil blocks PDE5, so cGMP levels stay higher for longer, and the erection is easier to achieve and maintain. It does not cause an erection on its own. Sexual stimulation is still needed.
It typically takes 30 to 60 minutes to start working. The effects last for 4 to 6 hours, though this varies between individuals. A heavy meal or excessive alcohol can delay the onset or reduce effectiveness.
Sildenafil vs Viagra: the full comparison
| Feature | Generic Sildenafil | Viagra (Pfizer) |
|---|---|---|
| Active ingredient | Sildenafil citrate | Sildenafil citrate |
| Available strengths | 25mg, 50mg, 100mg | 25mg, 50mg, 100mg |
| Onset | 30 to 60 minutes | 30 to 60 minutes |
| Duration | 4 to 6 hours | 4 to 6 hours |
| Prescription required? | Yes (25mg, 50mg, 100mg) | Yes (25mg, 50mg, 100mg) |
| Typical UK price per tablet | From around £0.89 | From around £5.00 |
| Appearance | White or blue tablet (varies by manufacturer) | Blue diamond-shaped tablet marked "Pfizer" and "VGR" |
| Side effects | Identical | Identical |
| Effectiveness | Identical (bioequivalent) | Identical (bioequivalent) |
The table makes the point clearly: the clinical profile is identical across every measure. The only practical difference is cost.
What about Viagra Connect?
Viagra Connect is a separate product. In November 2017, the MHRA reclassified sildenafil 50mg from prescription-only (POM) to pharmacy medicine (P), meaning it could be sold without a prescription after a consultation with a pharmacist. Pfizer launched this as Viagra Connect in March 2018, making the UK the first country to allow over-the-counter sales of an erectile dysfunction treatment.
Key differences from prescription sildenafil:
- Dose: Viagra Connect is available in 50mg only. Prescription sildenafil comes in 25mg, 50mg, and 100mg.
- Access: No prescription needed, but you must have a consultation with a pharmacist (in person or online) who will assess whether the medicine is appropriate for you.
- Age: Available to men aged 18 and over.
- Price: Typically more expensive per tablet than generic sildenafil bought with a prescription, but more convenient if you prefer not to see a GP.
- Pack sizes: Usually sold in packs of 4 or 8 tablets.
The active ingredient is still sildenafil citrate, so the medicine itself works identically. The difference is the route to getting it.
Which dose should you take?
Sildenafil is available in three strengths. Your prescriber will recommend a starting dose based on your health, other medications, and the severity of your symptoms.
- 25mg: The lowest dose. Sometimes prescribed for men who experience side effects at 50mg, or those taking medicines that increase sildenafil levels in the body (such as certain HIV treatments or antifungals).
- 50mg: The standard starting dose for most men. This is also the dose available as Viagra Connect without a prescription.
- 100mg: The highest dose. Used when 50mg has been tried on several occasions without adequate results. Not available over the counter.
Take it approximately one hour before you expect to need it. Do not take more than one tablet in 24 hours. It can be taken with or without food, but a heavy, high-fat meal may delay the onset.
What are the side effects?
Because the active ingredient is the same, sildenafil and Viagra share an identical side-effect profile. Most side effects are mild and short-lived.
Common side effects (reported by more than 1 in 10 users in clinical trials):
- Headache
- Flushing (warmth or redness in the face)
Less common side effects:
- Dizziness
- Blocked or stuffy nose
- Stomach discomfort, nausea, or indigestion
- Temporary changes in vision (such as a blue tinge or blurred vision)
Rare but serious side effects (seek immediate medical attention):
- Priapism: a painful erection lasting longer than 4 hours. This is a medical emergency.
- Sudden loss of vision in one or both eyes
- Sudden hearing loss or ringing in the ears
- Chest pain or an irregular heartbeat
- Seizures or fainting
- A severe allergic reaction (difficulty breathing, swelling of face/lips/throat)
If you experience any of the serious side effects above, stop taking the medicine and call 999 or go to A&E immediately.
Who should not take sildenafil?
Sildenafil is not suitable for everyone. You should not take it if you:
- Take nitrates for angina (such as glyceryl trinitrate or isosorbide mononitrate), as the combination can cause a dangerous drop in blood pressure
- Take recreational drugs known as poppers (amyl nitrite), for the same reason
- Have recently had a heart attack or stroke
- Have severe liver or kidney disease
- Have very low blood pressure (hypotension) or uncontrolled high blood pressure
- Have a condition affecting the shape of the penis, such as Peyronie's disease, where it causes painful erections
- Have been advised not to have sexual activity for medical reasons
- Have a rare inherited eye condition called retinitis pigmentosa
- Have had a previous episode of non-arteritic anterior ischaemic optic neuropathy (NAION)
Always tell your prescriber or pharmacist about all the medicines you take, including herbal remedies such as St John's Wort. Grapefruit juice can increase the level of sildenafil in your blood and should be avoided.
Can you get sildenafil on the NHS?
Yes. Sildenafil has been available on NHS prescription for erectile dysfunction since 2014, when the Department of Health removed previous restrictions that had limited prescribing to certain patient groups (such as those with diabetes, spinal cord injury, or prostate surgery).
Your GP can prescribe generic sildenafil. With a standard NHS prescription, you pay the current prescription charge (currently £9.90 per item in England; free in Scotland, Wales, and Northern Ireland). Because a prescription can cover multiple tablets, this often works out cheaper per tablet than buying Viagra Connect over the counter.
If you are exempt from prescription charges (for example, if you have a medical exemption certificate, are over 60, or receive certain benefits), the cost is zero.
Some men prefer to buy privately from an online pharmacy to avoid the GP appointment. This is a legitimate option provided you use a pharmacy registered with the General Pharmaceutical Council (GPhC). Check the GPhC register at pharmacyregulation.org before ordering.
What are the alternatives to sildenafil?
Sildenafil is one of several PDE5 inhibitors licensed for erectile dysfunction in the UK. If sildenafil does not suit you, or if you are looking for a different duration of action, your prescriber may suggest one of these:
| Medicine | Brand name | Onset | Duration | Key difference |
|---|---|---|---|---|
| Sildenafil | Viagra | 30 to 60 min | 4 to 6 hours | The original; most widely used |
| Tadalafil | Cialis | 30 to 60 min | Up to 36 hours | Much longer duration; also available as a daily low dose |
| Vardenafil | Levitra | 25 to 60 min | 4 to 6 hours | May be better tolerated by men with diabetes |
| Avanafil | Spedra | 15 to 30 min | 4 to 6 hours | Fastest onset; fewer food interactions |
All PDE5 inhibitors work by the same mechanism. The choice between them usually comes down to how long you want the effects to last, how quickly you need it to work, and how your body responds to each one.
Frequently asked questions
Is sildenafil as good as Viagra?
Yes. Generic sildenafil is bioequivalent to Viagra, meaning it contains the same active ingredient at the same concentration and works in the same way. The MHRA requires manufacturers to prove bioequivalence before a generic can be licensed. In clinical terms, there is no difference in effectiveness or safety.
Why is sildenafil so much cheaper than Viagra?
Competition. Once Pfizer's patent expired in 2013, multiple manufacturers were allowed to produce generic sildenafil. When several companies make the same product, prices fall. Pfizer, as the sole maker of branded Viagra, sets its own price without that competitive pressure.
Can I buy sildenafil without a prescription in the UK?
You can buy Viagra Connect (sildenafil 50mg) without a prescription from a pharmacy after a consultation with a pharmacist. This has been available since March 2018. For other strengths (25mg or 100mg), you need a prescription from a doctor or an authorised prescriber.
How long does sildenafil take to work?
It usually takes 30 to 60 minutes, though some men notice the effect sooner. Taking it on an empty stomach or with a light meal gives the fastest results. A heavy, high-fat meal can delay the onset.
How long does sildenafil last?
The effects typically last 4 to 6 hours. This does not mean you will have an erection for 4 to 6 hours. It means that during that window, you should find it easier to achieve and maintain an erection when sexually stimulated.
Can I take sildenafil every day?
Sildenafil is usually taken as needed, not daily. It should not be taken more than once in 24 hours. If you find yourself needing erectile dysfunction treatment more frequently, speak to your prescriber about tadalafil, which is available as a daily low-dose option (2.5mg or 5mg).
Is it safe to buy sildenafil online?
Yes, provided you use a UK-registered online pharmacy. Legitimate online pharmacies are registered with the General Pharmaceutical Council (GPhC) and will require an online consultation before dispensing. Avoid unregulated websites selling "generic Viagra" without a consultation, as these products may be counterfeit, contaminated, or incorrectly dosed.
Can I drink alcohol with sildenafil?
Small amounts of alcohol are unlikely to cause problems, but excessive drinking can make it harder to achieve an erection and may increase the risk of side effects such as dizziness and low blood pressure. The NHS advises limiting alcohol when taking sildenafil.
Medical disclaimer: This article is for general information only and does not constitute medical advice. Sildenafil is a prescription-only medicine (except Viagra Connect 50mg, which is a pharmacy medicine). Always follow the advice of your prescriber or pharmacist and read the patient information leaflet supplied with your medicine. If you have concerns about erectile dysfunction, speak to your GP or a qualified healthcare professional.
