Viagra is probably the best-known erectile dysfunction (ED) treatment in the world. But you'll often see it sold alongside Sildenafil. So what's the difference between sildenafil vs Viagra, and does it matter which one you choose?
Here's the short answer: they contain exactly the same active ingredient and work in exactly the same way. This guide explains where they came from, what's the same, what's different, and how they compare with other ED treatments.
Sildenafil and Viagra are the same medicine. The differences come down to the brand name, packaging and how the tablet looks.
Is sildenafil the same as Viagra?
Yes. Viagra is the brand name, and sildenafil is the name of the active ingredient. Generic sildenafil tablets contain the same medicine, in the same strengths, as branded Viagra.1
A brief history
Viagra was the first tablet treatment for ED, launched in the UK in 1998. For years, it was the only sildenafil treatment available here because the original manufacturer held the patent.
That patent expired in the UK in 2013. Other manufacturers could then make their own versions, sold under the name sildenafil.2
How do Viagra and sildenafil work?
Both contain sildenafil citrate, which belongs to a group of medicines called PDE5 inhibitors.1
When you're sexually aroused, your body releases a chemical called cGMP that relaxes the blood vessels in your penis so more blood can flow in. An enzyme called PDE5 normally breaks cGMP down. Sildenafil blocks PDE5, so blood flow is easier to build and maintain.1
That's why neither tablet causes an erection on its own. You still need sexual stimulation for them to work.
How long do they take to work and last?
Take either tablet about an hour before sex. They usually start working within 30 to 60 minutes, and the effect lasts for around 4 hours.1 A heavy, high-fat meal can delay how quickly they kick in.1 Feeling nervous can also make it harder to get an erection, especially the first time you try a new treatment.
A disappointing first try is common, so it's worth giving treatment a few goes before deciding it isn't for you.
Which doses are available?
Viagra and sildenafil both come in 25mg, 50mg and 100mg strengths.1
- 50mg - the usual starting dose for most men
- 100mg - may be suggested if 50mg isn't working well enough
- 25mg - may be suggested if side effects are bothering you at 50mg
Do not take more than one tablet in 24 hours.1
How are Viagra and sildenafil different?
Generic medicines have to meet the same standards of quality, safety and effectiveness as the branded version before they can be sold in the UK. So the differences are mostly practical.
Branding and packaging
Viagra is the branded product. Sildenafil is made by several different manufacturers, so the box and the tablets can look different depending on who makes them.
Tablet appearance
Viagra is famous as the "little blue pill" because of its blue, diamond-shaped tablets. Our guide to the little blue pill has more on its history. Sildenafil tablets vary in colour, shape and size between manufacturers.
Inactive ingredients
The active ingredient is identical, but the inactive ingredients, such as the coating and colourings, can vary between manufacturers. This only really matters if you have an allergy or intolerance to a particular ingredient, such as lactose. Check the leaflet if you're unsure.
If you've reacted to an ingredient in one brand before, check the leaflet of any new sildenafil you're given, as fillers and coatings can differ.
Viagra Connect vs sildenafil 50mg
Viagra Connect contains 50mg of sildenafil, the same as sildenafil 50mg and Viagra 50mg.
The difference is how you get it. In 2017, the MHRA reclassified Viagra Connect so it can be sold by pharmacies without a prescription, after a conversation with a pharmacist.3 It's only available in the 50mg strength, while prescription Viagra and sildenafil also come in 25mg and 100mg.
What are the alternatives to Viagra and sildenafil?
Sildenafil isn't the only option. Other PDE5 inhibitors work in a similar way but differ in how quickly they start and how long they last. Our guide to choosing an ED treatment goes into more detail.
Tadalafil and Cialis
Tadalafil is the generic version of Cialis. It lasts much longer than sildenafil, with effects for up to 36 hours, thanks to a half-life of around 17.5 hours.4
It comes as an on-demand tablet or a low-dose tablet taken every day. Cialis Together contains 10mg tadalafil and is available from pharmacies without a prescription.
Vardenafil and Levitra
Vardenafil, the generic version of Levitra, works in a similar way to sildenafil and lasts for a similar length of time.
Spedra (avanafil)
Spedra contains avanafil. It's taken around 15 to 30 minutes before sex, so it may suit men who want a faster-acting option.5
Do not take two different ED tablets together or on the same day. Combining PDE5 inhibitors increases the risk of side effects.
What are the side effects of sildenafil?
Because they're the same medicine, Viagra and sildenafil share the same side effects. Headache is very common, affecting more than 1 in 10 men. Common side effects include flushing, dizziness, indigestion, feeling sick, a blocked nose and changes to vision, such as a blue tinge.1
Get medical help straightaway if you have chest pain, sudden loss of vision, or an erection that lasts longer than 4 hours.1
You must not take sildenafil if you take nitrates for chest pain, or use poppers.1
Frequently asked questions
How long does sildenafil last?
Sildenafil usually works for around 4 hours after you take it. That doesn’t mean a 4-hour erection, though. It means you’re more likely to get an erection if you’re sexually aroused during that window. If an erection lasts longer than 4 hours, get medical help straightaway.
Does Viagra Connect work?
Yes. Viagra Connect contains 50mg of sildenafil, the same as Viagra 50mg and sildenafil 50mg, so it works in exactly the same way. It’s available from pharmacies after a chat with a pharmacist. If it doesn’t work after a few tries, speak to a pharmacist or GP about other doses or treatments.
Is it OK to take 100mg of sildenafil?
100mg is a licensed dose and may be suggested if 50mg isn’t working well enough. You should only take it if a prescriber says it’s suitable, and you must not take more than one tablet in 24 hours. Higher doses can make side effects such as headaches and flushing more likely.
Is tadalafil better than sildenafil?
Neither is better for everyone. They work in a similar way, but tadalafil lasts much longer, up to 36 hours, which some men prefer for spontaneity. Sildenafil works for around 4 hours. Your choice may come down to how you like to plan, how you respond to each, and any side effects you notice.
Viagra Connect is a 50mg sildenafil tablet that can be bought from pharmacies without a prescription, after a conversation with a pharmacist. It was reclassified as a pharmacy medicine by the MHRA in 2017. It’s for men aged 18 and over with erectile dysfunction.
References
- Viatris. Viagra 50 mg film-coated tablets: Summary of Product Characteristics. Electronic Medicines Compendium; 2025. medicines.org.uk/emc
- BBC News. Room for growth: Viagra patent ends. BBC News. 2013. bbc.co.uk
- Medicines and Healthcare products Regulatory Agency. MHRA reclassifies Viagra Connect tablets to a Pharmacy medicine. GOV.UK; 2017. gov.uk
- Coward RM, Carson CC. Tadalafil in the treatment of erectile dysfunction. Therapeutics and Clinical Risk Management. 2008;4(6):1315-1330. doi:10.2147/tcrm.s3336
- A. Menarini Farmaceutica Internazionale. Spedra 100 mg tablets: Summary of Product Characteristics. Electronic Medicines Compendium; 2024. medicines.org.uk/emc
This article is intended for informational purposes only and does not replace professional medical advice. Always read the patient information leaflet supplied with your medication and speak to a healthcare professional if you have specific concerns.