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Viagra (Sildenafil)
Viagra (sildenafil) is a prescription tablet for erectile dysfunction, taken about an hour before sex. Available as branded Viagra or generic sildenafil in 25mg, 50mg and 100mg.
Free online assessment with a UK prescriber
Viagra is a prescription tablet for erectile dysfunction (ED). It contains sildenafil, which improves blood flow to the penis so you can get and keep an erection when you're sexually aroused. It's usually taken about an hour before sex and works for around 4 to 5 hours. At MedsRus, a UK prescriber reviews a confidential online consultation before supplying branded Viagra or generic sildenafil, and orders are sent in plain packaging.
Viagra at a glance
| Details | |
|---|---|
| Active ingredient | Sildenafil (a PDE5 inhibitor) |
| Used for | Erectile dysfunction in adult men |
| Strengths | 25mg, 50mg and 100mg tablets |
| When to take it | About 1 hour before sex (it can start working in 30 minutes) |
| How long it works | Usually around 4–5 hours |
| How often | No more than one tablet in 24 hours |
| Available as | Branded Viagra or generic sildenafil (same active ingredient) |
| Supply | Prescription-only, after an online consultation |
How does Viagra work?
An erection happens when blood flows into the penis and stays there. In ED, that blood flow isn't strong enough or doesn't last. Sildenafil blocks an enzyme called PDE5, which relaxes the blood vessels in the penis so more blood can flow in when you're aroused.
It doesn't cause an erection on its own and it doesn't increase your sex drive. You still need to feel aroused, and the erection should go away normally after sex.
How long does Viagra last?
Most men find sildenafil works for around 4 to 5 hours. That isn't 4 hours of erection: it's a window in which you can get an erection more easily if you're aroused. The effect fades gradually as your body clears the medicine, so how long it lasts varies from person to person.
A heavy or fatty meal can slow it down. Taking it on a lighter stomach usually helps it work sooner.
If you'd like a longer window, tadalafil (Cialis) can work for up to 36 hours. See our guide Cialis vs Viagra.
Viagra doses: 25mg, 50mg or 100mg?
- 50mg is the usual starting dose for most men.
- 100mg may be suggested if 50mg works but not well enough, and you had no troublesome side effects.
- 25mg is often used if you're over 65, have liver or kidney problems, take certain other medicines, or found 50mg gave you side effects.
Take one tablet with a glass of water about an hour before sex. Don't take more than one tablet in 24 hours, and don't take a higher strength than you've been prescribed: it doesn't make the erection stronger, but it does make side effects more likely.
If it doesn't work the first time, that's common. Try it on several different occasions, as nerves and alcohol can both get in the way, before deciding it isn't for you.
Viagra, generic sildenafil and Viagra Connect: what's the difference?
- Branded Viagra is made by Viatris (originally Pfizer).
- Generic sildenafil contains the same active ingredient at the same strengths and has to meet the same standards. It works the same way and usually costs less.
- Viagra Connect is 50mg sildenafil sold as a pharmacy medicine for men over 18, after a pharmacist checks it's suitable, without a prescription. See Viagra Connect. If you need 25mg or 100mg, or have other health conditions, the prescription route on this page is the right one.
Sildenafil, tadalafil, vardenafil or avanafil?
All four are PDE5 inhibitors and work in the same way. The main differences are how quickly they start working and how long they last.
| Sildenafil (Viagra) | Tadalafil (Cialis) | Vardenafil | Avanafil (Spedra) | |
|---|---|---|---|---|
| Starts working | 30 to 60 minutes | About 30 minutes | 25 to 60 minutes | 15 to 30 minutes |
| Lasts up to | About 4 to 5 hours | 36 hours | About 4 to 5 hours | About 6 hours |
| Affected by food | A heavy meal can slow it down | No | A heavy, fatty meal can slow it down | A heavy meal can slow it down |
If sildenafil doesn't suit you, the prescriber can suggest one of the others.
Side effects of Viagra
Most side effects are mild and wear off as the medicine does.
Common: headache, flushing (warm, red face), indigestion, a blocked or runny nose, dizziness, and changes in vision such as a blue tinge or blurring.
Get medical help straight away if you have:
- an erection that lasts longer than 4 hours (priapism);
- sudden loss or decrease of vision or hearing;
- chest pain during or after sex;
- signs of a serious allergic reaction, such as a swollen face, lips or throat, or difficulty breathing.
Who shouldn't take Viagra?
Don't take sildenafil if you:
- take nitrates for chest pain (including GTN spray), or use "poppers" (amyl nitrite);
- take riociguat for lung blood pressure;
- have had a stroke or heart attack in the last 6 months, have unstable angina, or have very low blood pressure;
- have severe heart or liver problems, or have been told to avoid sex for health reasons;
- have a rare inherited eye condition such as retinitis pigmentosa;
- have lost vision in one eye from NAION (a problem with blood flow to the optic nerve).
Don't take it with ritonavir. Tell the prescriber about all the medicines you take, especially alpha-blockers for blood pressure or prostate problems and some HIV and antifungal medicines, as the dose may need to be lower. Tell them too if you use any other treatment for erection problems.
Viagra and alcohol
A drink or two is unlikely to cause a problem, but alcohol itself makes erections harder to get, and drinking more makes dizziness and headaches more likely.
How MedsRus prescribes Viagra
- Complete a short online consultation about your health and any medicines you take.
- A UK prescriber reviews it. If sildenafil is suitable, they'll approve a strength and pack size, or suggest an alternative.
- Your order is dispensed by our UK pharmacy and sent in plain, discreet packaging.
ED can sometimes be an early sign of conditions such as heart disease, diabetes or high blood pressure. If you haven't had a check-up recently, it's worth seeing your GP as well.
Viagra FAQs
How long before sex should I take Viagra?
About an hour before. It can start working in around 30 minutes, but a heavy meal can delay it.
How long does Viagra last?
Usually around 4 to 5 hours, though this varies between people. It's a window of easier erections when you're aroused, not a continuous erection.
Is generic sildenafil as good as Viagra?
Yes. Generic sildenafil contains the same active ingredient at the same strengths as branded Viagra and works the same way. It's usually cheaper.
Can I take Viagra every day?
You can take it on consecutive days if you need to, but never more than one tablet in 24 hours. If you'd like a daily treatment, ask about low-dose tadalafil.
What's the strongest Viagra?
100mg is the highest strength. A higher strength isn't automatically better: it raises the chance of side effects, so the prescriber will suggest the lowest dose that works for you.
Does Viagra make you last longer?
Not directly. Sildenafil helps with getting and keeping an erection; it isn't a treatment for premature ejaculation. Read more in Does Viagra make you last longer?
Can I drink alcohol with Viagra?
A drink or two is unlikely to cause a problem, but alcohol makes erections harder to get, and drinking more makes dizziness and headaches more likely.
What if Viagra doesn't work?
It often takes a few tries, as nerves, alcohol or a heavy meal can get in the way. If it still doesn't work after 6 to 8 attempts, the prescriber can adjust the dose or suggest a different medicine.
Further reading
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