The blue pill is the nickname for Viagra, one of the best-known treatments for erectile dysfunction (ED). It's blue, it's diamond-shaped, and it's been helping men get and keep erections since the late 1990s.
But more than one tablet goes by that name, and there are plenty of fakes too. Here's how Viagra works, how long it lasts, what the side effects are, and how to make sure you're getting the real thing.
Whatever it's called, sildenafil is the active ingredient in every genuine version of Viagra.
What is the blue pill?
"The blue pill" (or "the little blue pill") usually means Viagra. The name comes from the tablet itself: blue, rounded and diamond-shaped, with "VIAGRA" stamped on one side.1
Viagra contains a medicine called sildenafil. It's licensed for adult men with ED, which is when you can't get or keep an erection firm enough for sex.1
It was developed by Pfizer and first licensed in the UK in September 1998. These days, it's marketed in the UK by Viatris.1
Viagra Connect looks very similar and often gets called the blue pill too. More on that below.
How does Viagra work?
Viagra helps more blood reach the penis, but it won't give you an erection without sexual arousal.
When you're aroused, your body releases a chemical called nitric oxide in the penis. This raises the level of a molecule called cGMP. cGMP relaxes the muscle in the penis so blood can flow in, and that's what creates an erection.1
An enzyme called PDE5 breaks cGMP down. Sildenafil blocks PDE5, so cGMP sticks around for longer and more blood can reach the penis.1 That's why Viagra and its relatives are called PDE5 inhibitors.
It won't give you an erection on its own. You still need to be sexually aroused for it to work.1
Does it actually work? In clinical studies, 74% of men taking 50 mg said their erections improved, compared with 25% of men taking a placebo (a dummy pill).1 Results vary depending on what's causing your ED and your general health.
Want the bigger picture on the condition itself? Our guide to erectile dysfunction covers causes, symptoms and treatment options.
How long does Viagra take to work?
The usual advice is to take it about an hour before sex.1
Some men notice it sooner. In one study of men who hadn't eaten, the median time to an erection firm enough for sex was 25 minutes.1
Food slows things down. Taking it with a meal delays absorption by around an hour on average.1 So an empty stomach, or a light meal, tends to work best.
How long does Viagra last?
Think of it as an opportunity, not a timer. Arousal still decides when an erection happens.
Sildenafil can still help you get an erection 4 to 5 hours after you take it. Its half-life (the time it takes for the amount in your blood to halve) is 3 to 5 hours.1
That doesn't mean a 4-hour erection. It means that during this window, you can get an erection when you're aroused. After you ejaculate, your erection goes down as normal.
If an erection lasts longer than 4 hours, get medical help immediately. This is called priapism and, if it is not treated quickly, it can cause permanent damage to the penis.1
How to take Viagra
Swallow the tablet whole with a glass of water, about an hour before sex. Do not take more than one dose in 24 hours.1
Viagra comes in three strengths.1
- 25 mg - a lower starting dose for some men, including those with severe kidney problems, liver problems, or who take certain other medicines such as alpha-blockers
- 50 mg - the usual starting dose for most men
- 100 mg - the maximum dose, used if 50 mg isn't enough and side effects are manageable
Do not take a second tablet the same day, even if the first doesn't seem to have worked.
Your prescriber will choose the right strength based on your health and any other medicines you take. Do not change your dose without speaking to them first.
A couple of other things worth knowing. Grapefruit juice can raise the amount of sildenafil in your blood.1 In studies, sildenafil didn't add to the blood pressure lowering effect of moderate amounts of alcohol.1 But drinking a lot can make erections harder to get in the first place.
Viagra, sildenafil or Viagra Connect?
Three tablets usually get called the blue pill. They all contain the same active ingredient: sildenafil.
Viagra
The original branded version. It's prescription-only and comes in 25 mg, 50 mg and 100 mg tablets.
Sildenafil (generic Viagra)
Sildenafil is the generic version of Viagra. Same active ingredient, same way of working, same strengths. The only real differences are the branding and the price.
The colour and shape depend on the manufacturer. So generic sildenafil isn't always blue.
Viagra Connect
Viagra Connect contains 50 mg of sildenafil. In 2017, the MHRA reclassified it as a pharmacy medicine. That means men aged 18 and over can get it without a prescription, after a discussion with a pharmacist.2
It isn't suitable for men with severe heart problems, liver failure or severe kidney failure, or men who take certain interacting medicines.2 It only comes in one strength: 50 mg.
All three work the same way. The real differences are price, branding, strength options and whether you need a prescription.
Other ED tablets that aren't blue
Sildenafil isn't your only option. Several other ED tablets work in the same way, by blocking PDE5. Where they differ is how quickly they kick in and how long they last.
Not sure which fits your lifestyle? Our guide on choosing the right ED treatment walks you through it.
Tadalafil and Cialis
Tadalafil is the generic version of Cialis, a yellow tablet. Tadalafil has a half-life of around 17.5 hours and can work for up to 36 hours, which is why it's nicknamed "the weekend pill".3
It comes in 2.5 mg and 5 mg for daily use, and 10 mg and 20 mg for taking before sex.3
Cialis Together
Cialis Together is a pharmacy version of tadalafil 10 mg. Like Viagra Connect, you can get it without a prescription after a consultation with a pharmacist.
Vardenafil
Vardenafil is the generic version of Levitra. It's another prescription PDE5 inhibitor that works in the same way as sildenafil.
Spedra
Spedra contains avanafil and comes as a pale yellow, oval tablet. It's taken around 15 to 30 minutes before sex, which suits men who'd rather not plan too far ahead.4
What are the side effects of Viagra?
Most men get on well with it. In clinical studies, the number of men who stopped taking sildenafil because of side effects was low and similar to placebo.1
The most common side effects are listed below.
- Headache - very common (more than 1 in 10 men)
- Flushing or hot flushes - common (up to 1 in 10 men)
- Blocked or stuffy nose - common
- Indigestion or feeling sick - common
- Dizziness - common
- Changes to your vision - common. This can include a coloured tinge to your vision or blurred vision
Less common side effects (up to 1 in 100 men) include a fast or pounding heartbeat, nosebleeds, muscle aches, being sick, a rash and chest pain.1
Rare doesn't mean never. Get urgent help for chest pain, sudden sight or hearing loss, or an erection lasting over 4 hours.
Rare but serious side effects (up to 1 in 1,000 men) include priapism, sudden loss of vision, sudden hearing loss, heart attack and stroke. Most men who had serious heart problems after taking sildenafil already had heart risk factors.1
Who should not take Viagra?
This medicine isn't safe for everyone. You must not take it if any of these apply to you.1
- You take nitrates, such as GTN spray or isosorbide mononitrate for angina
- You use "poppers" (amyl nitrite)
- You take nicorandil or riociguat
- You've recently had a stroke or heart attack
- You have very low blood pressure (below 90/50)
- You have severe liver problems
- You've been told to avoid sex because of a heart condition, such as unstable angina or severe heart failure
- You've lost vision in one eye because of a condition called NAION, or you have an inherited eye condition such as retinitis pigmentosa
Never combine Viagra with nitrates or poppers, and run every other medicine you take past your prescriber.
Speak to a prescriber before taking it if you take alpha-blockers (often used for prostate problems or high blood pressure) or HIV medicines such as ritonavir. The same goes if you have Peyronie's disease (a curved penis), sickle cell anaemia or a bleeding disorder.1
Fake Viagra: what to watch out for
ED tablets are one of the most commonly faked medicines in the UK. Between 2021 and 2025, the MHRA seized around 19.5 million doses of illegally traded ED medicines. That includes 4.4 million doses in 2025 alone.5
These pills can look genuine. But they may contain no active ingredient, the wrong dose, hidden drugs or toxic ingredients. The risks are even higher if you have heart disease or high blood pressure, or you take other medicines.5
The MHRA has seized millions of fake ED pills in recent years, and many look just like the real thing.
Kamagra is a common example. It's often sold as a blue tablet or an oral jelly and claims to contain sildenafil. But it isn't licensed in the UK, and the MHRA regularly seizes it.6
The same goes for "herbal" or "natural" Viagra alternatives. They aren't licensed ED medicines, so there's no guarantee of what's actually in them.
The safest move? Only get ED treatment from a UK-registered pharmacy.
Where can I get Viagra?
Every route involves a health check, whether that's with a prescriber or a pharmacist.
Viagra and generic sildenafil are prescription-only medicines. You can get a prescription from your GP, or through an online consultation with a registered pharmacy like Pharmica, where a prescriber checks the treatment is safe for you.
Viagra Connect doesn't need a prescription. But a pharmacist will still ask you some questions first, to make sure it's right for you.2
Either way, be honest about your health and any other medicines you take. It's the best way to end up with a treatment that works and is safe for you.
When should you seek medical advice?
Stop taking sildenafil and get medical help immediately if:
- Your erection lasts longer than 4 hours
- You suddenly lose some or all of your vision
- You suddenly lose your hearing, or it suddenly gets worse
- You get chest pain during or after sex
Speak to your GP or prescriber if:
- Side effects are bothering you or do not settle
- Your treatment does not work after a few tries
- You're having erection problems for the first time, as ED can have an underlying cause that's worth checking
Frequently asked questions
Does Viagra make you last longer?
Not really. Viagra is licensed to help you get and keep an erection, not to delay ejaculation. Some men feel more relaxed once their erections are more reliable, which can help, but it isn't a treatment for premature ejaculation. If finishing too quickly is the main issue, a pharmacist or GP can talk you through treatments designed for that.
No. Viagra is only licensed for adult men with erectile dysfunction, and it isn't licensed for use by women. If you're a woman and you've noticed changes in your sex drive or arousal, it's worth speaking to your GP. There can be lots of different causes, and they can talk you through the options that are right for you.
Can you drink alcohol with Viagra?
A moderate amount of alcohol is unlikely to cause a problem with Viagra. But drinking a lot can make it harder to get an erection in the first place, which works against the treatment. Alcohol may also make side effects like dizziness and flushing feel worse. If you're unsure, ask your pharmacist.
How long does Viagra stay in your system?
Sildenafil has a half-life of 3 to 5 hours, which means the amount in your blood halves in that time. Most of it will have left your system within about a day. The window where it can help with erections is shorter, at around 4 to 5 hours. Do not take more than one dose in 24 hours.
Can you take Viagra every day?
You can take it on more than one day if you need to, but never more than once in 24 hours. It's designed to be taken when you need it, about an hour before sex. If you'd rather not plan around a tablet, a prescriber may suggest low-dose tadalafil instead, which is licensed for daily use.
Does Viagra make you bigger?
No. Viagra doesn't change the size of your penis. It improves blood flow so you can get and keep a firmer erection when you're aroused. If you've had ED for a while, your erections may feel fuller than they have recently, but it won't make you bigger than your natural erect size.
References
- Viatris. Viagra 50 mg film-coated tablets: Summary of Product Characteristics. Electronic Medicines Compendium; 2025. medicines.org.uk/emc
- 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
- Medicines and Healthcare products Regulatory Agency. 20 million illegal erectile dysfunction pills seized as MHRA warns against risky online buys. GOV.UK; 2026. gov.uk
- Chemist+Druggist. Man arrested with £1m in erectile dysfunction drugs. Chemist+Druggist. 2015. chemistanddruggist.co.uk
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.