What Is The Blue Pill And How Does It Work?

What is the little blue pill?

If you've heard someone mention "the blue pill" and wondered whether it could help with erection problems, you're not alone: erectile dysfunction affects around half of men aged 40 to 70. 

In the UK, the phrase usually means Viagra, a blue, diamond-shaped tablet containing sildenafil, a medicine licensed for erectile dysfunction (ED) in adult men. It increases blood flow to the penis, but only with sexual arousal; on its own, it doesn't produce an erection. 

It's an effective treatment for many men, but not everyone responds. In fixed-dose trials, 74% of men taking 50 mg reported better erections, compared with 25% on placebo, and response was lower in some groups (including 59% of men with diabetes and 43% after radical prostatectomy) [1, 2].

Viagra is the branded medication, first authorised in 1998. The same active ingredient is also available as generic sildenafil tablets. Oral liquid formulations of Sildenafil are used for certain indications, but their availability and approval for erectile dysfunction may somewhat differ. Both of them are mostly available on prescription in the UK, though you can buy it from a pharmacy after speaking with a pharmacist [1, 3].

How sildenafil helps an erection start

Sildenafil acts on one step in how an erection works. During sexual stimulation, nitric oxide is released in the erectile tissue of the penis. It raises levels of a messenger molecule called cGMP, which relaxes smooth muscle and lets blood flow in. An enzyme called phosphodiesterase type 5 (PDE5) breaks cGMP down again. Sildenafil blocks PDE5, so once arousal starts the process, cGMP builds up and an erection is easier to get and keep. This way, Sildenafil helps the blood vessels in the penis relax, making it easier for blood to flow in. But sexual stimulation is still needed to start the process that leads to an erection  [1].

The usual starting dose is 50 mg about an hour before sex, adjusted to 25 mg or 100 mg depending on effect and tolerability. In men who took it on an empty stomach, the median time to an erection firm enough for sex was 25 minutes. Taken with a meal, sildenafil reaches its peak level about an hour later on average, and heavy drinking can make an erection harder to get, so it helps to know how to take Viagra before relying on it [1, 3, 4].

It doesn't always work first time. In the Viagra Connect trials, 40.8% of men on 50 mg reported improved erections after the first dose, against 14.6% on placebo, while some only improved after up to eight doses. So if the first attempt doesn't go to plan, it isn't a verdict on you or on the medicine. If several attempts on different days still haven't helped, the advice is to see a doctor [4].

What it is for and what it is not

Sildenafil tablets for erection problems are licensed for adult men who have difficulty getting or keeping an erection firm enough for satisfactory sex. They aren't for women or anyone under 18. Sildenafil is also used for pulmonary arterial hypertension, but as a separate product that shouldn't be combined with erectile dysfunction treatment [1, 3].

It isn't an aphrodisiac. In the Viagra Connect trials, 50 mg had no clinically significant effect on sexual desire, and the pharmacy product isn't intended for men without erectile dysfunction. A single 100 mg dose had no effect on sperm movement or shape in healthy volunteers [1, 4].

It can, though, take some of the pressure off. In one trial of the 50 mg dose, men reported more confidence and less anxiety about attempting sex than men on placebo, and in another, female partners of men taking it reported greater satisfaction with sex [4].

Erection problems can be a sign of conditions such as diabetes, high blood pressure or heart disease, so anyone buying sildenafil without a prescription is advised to have a check-up with their doctor within six months [3, 4].

How long the effect lasts

Sildenafil doesn't cause an erection that lasts for hours. It opens a window in which arousal can lead to one. In one study, it could still produce an erection in response to stimulation four to five hours after the dose, and in the Viagra Connect trials it worked from under an hour to up to four hours after it was taken. Its half-life is three to five hours [1, 4].

Don't take more than one dose a day. An erection lasting longer than four hours (priapism) needs immediate medical help, because without prompt treatment it can damage penile tissue and cause permanent loss of erections [1].

Blue, yellow and orange tablets: how they differ

   

Tablet colour tells you which product you're holding, not how well it works. Viagra is a blue tablet because its coating contains a blue colourant, while generic sildenafil can be white [1, 5]. Cialis (tadalafil) is yellow and almond-shaped, vardenafil can come as yellow-orange round tablets, and Spedra (avanafil) is pale yellow and oval [6, 7, 8].

Sildenafil compared with tadalafil, vardenafil and avanafil

All four block PDE5 and work in the same way, and none works without sexual stimulation. The practical differences are in timing, how long they last and whether food gets in the way [1, 6, 7, 8].

Medicine	When to take it	How long it can work	Half-life	Effect of food
Sildenafil (Viagra)	About 1 hour before sex	Up to 4 to 5 hours after the dose	3 to 5 hours	A meal can delay the effect
Tadalafil (Cialis)	At least 30 minutes before sex	Up to 36 hours after the dose	About 17.5 hours	No effect on absorption
Vardenafil	25 to 60 minutes before sex	Up to 4 to 5 hours (limited data)	About 4 to 5 hours	A high-fat meal can delay the effect
Avanafil (Spedra)	15 to 30 minutes before sex	Not stated in UK product information	About 6 to 17 hours	A meal can delay the effect

Timings and half-lives from each medicine's UK summary of product characteristics [1, 6, 7, 8].

Unlike Viagra, tadalafil isn't slowed down by food, and its effect can last up to 36 hours after a dose, which is why it's sometimes called the weekend pill. It can also be taken as a low daily dose (5 mg) by men who expect to use it at least twice a week [6].

Avanafil was tested specifically for speed. In a trial where men tried to have sex about 15 minutes after a dose, about 25% of attempts succeeded on 100 mg, against about 14% on placebo [8].

A 2021 network meta-analysis of 179 randomised trials involving 50,620 men found every PDE5 inhibitor worked better than placebo. Sildenafil 25 mg and 50 mg ranked highest for improving erectile function, tadalafil 10 mg and 20 mg also performed well, and avanafil was less effective. Sildenafil 100 mg was more often linked to visual disturbances, and vardenafil to a blocked nose [9].

Back pain and muscle aches are common with tadalafil, which rarely affects colour vision (under 0.1% of people in trials), whereas colour distortions are a common side effect of sildenafil [1, 6].

Generics and other tablet forms

Sildenafil sold under its generic name, often called generic Viagra, contains the same active ingredient, sildenafil citrate, is licensed for the same use and follows the same dosing [1, 5].

Other manufacturers could make a generic version once Pfizer's patent on Viagra expired in the UK in 2013 [10]. The difference between Viagra and sildenafil generics is mostly in how the tablet looks: one UK generic is a white, round tablet rather than a blue diamond [1, 5].

Who should not take it

Some combinations are dangerous. Don't take sildenafil if you:

• use nitrates in any form, such as GTN for chest pain, or amyl nitrite ("poppers"), because together they can cause a dangerous drop in blood pressure
• take riociguat
• have been told sexual activity isn't advisable, for example because of unstable angina or severe heart failure
• have recently had a heart attack or stroke, or have low blood pressure (below 90/50 mmHg)
• have severe liver problems, an inherited retinal condition such as retinitis pigmentosa, or have lost vision in one eye from non-arteritic anterior ischaemic optic neuropathy (NAION) [1, 3]

Recreational drugs such as cocaine, amphetaminesand ecstasy may increase cardiovascular risks when used with Sildenafil [1, 3].

Sildenafil from a pharmacy without prior medical consultation may not be suitable and is not recommended for men who experience chest pain or marked breathlessness during moderate physical activity, such as brisk walking or climbing two flights of stairs. They should always seek medical advice before usind it. Sildenafil also shouldn't be combined with other ED treatments [1, 4].

Common side effects

   

Headache is the most common side effect, affecting one in ten people or more. Flushing, indigestion, a blocked nose, dizziness, nausea and changes in vision, such as blurred vision or a blue tinge, are also common, and the NHS lists stomach ache, diarrhoea and anxiety too. If you're dizzy or your vision is blurred, don't drive or use machinery. In trials, few men stopped sildenafil because of side effects, at a rate similar to placebo [1, 3].

The blue tinge can occur because sildenafil also affects an enzyme called PDE6, an enzyme the retina uses to process light. This plays a role in how the eye detects light and colour. After a 100 mg dose, some people had mild difficulty telling blue from green at one hour, with no effect by two hours [1].

Sudden vision loss is rare but serious. NAION, vision loss from reduced blood flow to the optic nerve, has been reported with PDE5 inhibitors, and UK product information states that observational data suggest an increased risk [6, 7]. The evidence isn't settled: a 2018 meta-analysis found no significant overall increase within a month of use (relative risk 1.16, 95% CI 0.98 to 1.39), though separate sildenafil and tadalafil analyses showed a link, and the authors couldn't control for confounding [11]. If your sight suddenly changes, stop taking it and get medical help straight away [1].

Call 999 if you think you're having a severe allergic reaction, a heart attack or a seizure, and NHS 111 for other serious side effects [3].

Frequently asked questions

Is Viagra the blue pill?

Usually, yes. Prescription Viagra and pharmacy Viagra Connect are both blue, diamond-shaped tablets. Generic sildenafil is the same medicine but can look different, such as a plain white tablet [1, 4, 5].

Can you get it without a prescription?

Yes. Sildenafil 50 mg can be bought from a pharmacy after speaking with a pharmacist, although men with certain heart, liver or kidney conditions, or who take some other medicines, should see a doctor first [3, 4]. 

Embarrassment is understandable, but it's exactly what illegal sellers rely on, the MHRA warns. Avoid social media, messaging apps and unknown websites: between 2021 and 2025, the MHRA seized about 19.5 million doses of illegally traded erectile dysfunction medicines, which can contain no active ingredient, the wrong dose or hidden drugs. Use a UK-registered pharmacy [2].

Does it work without arousal?

No. Sildenafil helps the blood vessels in the penis relax, making it easier for blood to flow in.  Sexual stimulation is still needed to trigger the process that leads to an erection [1].

Are herbal blue pills the same thing?

No, and some contain undeclared prescription drugs. In a laboratory analysis of 158 sexual enhancement supplements sold in the United Arab Emirates, 13.9% contained hidden sildenafil, tadalafil or vardenafil, and several provided more sildenafil per recommended daily dose than a standard 50 mg tablet. Hidden sildenafil carries the same risks as the licensed medicine, including the dangerous interaction with nitrates, without a label to warn you [1, 12].

Is Viagra Connect the same as the blue pill?

It's the same medicine, sildenafil 50 mg in a blue, diamond-shaped tablet. It was first authorised for pharmacy sale in November 2017 and is limited to one tablet a day. Its rules are stricter in places; for example, it mustn't be taken with the HIV medicine ritonavir. On prescription, a doctor can adjust the dose to 25 mg or 100 mg [1, 3, 4].

Is Kamagra the same as Viagra?

No. Kamagra isn't licensed in the UK, and the MHRA has prosecuted people for supplying it [13]. With any unlicensed ED pill, there's no way to check what it contains: illegally traded ED medicines seized in the UK have been found with no active ingredient, the wrong dose or hidden drugs [2].