Looking to buy Sildenafil online? Sildenafil citrate is a clinically proven treatment for erectile dysfunction (ED). It works by increasing blood flow to the penis, so you can get and keep an erection when you're sexually aroused. It won't increase your libido or treat any underlying cause of ED, but for many people with ED, it's an effective way to manage symptoms.
To buy Sildenafil through IQ Doctor, you'll first complete a short online consultation. This lets one of our UK-registered prescribers check it's a suitable treatment for you before anything is dispensed.
What is Sildenafil?
Sildenafil tablets contain the same active ingredient (Sildenafil citrate) as Viagra, but cost less.
Sildenafil citrate improves blood flow to the penis. When you're sexually stimulated, it helps you get a firmer erection that lasts longer.
Sildenafil won't improve your libido or resolve any underlying physical causes of your ED.
Sildenafil is prescribed for adult men, or people assigned male at birth, with erectile dysfunction. Whether it's suitable for you depends on your medical history, the medicines you take and the underlying cause of your ED. Our clinical team reviews every consultation individually, so we only recommend treatment when it's the right fit for you.
What is the best Sildenafil dosage?
The typical dose of Sildenafil is 50mg.
You may be prescribed a lower dose of 25mg or a higher dose of 100mg instead. This depends on your age and the cause and severity of your ED.
The dose has no bearing on how soon the treatment starts to work or how long it lasts.
Doses above 100mg are generally not prescribed, as they have a higher risk of causing side effects.
Is Sildenafil comparable to Viagra?
Sildenafil has the same active ingredient as Viagra and works in the same way to treat erectile dysfunction. Both medicines have the same strength at an equivalent dose.
How to use Sildenafil
Take one Sildenafil tablet an hour before sex.
It works better if you take it on an empty stomach and when you're not under the influence of alcohol.
Don't take more than one tablet in 24 hours, and don't take it with any other ED medicines.
How to get Sildenafil
Complete a short online questionnaire about your health, medical history and treatment goals. This helps our clinical team understand your circumstances and identify what's suitable for you.
A UK-registered prescriber then reviews your answers. They check for anything that might affect your suitability, such as other medicines you take or existing health conditions, before approving treatment and confirming the most appropriate dose.
Once your prescriber has approved treatment, your Sildenafil tablets are dispensed by our pharmacy, which is registered with the General Pharmaceutical Council (GPhC). Orders are dispatched the same day and delivered free of charge anywhere in the UK, in discreet, unbranded packaging. Our UK-based clinical team is here to support you throughout your treatment, free of charge.
Start your online consultation today.
Side effects of Sildenafil
Possible side effects include:
Nausea
Vomiting
Back discomfort
Diarrhoea
Allergic rash
Facial flushing
Headaches
Lightheadedness
Nasal congestion
Indigestion
Palpitations (a pounding or noticeable heartbeat)
Blurred vision
Warnings of use
If you're taking an alpha-blocker (such as doxazosin or tamsulosin), wait at least 6 hours before taking Sildenafil.
If you're taking nicorandil or nitrates to treat angina, such as GTN (glyceryl trinitrate) spray or isosorbide mononitrate tablets, do not take Sildenafil.
Tell your doctor about any medicines you take, whether prescription, over-the-counter, recreational or otherwise, so they can check Sildenafil is suitable for you.
Speak to our clinical team if you experience anything that concerns you, or if symptoms persist.
How does Sildenafil work?
Sildenafil increases blood flow to the soft tissue of your penis. This makes it easier to get and keep an erection.
Is Sildenafil safe?
Sildenafil is generally a well-tolerated and effective ED treatment for adult men of any age. It's a prescription-only medicine, so only your doctor can decide if it's a suitable treatment for you.
How long does Sildenafil take to work?
Sildenafil usually starts to work 30 to 60 minutes after you take it. It can take longer to start working if you take it with a heavy meal.
The fattier the meal, the longer Sildenafil will take to start working. For best results, take Sildenafil an hour before you plan to have sex, and try to take it on an empty stomach.
How long do the effects of Sildenafil last?
Sildenafil can help you get an erection for up to 4 hours after you take it, when you're sexually aroused. Your erection will go away after sex.
Is it true that Sildenafil makes you last longer during sex?
Sildenafil helps you keep an erection long enough for successful sex. As a result, you should expect your erection to last longer.
When does Sildenafil not contribute to an erection?
If Sildenafil doesn't give you an erection, it might be because of:
Not being sexually aroused
Not waiting long enough after taking it before having sex (it usually takes 30 to 60 minutes to start working)
Waiting too long after taking it to have sex (it usually works for up to 4 hours)
Not taking a high enough dose for an erection
A psychological cause of ED, such as problems with sexual arousal or confidence
What is considered a 'standard' dose of Sildenafil?
Sildenafil comes in different doses. The lowest dose is 25mg and the highest is 100mg.
Your doctor will decide the right dose for you. Men with mild to severe ED commonly benefit from a 50mg dose.
What side effects does Sildenafil have?
Sildenafil is generally well tolerated. Some common side effects include nasal congestion, headaches and muscle aches.
How often is it safe to take Sildenafil?
Sildenafil is meant to be taken as needed, about an hour before you plan to have sex.
Don't take more than one dose in any 24-hour period.
If you'd like a longer-acting ED treatment, talk to your doctor about switching to an erectile dysfunction medicine that lasts longer, such as Cialis (Tadalafil).
Can Sildenafil be purchased over the counter?
Sildenafil is a prescription-only medicine, so you need a doctor's prescription before you can buy it from a pharmacy.
Viagra Connect is a brand of Sildenafil you can buy over the counter without a prescription. It only comes in 50mg tablets.
Is Sildenafil unsafe to take with other medications?
Don't take Sildenafil if you take any medicines known as nitrates. Taking Sildenafil with nitrates can cause a sudden, severe drop in blood pressure, which is a serious health risk.
If you take nitrates, tell your doctor when you discuss Sildenafil for ED. Your doctor should also know about any other medicines you take.
Should you avoid any food or drink while taking Sildenafil?
You can eat and drink while taking Sildenafil. A heavy or fatty meal can make it slower to start working, and it works better when you're not under the influence of alcohol.
Are there other treatment options for erectile dysfunction?
You can use Sildenafil on its own, or combine it with lifestyle changes to lower your chances of ED coming back.
Simple lifestyle changes that can improve ED include:
Keeping a healthy body mass index (BMI)
Stopping smoking
Stopping or cutting down on alcohol
Avoiding recreational drugs
Exercising daily
Reducing stress in your daily life
Our Clinical Authors
This page has been written by a registered UK pharmacist and reviewed by our clinical team to ensure it is accurate, clear and reflects current clinical guidance.
Last medically reviewed: 06 November 2026
Last updated: 06 November 2026