Sildenafil (Generic Viagra) Tablets

Sildenafil is a cost-effective erectile dysfunction medication that contains the same active ingredient as Viagra.

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4 pack of 50mg sildenafil citrate film-coated tablets
Back of a packet containing four 50mg film-coated tablets of Sildenafil
Front of packet containing four 25mg Sildenafil tablets
Packet containing four 100mg film-coated tablets of Sildenafil
Blister pack of four Sildenafil tablets
Close up photo of two white Sildenafil tablets
Packaging picture

Prices from £9.95

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25 mg

4 tablet(s) - £9.95

8 tablet(s) - £17.00

12 tablet(s) - £27.00

16 tablet(s) - £35.00

28 tablet(s) - £49.00

40 tablet(s) - £59.00

64 tablet(s) - £63.55

50 mg

4 tablet(s) - £12.00

8 tablet(s) - £19.00

12 tablet(s) - £28.00

16 tablet(s) - £36.00

28 tablet(s) - £59.00

40 tablet(s) - £79.00

100 mg

4 tablet(s) - £17.00

8 tablet(s) - £26.00

12 tablet(s) - £35.00

16 tablet(s) - £45.00

28 tablet(s) - £75.00

40 tablet(s) - £99.00

What is sildenafil?

Sildenafil is a generic medication used to treat erectile dysfunction. It contains the active ingredient sildenafil, which is the same ingredient in Viagra. Sildenafil is a more affordable option for ED. It can help you get and keep an erection, as long as you are sexually aroused. It comes in tablet form and usually takes 30 to 60 minutes to work.

How does sildenafil work?

Sildenafil works by relaxing your blood vessels to allow more blood to flow to the penis. This blood flow triggers an erection and makes sildenafil an ideal treatment for erectile dysfunction.

Sildenafil blocks PDE-5 (phosphodiesterase type 5) enzymes in your penis to widen your blood vessels. There are other medicines that work in the same way, and these are called ‘PDE-5 inhibitors’.

Generally, you must be sexually aroused for sildenafil to work and give you an erection.

Sildenafil dosage

The usual starting dose is 50mg, but you may be started on a lower dose of 25mg if you take some medications. The highest dose is 100mg, but you should not take more than prescribed.

How to take sildenafil

For best results, you should take sildenafil 1 hour before having sex. The effects of sildenafil can last for up to 4 to 5 hours.

Do not take more than 1 sildenafil tablet a day. Swallow it whole without chewing or crushing it. A glass of water will help you swallow it but you do not need to take it with food.

To help get the best results when taking sildenafil:

  • avoid drinking grapefruit juice
  • only have small amounts of alcohol (up to 3 units per day), as having a large amount of alcohol might make it difficult to get an erection
  • take sildenafil on an empty stomach, as eating before taking sildenafil can make it work slower

If you have taken sildenafil and still cannot get an erection, do not take another dose. Try again the next day and make sure you avoid fatty foods and alcohol.

Erectile dysfunction can sometimes be caused by an underlying health reason, so speak to your doctor about a health check and other options if sildenafil does not work.

Side effects

You might have some side effects when taking sildenafil, but most of the time they should be minor.

Common side effects of taking sildenafil include:

  • nausea (feeling sick)
  • headaches
  • indigestion
  • hot flushes
  • dizziness
  • stuffy nose
  • blurry vision

If you experience side effects that are uncomfortable or do not get better with time, you should speak to a doctor.

Uncommon side effects of taking sildenafil include:

  • skin reactions, such as peeling or swollen skin
  • seizures
  • a painful erection that lasts over 4 hours
  • chest pain
  • changes in eyesight

If you experience any of these symptoms, stop taking sildenafil immediately and contact your doctor or call 999. For further information on very rare side effects, check the patient information leaflet contained in your medication packet or online.

You should also call 999 or go to A&E if you have a rare allergic reaction to sildenafil, where you may get these symptoms:

  • wheezing
  • tightness in your chest or throat
  • trouble talking or breathing
  • skin rash, such as red or itchy skin
  • swelling of your face, lips, mouth, tongue or throat

Who can take sildenafil

You may be able to take sildenafil if you are over 18 years old and have erectile dysfunction.

You should not take sildenafil if you:

  • are taking medication for chest pain (nitrates)
  • ever had an allergic reaction to sildenafil or Viagra
  • have low blood pressure
  • have heart or kidney problems
  • have recently had breast cancer or a stroke
  • have a rare inherited eye disease

You should be careful about taking sildenafil and speak to a doctor first if you have:

  • a stomach ulcer
  • bleeding problems, or haemophilia
  • sickle cell anaemia
  • multiple myeloma
  • any deformities in your penis, such as Peyronie's disease (curved penis)

Tell your doctor if any of these apply to you, to make sure that sildenafil is right for you.


Some medications can interact with sildenafil, which could make it less effective or unsafe for you to take. Speak to your doctor if you take any medications, especially:

  • any medication to treat chest pain, such as nitrates
  • nitric oxide donors, such as amyl nitrite
  • riociguat, which is a treatment for chronic thromboembolic pulmonary hypertension
  • protease inhibitors, you may need to be started on a lower dose of 25mg
  • alpha blockers, which can be used for high blood pressure

You may need to avoid alcohol whilst taking sildenafil, as it can affect how well it works. If sildenafil is not working for you or you get side effects like dizziness, do not drink alcohol. You should also avoid drinking grapefruit juice when you take sildenafil.

Alternative treatment for ED

Sildenafil may not be suitable for you or you may need a different treatment for your ED symptoms. You can get alternative erectile dysfunction treatments such as:

  • tadalafil, a generic ED medication containing the active ingredient tadalafil
  • Cialis, a branded version of tadalafil
  • Levitra, which contains the active ingredient vardenafil
  • Spedra, which contains the active ingredient avanafil
  • Viagra, the branded version of sildenafil

You can also get an erectile dysfunction trial pack that contains 3 treatments. This allows you to try different ED treatments to see which works best for you.

Medically reviewed by:
Dr Babak Ashrafi Clinical Lead for Service Expansion

Babak studied medicine at King’s College London and graduated in 2003, having also gained a bachelor’s degree in Physiology during his time there. He completed his general practice (GP) training in East London, where he worked for a number of years as a partner at a large inner-city GP practice. He completed the Royal College of GPs membership exam in 2007.

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Last reviewed: 29 Jul 2022

ZAVA offers a convenient and discreet service to help men improve their erectile dysfunction. There are a number of treatments you can consider. Continue to our erectile dysfunction service page to learn about the treatment options available.

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