If you sometimes have issues getting or keeping an erection, you may be experiencing ED. Sildenafil's active ingredient (sildenafil citrate) increases blood flow to the penis. It enables a firmer, longer-lasting erection if you are sexually aroused. 

The effects of Sildenafil can last for up to six hours. However, how long the effects last depends on your age, health and dosage.

The treatment will not resolve the underlying physical cause of your erectile dysfunction or increase your sexual desire.

Sildenafil normally starts to work within 25-60 minutes. But don’t forget, you need to be aroused for it to work.   

It’s thought that Sildenafil works for as many as two thirds of men. If you have eaten a large meal or drunk more than 1-2 units of alcohol, you may find Sildenafil is less effective.

There’s also a chance it might not work if it’s your first-time taking Sildenafil. We recommend you try an ED medication up to 8 times on separate occasions before giving up, considering a higher dose or seeking an alternative like tadalafil.

Take one Sildenafil tablet an hour before sex. Sildenafil works best on an empty stomach.

Sildenafil can be taken once a day. You should never take more than one Sildenafil tablet in 24 hours. You should not split the Sildenafil tablets or combine Sildenafil with other ED medicines.

The standard dose is 50mg. Depending on your age, height and weight, the cause and the severity of your ED, you may be prescribed a lower dose of 25mg, or a higher one of 100mg. Higher doses come with an increased chance of developing side effects. 

Sildenafil dosage does not affect how quickly or for how long the treatment works. You should take Sildenafil tablets in the dosage suggested by your clinician or as explained in the patient information leaflet. 

Side effects are uncommon, but can include:

• Nausea
• Vomiting
• Back pain
• Diarrhoea 
• An allergic rash
• Facial flushing
• Headaches
• Light headedness
• Nasal congestion
• Indigestion
• Palpitations (racing heartbeat) 

Sildenafil side effects can include vision changes. This is rare, however if you experience a sudden decrease or loss of vision, you should call your doctor or 111 straight away.

For full information on side effects and correct use, see the patient information leaflet. 

Most men over the age of 18 can take Sildenafil. However, if you are taking nicorandil or nitrates, such as GTN spray or isosorbide mononitrate tablets to treat angina you won’t be able to use Sildenafil. If you are taking alpha-blockers (such as doxazosin or tamsulosin), you should wait at least 6 hours between taking those and taking Sildenafil.

It is important that you let us know which prescription, over-the-counter medicines and recreational drugs you are taking so that we can prescribe Sildenafil safely. Please note women can’t take sildenafil. 

Sildenafil helps you to keep an erection long enough to have successful sex. So, it can help you keep your erection longer. We often recommend those who have ED and premature ejaculation (PE) to use ED medications before trying PE alternatives (Priligy and EMLA) as it may also improve their PE. But these ED medications wouldn't be used to treat PE if you are not also experiencing ED.

Sildenafil works in the same way as Viagra. With the same active ingredient, they treat ED in the same way. When the dosage is the same, both medications are the same strength.

It’s a good idea to try an ED medication as many as 8 times before you make a judgement on if it’s working for you. If after this time you don’t think it is working, speak to your clinician and they may advise changing the dosage or trying something else.

If Sildenafil stops working for you, you should speak to your clinician.

Sildenafil can be accessed with or without a prescription online or from a pharmacy. You can request and pay for Sildenafil online, you don’t necessarily need a prescription. If you choose to buy Sildenafil over the internet, make sure that any online pharmacy is registered with the General Pharmaceutical Council (GPhC), any online doctor service is regulated by the Care Quality Commission (CQC) and all doctors are registered with the General Medical Council (GMC).

Sildenafil is also the active ingredient in Viagra Connect, an ED treatment that doesn't require a prescription. However, you will need to answer some questions to confirm your suitability for the treatment. Using our service, you can complete a quick online consultation.