What is sildenafil?
Sildenafil is a treatment for erectile dysfunction, often referred to as ED. With the Online Doctor erectile dysfunction service, our clinicians can prescribe Sildenafil if you’re medically suitable.
How does sildenafil work?
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.
Sildenafil is a phosphodiesterase type-5 (PDE-5) inhibitor. PDE-5 is an enzyme that breaks down cGMP, a chemical released in the body when aroused that relaxes the muscle cells in the penis and allows blood flow to increase (causing erections). As ‘inhibitor’ implies, sildenafil stops PDE-5 from working properly and increases blood flow to the penis. This should allow you to get and maintain an erection more easily.
The treatment will not resolve the underlying physical cause of your erectile dysfunction or increase your sexual desire.
How long does it take for sildenafil to take effect?
Sildenafil normally starts to work within 25-60 minutes. But don’t forget, you need to be aroused for it to work.
How long does Sildenafil last?
The effects of Sildenafil can last for up to six hours. However, how long the effects last depends on your age, health and dosage.
This does not mean that you can expect to have an erection for up to six hours, but that during this time you are more likely to get and maintain an erection.
How effective is sildenafil?
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.
Who can take sildenafil?
Most men over the age of 18 can take Sildenafil. However, you can't take sildenafil if the following applies to you:
- You're a woman
- If you are taking nicorandil or nitrates, such as GTN spray or isosorbide mononitrate tablets to treat angina
- 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.
How to take sildenafil
Sildenafil works best on an empty stomach. Sildenafil can be taken once a day and should be taken between 30 minutes and an hour before sex.
Sildenafil can be taken once a day. You should never take more than one Sildenafil tablet in 24 hours.
Can you take sildenafil alongside other ED medication?
Do not combine sildenafil alongside other ED medication.
As there are several options available for erectile dysfunction treatments available, it can be tempting to combine two like sildenafil and tadalafil together to increase your chances of a successful erection.
Do not do this. Combining treatments can lead to side effects like dangerously low blood pressure and fainting.
If you are unsatisfied with your current erectile dysfunction treatment, speak to your GP first.
Sildenafil dosage
There are three dosages of sildenafil: 25mg, 50mg and 100mg. The treatment is currently available as:
| Dosage / Tablet amount | 4 tablets | 8 tablets | 16 tablets |
| 25mg | £12.99 | £19.99 | £33.99 |
| 50mg | £13.99 | £23.99 | £38.99 |
| 100mg | £19.99 | £38.99 | £44.99 |
| Dosage / Tablet amount | 8 tablets | 16 tablets |
| 50mg | £20.39/month | £33.14/month |
| 100mg | £25.49/month | £38.24/month |
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.
“You may be tempted to choose the highest dosage of Sildenafil to guarantee an erection, but that doesn’t guarantee results. Consult your GP or take one of our online consultations to determine the correct dosage for you. It is recommended you try your current dosage eight times to determine its effectiveness. If there’s been little to no effect after that, talk to your GP about changing dosages.” - Dr Bhavini Shah
Sildenafil side effects
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.
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