Sildenafil
Is It Right for You?
A complete guide to Sildenafil — what it treats, how it works, dosages, side effects, and when a clinician may prescribe it following an online consultation.
What Is Sildenafil?
Sildenafil is a medicine used to treat erectile dysfunction (difficulty getting or keeping an erection). It helps achieve an erection in response to sexual stimulation.
It is the active ingredient in Viagra and is also available as a generic. It is taken as a tablet around an hour before sexual activity. A lower-strength version is available from pharmacies after a consultation, while higher strengths are prescription-only.
Sildenafil is available on prescription, with some lower-strength supply through pharmacies in the UK. A licensed clinician can review your suitability and any underlying causes through a telehealth consultation and prescribe it where appropriate.
What Conditions Is Sildenafil Used For?
Sildenafil is mainly used for:
helping men get and keep an erection firm enough for sex when sexually aroused.
often used while any contributing conditions, such as diabetes or heart risk factors, are also addressed.
a different, specialist use of sildenafil at set doses, managed by hospital teams.
Sildenafil must not be taken with nitrate medicines (used for chest pain/angina) or certain other heart medicines, as the combination can cause a dangerous drop in blood pressure.
How Does Sildenafil Work?
An erection happens when blood flows into the penis and is held there. Sildenafil works by blocking an enzyme called PDE5, which normally reduces this blood flow.
By blocking PDE5, sildenafil allows blood vessels in the penis to relax and widen, improving blood flow when you are sexually aroused. This helps produce and maintain an erection.
Importantly, sildenafil only works with sexual stimulation - it does not cause an automatic erection. Its effect starts within about an hour and lasts for several hours.
Dosages & Administration
The correct dose depends on the type and severity of infection, age, weight, and kidney function. Always follow your clinician's instructions. The table below is for general reference only.
Administration Tips
Take one tablet about an hour before sex, and remember it only works with sexual stimulation. Do not take more than one dose in 24 hours.
Avoid large, fatty meals and excess alcohol around your dose, as these can delay or reduce its effect.
Side Effects of Sildenafil
Side effects are usually mild and short-lived, reflecting the way sildenafil widens blood vessels.
- Headache
- Facial flushing
- Indigestion
- Blocked or runny nose
- Dizziness
- Changes to vision such as a blue tinge or light sensitivity
- An erection lasting more than 4 hours (priapism) - seek urgent help
- Sudden loss or decrease of vision
- Sudden loss or decrease of hearing
- Chest pain during sex
- Fainting
- Severe allergic reaction
An erection lasting longer than four hours (priapism) is a medical emergency that can damage the penis. Seek urgent medical help if this happens. Also seek help for sudden vision or hearing loss.
Drug Interactions
Always disclose all prescription drugs, over-the-counter medicines, vitamins, and supplements to your clinician or pharmacist before starting sildenafil.
Sildenafil must not be taken with nitrates (for angina/chest pain) because of the risk of a severe, dangerous fall in blood pressure.
Certain medicines that affect blood pressure or the heart must not be combined with sildenafil.
Used for blood pressure or prostate symptoms, these can add to sildenafil's blood-pressure-lowering effect and cause dizziness.
These can raise sildenafil levels, so a lower dose may be needed; tell your clinician everything you take.
Important Warnings
Because sex is physical activity and sildenafil affects blood vessels, tell your clinician about any heart condition. It may not be suitable if your heart cannot cope with the exertion of sex.
Never combine sildenafil with nitrate medicines or recreational 'poppers', as together they can cause a life-threatening drop in blood pressure.
Erectile dysfunction can be a sign of conditions such as diabetes, high blood pressure, or heart disease. A consultation can help identify and address any underlying cause.
Only obtain sildenafil through legitimate, regulated services. Counterfeit products bought from unverified sources can be ineffective or harmful.
Speak to a Clinician About Treatment
Getting advice no longer means sitting in a waiting room. Through The GP Service, you can consult with a licensed clinician in minutes — from home, on your lunch break, or wherever works for you. If treatment is clinically appropriate, your clinician can issue a prescription during the consultation. A consultation does not guarantee a prescription.
The treatment you need, when you need it.
Sildenafil FAQs
Yes. A licensed clinician can review your health, suitability, and any underlying causes through a telehealth consultation and prescribe sildenafil where appropriate.
Sildenafil is usually taken about an hour before sex. It works for several hours but only produces an erection with sexual stimulation.
It is not automatic. Sildenafil helps you get an erection in response to arousal; without sexual stimulation it will not produce one.
Sildenafil is taken as needed, with no more than one dose in 24 hours. If you want a daily option, discuss alternatives with your clinician.
Both lower blood pressure, and together they can cause a sudden, dangerous drop. If you take nitrates for chest pain, sildenafil is not safe for you.
A small amount of alcohol is unlikely to be a problem, but heavy drinking can make erections harder to achieve and may worsen side effects like dizziness.