Sildenafil is the active ingredient originally marketed as Viagra by Pfizer. It belongs to a class of medicines called PDE5 inhibitors, which work by increasing blood flow to the penis when a man is sexually aroused. Since the patent expired in 2013, generic sildenafil has become widely available across the UK at a fraction of the branded price.
How Does Sildenafil Work?
During sexual stimulation, the body releases nitric oxide in the erectile tissue of the penis. Nitric oxide activates an enzyme that produces cyclic GMP (cGMP), which relaxes smooth muscle and allows blood to flow into the penis. Sildenafil blocks the enzyme PDE5 that breaks down cGMP, helping to maintain an erection.
Sildenafil does not cause an erection on its own — sexual arousal is still required for the medication to work.
Who Can Take Sildenafil?
Sildenafil is suitable for most adult men with erectile dysfunction. However, it is not recommended if you:
- Take nitrate medications for chest pain (e.g. GTN spray)
- Have severe heart or liver problems
- Have recently had a stroke or heart attack
- Have low blood pressure (hypotension)
- Take alpha-blockers for prostate conditions without medical advice
How to Take It
The standard starting dose is 50 mg, taken approximately one hour before sexual activity. Depending on effectiveness and side effects, your prescriber may adjust the dose to 25 mg or 100 mg. Do not take more than one dose in 24 hours.
High-fat meals can delay absorption, so sildenafil is best taken on an empty or light stomach.
Getting Sildenafil in the UK
In the UK you can obtain sildenafil in several ways:
- NHS prescription — available from your GP, though prescribing criteria may vary by area
- Private prescription — from a registered prescriber or online pharmacy regulated by the GPhC
- Over the counter — Viagra Connect (50 mg sildenafil) is available from pharmacies without a prescription following a pharmacist consultation
Always ensure any online pharmacy you use displays the GPhC internet pharmacy logo and is listed on the GPhC register.