Sildenafil: Uses, Strengths, Side Effects & Safety
Sildenafil is a medicine used to treat erectile dysfunction (ED), a condition involving difficulty achieving or maintaining an erection. It belongs to a class of medicines known as phosphodiesterase type 5 (PDE5) inhibitors.
This guide explains how sildenafil works, its commonly authorised strengths, possible side effects, important interactions and the differences between medicines authorised in the United Kingdom and products marketed internationally.
What Is Sildenafil?
Sildenafil is the active ingredient in Viagra and various generic medicines used to treat erectile dysfunction. It works by temporarily inhibiting the PDE5 enzyme, helping blood vessels in the penis relax and increasing blood flow during sexual stimulation.
Sildenafil does not automatically produce an erection and does not increase sexual desire. Sexual stimulation is still required for its erectile effects.
What Strengths Does Sildenafil Come In?
For erectile dysfunction, sildenafil tablets authorised in the UK commonly contain 25mg, 50mg or 100mg of sildenafil.
The appropriate strength depends on factors including medical history, individual response, other medicines and possible adverse effects. The usual maximum recommended dose for erectile dysfunction is 100mg once daily.
Some products marketed internationally carry labels stating strengths above 100mg. These should not be interpreted as established safe or recommended doses for erectile dysfunction. Higher exposure can increase the risk of adverse effects.
How Long Does Sildenafil Take to Work?
Sildenafil commonly begins working within 30 to 60 minutes, although the onset varies between individuals. A high-fat meal may delay its effects.
Its effects typically remain relevant for several hours, but this does not mean an erection should last continuously during that period.
How Long Does Sildenafil Last?
Sildenafil’s effects are commonly described as lasting approximately four hours, although the duration varies. Age, metabolism, health conditions and other medicines can influence how the body processes sildenafil.
What Are the Possible Side Effects?
Common side effects of sildenafil may include:
- Headache
- Facial flushing
- Indigestion
- Nasal congestion
- Dizziness
- Temporary visual disturbances
Serious adverse effects are less common but require prompt attention. Seek urgent medical assistance for chest pain, sudden loss of vision or hearing, or a prolonged or painful erection.
Important Medicine Interactions
Sildenafil must not be combined with nitrate medicines, commonly prescribed for certain heart conditions, or recreational nitrites known as poppers. Combining these substances can cause a dangerous fall in blood pressure.
Sildenafil also has important interactions with riociguat and certain other medicines. People taking alpha-blockers, some antifungal medicines, antibiotics or HIV treatments may require additional medical assessment.
Sildenafil and Alcohol
Excessive alcohol consumption can contribute to erectile difficulties and may increase dizziness or other unwanted effects associated with sildenafil.
Sildenafil Tablets and Oral Jelly Formulations
Sildenafil is commonly supplied in authorised tablet formulations. Other products marketed internationally include oral jelly preparations.
Different dosage forms are not automatically interchangeable. Their quality, absorption characteristics and regulatory approval may differ.
Sildenafil, Viagra and Kamagra: What Is the Difference?
Viagra is a branded medicine containing sildenafil. Generic sildenafil medicines contain the same active ingredient and, when authorised by the relevant regulator, must meet applicable standards for quality, safety and efficacy.
Kamagra is a separate product brand marketed internationally. Although Kamagra products are labelled as containing sildenafil, Kamagra does not have UK marketing authorisation and should not be described as an authorised generic version of Viagra.
Is Sildenafil Legal in the UK?
Sildenafil is used in medicines authorised in the United Kingdom. Depending on the specific product and applicable pharmacy requirements, authorised sildenafil medicines may be supplied on prescription or following an appropriate pharmacy assessment.
However, authorisation applies to individual medicinal products, not simply to an active ingredient. A product containing sildenafil is not automatically authorised for UK supply.
When Should Someone Seek Medical Advice?
Persistent erectile dysfunction can sometimes be associated with underlying conditions, including cardiovascular disease, diabetes or other health problems.
Anyone experiencing persistent symptoms should consult an appropriately qualified healthcare professional. Medical advice is particularly important for people with heart conditions, low blood pressure or complex medication histories.
Frequently Asked Questions
Is sildenafil the same as Viagra?
Sildenafil is the active ingredient in Viagra. Viagra is a brand name, while sildenafil is also available in other authorised medicines.
Can sildenafil be taken every day?
The appropriate frequency depends on the prescribed treatment and individual medical circumstances. For erectile dysfunction, sildenafil is generally taken as needed and should not be taken more than once daily.
Does a higher strength always work better?
No. A higher strength does not guarantee better results and may increase adverse effects. Treatment should follow the dosing recommendations for the authorised medicine and the advice of a qualified healthcare professional.
Is Kamagra an authorised generic Viagra in the UK?
No. Kamagra is not authorised as a medicine in the UK. It should not be confused with generic sildenafil medicines that have UK marketing authorisation.
Sildenafil Compared With Tadalafil
Sildenafil and tadalafil are both PDE5 inhibitors used to treat erectile dysfunction, but they differ in duration of action, dosing schedules and certain side effects. For a detailed comparison, read our Sildenafil vs Tadalafil Guide.
Further Information
For independent medical guidance, consult the NHS sildenafil information pages.
Information about UK medicines regulation is available from the Medicines and Healthcare products Regulatory Agency (MHRA).
This article is provided for general educational purposes and is not a substitute for individual medical advice.