Safety information · Internal patient-safety page
Sildenafil safety summary
Sildenafil treats erectile dysfunction by relaxing blood vessels in the penis so blood flow can support an erection during sexual stimulation. It does not cause an erection on its own and does not increase sexual desire.
What it's used for
- Standard starting dose is 50 mg taken on demand, no more than once per day.
- Effect lasts up to 4 hours; sexual stimulation is still required for the medicine to work.
- A heavy or fatty meal can delay onset. Taking it on a lighter stomach gives a more predictable response.
Most common side effects
- Headache: the single most common effect.
- Facial flushing and a feeling of warmth.
- Indigestion, nausea or stomach discomfort.
- Stuffy or runny nose, dizziness.
- Visual changes: blue tinge, light sensitivity, blurred vision (transient).
Serious side effects: stop and seek care
- Erection lasting more than 4 hours (priapism): go to A&E to avoid permanent tissue damage.
- Sudden loss or decrease in vision in one or both eyes.
- Sudden hearing loss or ringing in the ears.
- Chest pain during or shortly after sexual activity: call emergency services.
- Severe allergic reaction (rash, swelling, difficulty breathing).
Who should not take it
- You take any nitrate medicine (for chest pain / angina) or amyl-nitrite recreational drugs (“poppers”): the combination can cause life-threatening blood-pressure drops.
- You take riociguat (for pulmonary hypertension) or any other guanylate-cyclase stimulator.
- Recent heart attack, stroke or unstable angina in the last 6 months.
- Severe liver impairment, severe low blood pressure, or known hereditary degenerative retinal disorders.
- You have ever had non-arteritic ischaemic optic neuropathy (NAION).
Interactions to flag
- Alpha-blockers (used for high blood pressure / prostate): risk of dizziness when standing.
- Strong CYP3A4 inhibitors such as ritonavir, ketoconazole, itraconazole, erythromycin, clarithromycin: dose may need to be lowered.
- Other ED treatments: never combine sildenafil with another PDE5 inhibitor (tadalafil, vardenafil, avanafil).
- Alcohol: large amounts worsen side effects and reduce effectiveness.
- Grapefruit juice can increase blood levels, best avoided.
Message us in the app chat if you notice any of these
- Side effects that don't settle after a few hours, or that affect daily life.
- An erection that won't go down, sudden vision or hearing changes. These are A&E events first, then message us.
- A new medication or recreational substance you've started since your consultation.
AEMPS CIMA: Sildenafil
Back to your consultationThis page summarises information from the regulator-approved leaflet for reference only. It is not medical advice and does not replace the assessment of an EU-licensed doctor. Your doctor will review your individual history, dose and interactions during your consultation.