Sildenafil

Is sildenafil safe?

For most men who can safely have sex, yes. Sildenafil, sold as Viagra for erectile dysfunction and Revatio for pulmonary arterial hypertension (PAH), has been on the market since 1998. Its common side effects are a headache, flushing and indigestion that pass within hours. Overdoses are rarely dangerous.

The big exception is nitrates. Taken with nitroglycerin, isosorbide or recreational 'poppers', sildenafil can drop blood pressure to a dangerous level. The second risk is not the drug itself but where it comes from: fake pills and 'natural' supplements spiked with unknown amounts. We score sildenafil 81, level with finasteride (81).

What dose of sildenafil is safe?

The US label doses:

Use	Dose
Erectile dysfunction (Viagra)	50 mg about 1 hour before sex (anywhere from 30 minutes to 4 hours); 25 to 100 mg; no more than once a day
Over 65, liver cirrhosis, severe kidney disease	Consider starting at 25 mg
Taking an alpha-blocker	Stable on the alpha-blocker first, then start at 25 mg
Taking ritonavir	25 mg, no more than 25 mg in 48 hours
PAH in adults (Revatio)	20 mg three times a day, up to 80 mg three times a day
PAH in children 1 to 17 (Revatio)	10 mg three times a day up to 20 kg; 20 mg three times a day above

In the UK, the MHRA agreed in November 2017 to let pharmacies sell Viagra Connect 50 mg without a prescription to men 18 and over, after a pharmacist check.

Why nitrates and sildenafil don't mix

Sildenafil works by relaxing blood vessels. Nitrates do the same through the same chemical pathway, and together the effect multiplies. The label contraindicates nitrates "in any form", taken regularly or now and then, and says it is unknown when after a sildenafil dose a nitrate could be safely given. That matters in an emergency: anyone with chest pain should tell paramedics if they have taken sildenafil.

Riociguat, a lung blood pressure drug, is also ruled out. Other combinations need care rather than a ban: alpha-blockers for prostate or blood pressure (doxazosin, tamsulosin), other blood pressure drugs such as amlodipine, and alcohol all add to the drop in blood pressure. Ritonavir raised sildenafil levels 11-fold in studies, and erythromycin, ketoconazole and itraconazole about 3-fold.

Rare but serious: vision, hearing and priapism

Vision. Sudden loss of vision in one or both eyes can be a sign of NAION, a stroke-like loss of blood flow to the optic nerve. The label puts the background rate at 2.5 to 11.8 cases per 100,000 men over 50 a year; two observational studies found about double the risk shortly after a PDE5 inhibitor dose, though causation is not proven. Men who have had NAION before are at higher risk. A temporary blue tint or light sensitivity is more common, reported by 11% on 100 mg.

Hearing. Sudden hearing loss, sometimes with ringing or dizziness, has been reported. The label says to stop and seek prompt care.

Priapism. An erection lasting more than 4 hours needs emergency treatment; left alone it can cause permanent damage. Men with sickle cell disease, leukaemia, multiple myeloma or a penis deformity such as Peyronie's disease should take care.

The heart. Sex itself puts strain on the heart. The label says sildenafil should not generally be used by men for whom sex is inadvisable, and there are no trial data in men who had a heart attack or stroke in the last 6 months.

Fake Viagra and spiked supplements

Sildenafil is one of the most counterfeited medicines. The FDA's tainted sexual enhancement list runs to hundreds of notices since 2012, with 30 in 2026 alone by late September. A typical case: in September 2026 the FDA found sildenafil and tadalafil, neither on the label, in a product sold as MAXMAN Coffee. Others came as honey sachets, sweets and capsules. In a 2024 UK case prosecuted by the MHRA, a dealer sold sildenafil on Amazon and eBay as a "100% natural remedy"; officers found 97,000 tablets at one address, from erectile dysfunction products to controlled drugsControlled substanceA medicine or drug that the law restricts because it can be misused or cause dependence. Countries group them into schedules or classes.More in the glossary.

The danger is twofold: an unknown dose, and men on nitrates who would never knowingly take sildenafil. Buy only from a pharmacy, and treat 'herbal Viagra', yohimbine blends and 'male enhancement' products with suspicion.

Who should be careful

Talk to your doctor or pharmacist before taking sildenafil if you use any nitrate or riociguat, have heart disease, very low or very high blood pressure, had a heart attack or stroke in the last 6 months, have had NAION or retinitis pigmentosa, have a bleeding disorder or stomach ulcer, or take alpha-blockers, HIV medicines or strong antifungals. Erectile problems can be an early sign of heart disease or diabetes, which is a good reason to see a doctor rather than buying pills online.

How we scored it

Track record (92), overdose marginOverdose marginHow far a normal dose is from a harmful one. A wide margin means an accidental extra dose is unlikely to cause serious harm.More in the glossary (88) and serious side effects (82) are strong. Interactions (58) is the weakest factor: the list is short, but the nitrate combination can be life-threatening. Regulatory warnings (78) reflect label warnings without a boxed warningBoxed warningThe strongest safety warning the US FDA puts on a medicine's label, printed inside a black border at the top.More in the glossary. Counterfeit and spiked products are a real risk but sit outside the score, which rates the licensed drug.