What are common immediate side effects of sildenafil and how long do they last?
Executive summary
Sildenafil commonly causes transient vasodilatory and sensory side effects such as headache, facial flushing, indigestion, nasal congestion, and visual changes; these typically begin within 30–60 minutes, peak around 1 hour, and are most noticeable while the drug is active in the body — commonly for about 3–5 hours though detectable pharmacologic effect can persist longer in some individuals (onset: [4]; peak and typical active window: [5]; duration extremes: p1_s7). Serious but rare immediate reactions include prolonged erections (priapism), marked hypotension especially with nitrates, sudden vision or hearing loss, and cardiac symptoms — all of which require urgent medical attention [1] [2] [3].
1. Common immediate effects: headache, flushing, dyspepsia and nasal congestion
Headache and facial flushing are consistently the most frequently reported immediate reactions to sildenafil across clinical summaries and patient reports, often described as mild-to-moderate and dose-related; indigestion (dyspepsia) and nasal congestion are also common and reflect systemic vasodilation and smooth-muscle effects seen in trials and drug monographs (headache/flushing/dyspepsia/nasal congestion: [4]; [3]; [1]1).
2. Sensory disturbances: vision and hearing changes are usually transient but alarming
Transient visual effects — blurred vision, changes in color perception or increased light sensitivity — have been reported and are attributed to PDE inhibition in retinal pathways; these sensory effects are usually short-lived but have prompted warnings because rare cases of sudden loss of vision (NAION) and sudden hearing loss with tinnitus or dizziness have been reported and merit immediate evaluation (visual disturbances and risk of NAION: [6]; sudden vision/hearing loss: [1]; p1_s2).
3. Timing: when side effects begin and how long they last
Sildenafil’s onset of action can occur within about 30 minutes and is commonly taken 30–60 minutes before activity, with peak pharmacologic effect around 1 hour — most acute side effects therefore appear within that window and tend to subside over the next few hours while the drug is active, with a typical symptomatic window of roughly 3–5 hours; pharmacokinetic and clinical resources note that pharmacodynamic effects can sometimes be detectable up to 18 hours, and elimination may be prolonged in liver or kidney impairment or with interacting drugs (onset/peak: [4]; typical active window: [5]; prolonged detectability and impaired clearance: [4]; [1]3).
4. Severity drivers: dose, drug interactions and individual health status
Higher doses increase both incidence and severity of side effects — trials and post-marketing analyses show a dose-response for common adverse events — and co-administration with nitrates, certain antibiotics, antifungals, protease inhibitors or grapefruit juice can raise sildenafil levels or potentiate hypotension, increasing risk of serious reactions; patients with cardiac disease, severe liver impairment, or blood disorders need extra caution because adverse outcomes can be more dangerous in these groups (dose-response and common adverse events: [7]; drug interactions and grapefruit effect: [8]; serious effects in heart disease/liver disease/blood disorders: [1]; [1]3).
5. When to worry: red flags and reporting
An erection lasting 4 hours or more (priapism), sudden loss of vision, sudden hearing loss often with tinnitus or dizziness, chest pain, fainting, or marked shortness of breath are urgent signs that require immediate medical care and stopping sildenafil; regulatory and clinical guidance emphasize prompt reporting of these rare but serious events (priapism and emergency warnings: [1]; sudden vision/hearing loss and cardiac warnings: [2]; p1_s4).
6. Evidence caveats and real-world variability
Clinical trials, product labels and large clinical reviews consistently list the same constellation of common immediate side effects, but some real-world prospective studies suggest incidence rates may differ from early trials and that methodology affects reporting — tolerability is generally good, yet individual responses vary and the literature documents both mild transient complaints and rare severe events, so patient-specific counselling and attention to concomitant medications remain essential (real-world vs trials and incidence reporting: [7]; overall safety summaries: [3]; p1_s7).