Viagra (Sildenafil) Adverse Effects
The most common adverse effects of Viagra are headache, flushing, rhinitis (nasal congestion), and dyspepsia, which occur in a dose-dependent manner and are generally mild to moderate in severity. 1
Common Adverse Effects (Occur Frequently)
The following adverse effects are extensions of sildenafil's pharmacologic mechanism as a PDE5 inhibitor and occur more frequently than placebo:
- Headache (16% vs 4% placebo) - the most frequently reported adverse effect 2
- Flushing (10% vs 1% placebo) - facial redness and warmth 2
- Nasal congestion/rhinitis - stuffy or runny nose 1
- Dyspepsia (7% vs 2% placebo) - indigestion or upset stomach 1, 2
These effects are predominantly transient and mild to moderate in nature, reflecting the vasodilatory mechanism of the drug. 2
Less Common Adverse Effects
The following occur less frequently but are still documented:
- Visual disturbances - including color vision changes (blue tinge), blurred vision 1
- Myalgia - muscle pain 1
- Nausea 1
- Diarrhea 1
- Vomiting 1
- Dizziness 1
- Chest pain 1
- Back pain 1
Serious Adverse Effects (Rare but Important)
Vision Loss (NAION)
- Nonarteritic anterior ischemic optic neuropathy (NAION) - sudden decrease or loss of vision in one or both eyes 1, 3
- Among 4 million veterans aged ≥50 years, PDE5 inhibitors were NOT associated with increased risk for NAION (RR 1.02,95% CI 0.92-1.12), but WERE associated with increased risk for "possible NAION" (RR 1.34,95% CI 1.17-1.55) 1
- If sudden vision loss occurs, discontinue immediately and seek medical attention 3
Hearing Loss
- Sudden decrease or loss of hearing - rare but documented in postmarketing surveillance 1, 3
- Patients should be instructed to stop the medication and contact their physician immediately if this occurs 3
Cardiovascular Events
- Hypotension - particularly when combined with nitrates (see contraindications below) 3
- Heart attack, stroke, irregular heartbeats, and death - most occurred in men who already had underlying heart problems 3
- Serious cardiovascular events occur at rates <2% with no difference between sildenafil and placebo in controlled trials 1
Priapism
- Prolonged erection lasting >4 hours - reported infrequently in postmarketing surveillance but not in clinical trials 1
- No cases of priapism were reported in clinical trials of >3700 patients 2
- Requires immediate medical attention if erection lasts >4 hours 3
Pediatric-Specific Adverse Effects
In children treated for pulmonary hypertension:
- Headache, nasal congestion, flushing, agitation, hypotension 1
- Vision and hearing loss - particular concerns in pediatric population 1
- Priapism - documented risk 1
- Increased mortality risk - higher doses in children with IPAH showed greater mortality in the STARTS-2 study; avoid high-dose sildenafil monotherapy in children 1
- Retinal concerns - delay use in extremely preterm infants until retinal vascularization is established 1
Absolute Contraindication
Concurrent use of nitrates in any form (nitroglycerin, isosorbide dinitrate) is an absolute contraindication - this combination can cause severe, potentially fatal hypotension. 1, 3
Discontinuation Rates
- Only 2.5% of patients discontinued sildenafil due to adverse events (comparable to 2.3% for placebo) in double-blind trials 2
- In long-term open-label studies, 90% of patients completed treatment with only 2% withdrawing due to adverse events 2
- The low discontinuation rate reflects the generally favorable tolerability profile of sildenafil 2
Clinical Context
Most adverse effects are transient, mild to moderate, and dose-dependent. 1, 2 The incidence of serious adverse events is <2% and does not differ significantly from placebo. 1 Adverse event profiles are similar across all PDE5 inhibitors (sildenafil, tadalafil, vardenafil). 1