De hyppigst rapporterede bivirkninger i kliniske undersøgelser hos sildenafilbehandlede patienter var hovedpine, rødmen, dyspepsi, synsforandringer, næsetilstopning, svimmelhed og synsfarveforvrængning.
The most commonly reported adverse reactions in clinical studies among sildenafil treated patients were headache, flushing, dyspepsia, visual disorders, nasal congestion, dizziness and visual colour distortion.