Hypersensitivity to sildenafil; concomitant use with nitrates or nitric oxide donors; severe cardiovascular dysfunctions, unstable angina or insufficiency. severe cardiac; I.H. serious; hypotension; recent history of stroke or AMI; retinitis pigmentosa; combination with strong CYP3A4 inhibitors (ketoconazole, itraconazole, ritonavir); patients with loss of vision due to non-arteritic anterior ischemic optic neuropathy regardless of whether or not this episode was associated with previous exposure to a PDE5 inhibitor. Co-administration of PDE5 inhibitors, including sildenafil, with guanylate cyclase stimulators, such as riociguat, is contraindicated as it can potentially cause symptomatic hypotension. Effect inhibited with: strong CYP3A4 inducers, such as carbamazepine, phenytoin, phenobarbital, St. John's wort, and rifampin. Enhanced action and toxicity with: with CYP3A4 inhibitors (such as ketoconazole, erythromycin, cimetidine, grapefruit juice). Enhanced toxicity by: HIV protease inhibitors- It potentiates the hypotensive effects of: nitrates, riociguat. Therefore, its concomitant administration is contraindicated. Potentiation of toxicity with: alpha-blockers. Co-administration of PDE5 inhibitors, including sildenafil, with guanylate cyclase stimulators, such as riociguat, is contraindicated as it can potentially cause symptomatic hypotension. The safety and efficacy of combining sildenafil with other PDE5 inhibitors, other treatments for pulmonary arterial hypertension (PAH) containing sildenafil, or other treatments for erectile dysfunction have not been studied. Therefore, the use of such associations is not recommended.