Like many other medicines, Cialis should not be taken in combination with nitroglycerin/nitrates for heart problems or hypertension (high blood pressure), riociguat, alpha-blockers, grapefruit juice, sildenafil, vardenafil, Adcirca, ritonavir, doxazosin, or antifungal medicines.
Additionally, the following drugs can increase the effects of Cialis by altering the drug's metabolism: ketoconazole, erythromycin, itraconazole, rifampin, and clarithromycin.