Calcium channel blockers like Amlodipine (Norvasc). Concomitant use of
Amlodipine and
Viagra may cause lowering of blood pressure.
Alpha blockers like doxazosin (Cardura®), prazosin (Minipress®), and terazosin (Hytrin®). Viagra when used in combination with alpha blockers may cause drop in blood pressure, light-headedness, dizziness, or fainting.
Nitrates (nitrogen oxide donors) should not be taken with Viagra. Concomitant use of Viagra and nitrates may cause severe drop in blood pressure.