Why cannot aspirin be taken with metoprolol?

High doses of salicylates (aspirin) may blunt the antihypertensive effects of beta-blockers. The proposed mechanism is inhibition of prostaglandin synthesis. Low-dose aspirin does not appear to affect blood pressure. In addition, beta-blockers may exert an antiplatelet effect, which may be additive with the effects of some salicylates. Metoprolol may also increase aspirin absorption and/or plasma concentrations of salicylates; however, the clinical significance of this effect is unknown. Data have been conflicting. Until more information is available, patients who require concomitant therapy should be monitored for altered antihypertensive response whenever a salicylate is introduced or discontinued, or when its dosage is modified. Regardless, the problem is rather minor.