METHYLPHENIDATE MAY DECREASE THE EFFECTIVENESS OF DRUGS USED TO TREAT HYPERTENSION. METHYLPHENIDATE MAY INHIBIT THE METABOLISM OF COUMARIN ANTICOAGULANTS, ANTICONVULSANTS (E.G., PHENOBARBITAL, PHENYTOIN, PRIMIDONE), AND SOME ANTIDEPRESSANTS (TRICYCLICS AND SELECTIVE SEROTONIN REUPTAKE INHIBITORS). DOWNWARD DOSE ADJUSTMENTS OF THESE DRUGS MAY BE REQUIRED. SERIOUS ADVERSE EVENTS HAVE BEEN REPORTED IN CONCOMITANT USE WITH CLONIDINE.