Monoamine oxidase inhibitors (phenelzine, isocarboxazid), clonidine , selegiline , guanethidine, and ergotamines (ergotamine tartrate, dihydroergotamine mesylate) may increase blood pressure when used at the same time as ephedrine. Methyldopa or reserpine may reduce ephedrine levels in the blood and thereby lessen the effectiveness of ephedrine. Tricyclic antidepressants ( desipramine , amitriptyline , doxepin , and imipramine ) may block the effect of ephedrine. The carbonic anhydrase inhibitors acetazolamide and dichlorphenamide may increase ephedrine blood levels and the risk of side effects from ephedrine. Patients taking any medications should consult with their physician or pharmacist before starting OTC ephedrine.