Oral absorption and concentration-effect relationship of tyramine with and without cimoxatone, a type-A specific inhibitor of monoamine oxidase. The mechanism of increased sensitivity to oral tyramine in patients taking monoamine oxidase inhibitors was investigated by measurement of plasma norepinephrine and tyramine with a reversible, monoamine oxidase form A selective inhibitor, cimoxatone . In the first open study, the pressor activity of 80 mg oral tyramine after cimoxatone was of the order of that of 800 mg without the drug. In a second double-blind study, the equivalent tyramine dose was between 400 and 800 mg. Absorption of unmetabolized tyramine increased in the presence of cimoxatone. Peak plasma concentration of tyramine after an 80-mg dose was approximately three times that of placebo