Your health care provider will instruct you, if necessary, to discontinue drugs that may interfere with the test.
Drugs that can increase 5-HIAA measurements include acetaminophin (Tylenol), acetanilide, phenacetin, glyceryl guaiacolate (found in many cough syrups), methocarbamol, and reserpine.
Drugs that can decrease 5-HIAA measurements include heparin, isoniazid, levodopa, monoamine oxidase inhibitors, methenamine, methyldopa, phenothiazines, and tricyclic antidepressants.
You will be told not to eat certain foods for 3 days before the test. Foods that can interfere with 5-HIAA measurements include plums, pineapples, bananas, eggplant, tomatoes, avocados, and walnuts.