See also How to Use section.

Drug interactions may change how your medications work or increase your risk for serious side effects. This document does not contain all possible drug interactions. Keep a list of all the products you use (including prescription/nonprescription drugs and herbal products) and share it with your doctor and pharmacist. Do not start, stop, or change the dosage of any medicines without your doctor's approval.

Check all prescription and nonprescription medicine labels carefully since vitamins/dietary supplements may also contain niacin or niacinamide (nicotinamide). These may increase your risk of side effects if taken together. Ask your doctor or pharmacist for more details.

This medication may interfere with certain lab tests (such as urine or blood catecholamines, copper-based urine glucose tests), possibly causing false test results. Make sure lab personnel and all your doctors know you use this drug.