Predisposition to arrhythmias w/ other β-sympathomimetics eg, amphetamines. Marked hypotension w/ Ca antagonists especially dihydropyridine class; unpredictable hypotension w/ other vasodilators eg, ACE inhibitors (eg, captopril, enalapril, lisinopril) or α
1-adrenoceptor antagonists (eg, prazosin). Enhanced anesth effects w/ MAOIs. Risk of hepatotoxicity w/ INH. Potentiated resp depressant effects w/ opioid analgesics. β-blockers.