Increased toxicity w/ sympathomimetic agents (eg, epinephrine) & general anesth (eg, halothane). May result in hypertensive crisis w/ MAOIs (eg, selegiline, moclobemide) & antidepressants (eg, amitriptylline, imipramine). Paracetamol: May increase INR w/ warfarin. May increase susceptibility to the harmful effects of liver w/ medicines for convulsions (eg, phenobarb, phenytoin). May accelerate absorption w/ metoclopramide or domperidone. May reduce absorption w/ cholestyramine. Phenylpropanolamine: May produce additive increase in BP w/ caffeine. Dextromethorphan: CYP450 isoenzyme CYP2D6 inhibitors eg, amiodarone, haloperidol, quinidine, SSRIs & thioridazine. Symptoms of toxicity w/ amiodarone & quinidine. Additive CNS depression w/ alcohol, antihistamines, psychotropics & other CNS depressants.