Monoamine oxidase inhibitor ( MAOIs ) antidepressants such as isocarboxazid (Marplan), phenelzine (Nardil), tranylcypromine (Parnate), selegiline ( Eldepryl ) and procarbazine ( Matulane ), slow the elimination of amphetamines in the body. This increases the concentration of amphetamines and their effect. This can cause serious elevations in blood pressure (hypertensive crisis) with headaches , other signs of hypertensive crisis, and even fatal reactions. Vyvanse should not be administered until 14 days after MAOIs have been discontinued in order to allow the effects of the MAOIs to dissipate. Amphetamines increase the effect of norepinephrine. Combining both drugs may lead to serious cardiovascular toxicity.