Final answer:
The administration of methylergonovine (Methergine) to a heavy smoker can lead to vasoconstriction due to the medication's ergot alkaloid properties and the effects of smoking which also cause blood vessels to constrict.
Step-by-step explanation:
When methylergonovine (Methergine) is administered to a patient that is a heavy smoker, the likely effect is vasoconstriction. This medication is an ergot alkaloid used to prevent or control postpartum hemorrhage by causing the smooth muscle of the uterus to contract. In addition to its uterotonic effects, methylergonovine can also cause vasoconstriction of blood vessels. Smoking, on the other hand, introduces nicotine and other chemicals that can also cause vasoconstriction by stimulating the sympathetic nervous system and releasing catecholamines like norepinephrine, which increases the risk for hypertension and other cardiovascular effects. Therefore, the combined effects of smoking and methylergonovine could lead to increased vasoconstriction.