**Core Concept**
Cocaine is a potent stimulant that affects the cardiovascular system by altering the normal function of blood vessels. It primarily acts as a vasoconstrictor, causing blood vessels to constrict or narrow. This effect is due to its action on the sympathetic nervous system, specifically through the release of norepinephrine.

**Why the Correct Answer is Right**
Cocaine blocks the reuptake of norepinephrine, a neurotransmitter that stimulates the alpha-1 adrenergic receptors on the smooth muscle cells of blood vessels. Stimulation of these receptors leads to vasoconstriction, which increases peripheral resistance and blood pressure. This is a critical mechanism by which cocaine exerts its cardiovascular effects, particularly in individuals with pre-existing hypertension or cardiovascular disease.

**Why Each Wrong Option is Incorrect**
**Option A:** Cocaine has a vasodilatory effect, which is incorrect as it primarily causes vasoconstriction.
**Option B:** Cocaine does not primarily act on the parasympathetic nervous system, which is responsible for promoting relaxation and reducing heart rate.
**Option C:** Cocaine does not cause vasodilation, which would lead to a decrease in blood pressure.

**Clinical Pearl / High-Yield Fact**
Cocaine-induced vasoconstriction can lead to acute coronary syndromes, including myocardial infarction, particularly in young individuals with no prior cardiovascular risk factors.

**Correct Answer:** C.