Final answer:
Caffeine is a CNS stimulant that promotes wakefulness and blocks the action of adenosine. It is not a CNS depressant, does not cause cerebral vasoconstriction, and is not a gastric irritant. Caffeine does not reduce plasma glucose levels and is only a mild diuretic.
Step-by-step explanation:
Caffeine is a CNS stimulant that blocks the action of adenosine on its receptors, preventing drowsiness and promoting wakefulness. It is not a CNS depressant.
It does not cause cerebral vasoconstriction. In fact, it is thought to have the opposite effect by potentially dilating blood vessels in the brain.
Caffeine does not reduce the acidity of gastric fluid secretion and can actually increase gastric acid secretion, making it a gastric irritant.
Caffeine does not reduce plasma glucose levels. It can increase blood glucose levels by stimulating the release of catecholamines and inhibiting insulin secretion.
While caffeine has mild diuretic effects, it is not considered a potent diuretic.