Which of the following is a symptom of caffeine intoxication?

Restlessness is a well-documented symptom of caffeine intoxication. Caffeine is a central nervous system stimulant, and when consumed in excessive amounts, it can lead to heightened levels of arousal and agitation. Individuals experiencing caffeine intoxication often report feeling jittery or restless, which results from the stimulant effects of caffeine on the brain. This response is due to caffeine's ability to block adenosine receptors, leading to increased neuronal firing and the release of neurotransmitters that enhance alertness and anxiety.

In contrast, weight gain and loss of appetite are typically not associated with caffeine intoxication; in fact, caffeine can sometimes suppress appetite. Increased drowsiness is also contrary to the expected effects of caffeine, as it generally promotes wakefulness and alertness, rather than inducing sleepiness.