Which stimulant can increase alertness and wakefulness but also cause anxiety, restlessness, and insomnia in high doses?

• A. Nicotine
• B. Caffeine
• C. Amphetamine
• D. Methylphenidate

Answer: (B)

Stimulants boost brain arousal to increase alertness and wakefulness, but at higher doses that arousal can become overwhelming, leading to anxiety, restlessness, and trouble sleeping. Caffeine works by blocking adenosine receptors, which normally promote sleepiness; with more caffeine, wakefulness is amplified and sleep pressure drops, making you feel more awake even as you’re anxious and have difficulty falling or staying asleep. This dose-related pattern—enhanced alertness paired with anxiety and insomnia at higher amounts—is closely linked to caffeine, the widely used stimulant. While other stimulants can also cause these effects at high doses, caffeine’s common use and clear dose-response make it the best fit for this scenario.