How does caffeine work?

• A. It blocks adenosine receptors.
• B. It speeds up brain activity by increasing neural firing.
• C. It increases melatonin production.
• D. It enhances GABA inhibition.

Answer: (A)

Caffeine works by blocking adenosine receptors in the brain. Adenosine builds up during wakefulness and acts as a sleep-promoting signal, helping you feel tired. When caffeine binds to the same receptors, it prevents adenosine from exerting its sleepy effect, so you feel more awake and alert. This “take the brake off” effect also lets other wakeful systems (like dopamine and norepinephrine pathways) become more active, contributing to improved focus.

The other statements don’t fit because caffeine does not increase melatonin production, and it does not enhance GABA inhibition. Melatonin helps promote sleep, and caffeine’s action is not to boost its production. GABA is the brain’s main inhibitory system, and caffeine’s effect is to oppose sleepiness by blocking adenosine, not to strengthen GABA’s inhibitory influence.