Stimulant in Coffee, Tea; Avoid It Before Bed
Puzzle 2 of Bedtime Piece of Cake Pack
Question is: Stimulant in Coffee, Tea; Avoid It Before Bed
and the answer is: CAFFEINE
Word Meaning:
CAFFEINE — An alkaloid, C₈H₁₀N₄O₂, found naturally in tea and coffee plants, which acts as a mild stimulant on the central nervous system.
Definitions from Wiktionary.