stimulant

Caffeine is a natural stimulant that helps many people stay awake during the day.

(Chinese) 咖啡因是一种天然兴奋剂，能帮助许多人在白天保持清醒。

The athlete was disqualified after testing positive for a banned stimulant in his blood.

(Chinese) 由于血液中违禁兴奋剂检测呈阳性，该运动员被取消了参赛资格。