Refers to a substance that stimulates the body or mind, such as caffeine or a drug. Can also mean an irritant that provokes a reaction.
The caffeine in coffee is a mild stimulant.
This chemical can be an irritant to the skin.
Figurative use: something that motivates or spurs a person to action, such as an incentive or a challenging event.
His success became a great motivator for me.
Competition can sometimes be a good spur.
興奮剤 is a stimulant that causes excitement or arousal, often used in medical or pharmacological contexts, while 刺激剤 is broader and includes irritants and figurative motivators.
Compound of 刺激 (しげき, 'stimulus') + 剤 (ざい, 'agent' or 'drug'). The kanji 刺戟 is a variant spelling where 戟 is an older form of 激, now rare.