How long does it take for caffeine to work?

Soon: When taken orally, caffeine takes 15-45 minutes to reach its peak effects in the body although stimulant effects are noticeable at 5-10 minutes. The effects of caffeine are most strongly felt for approximately 2 to 4 hours after onset.

Caffeine Time: Ceffeine is absorbed from your stomach into the bloodstream pretty rapidly. Really it depends how much food is in your stomach at the time the caffeine containing substance is ingested. If your stomach is empty, I would expect to feel the effects in 15-20 minutes. If your stomach is full, it might take 45 minutes to 1 hour but the effect would last longer.