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The time it takes for the body to eliminate one half of a caffeine dose is normally between 3 to 12 hours. It is called the half-life of caffeine. Several factors can shorten or lengthen the half life of caffeine. Smoking, medications and diseases are some factors.
Advertisement. It only takes 45 minutes for 99% of the caffeine to be absorbed through these membranes. In humans the half-life for caffeine is anywhere from 4 to 6 hours on average, which explains why the average energy drink or coffeeâs effect lasts about 4 to 6 hours.n humans the half-life for caffeine is anywhere from 4 to 6 hours on average, which explains why the average energy drink or coffeeâs effect lasts about 4 to 6 hours.