The effects of caffeine start within 10 minutes after it is consumed, according to ScienceDaily. However, caffeine requires 45 minutes to reach its maximum concentration in the blood.
Caffeine is an immediate stimulant as its effects can be felt within 10 minutes of consumption. According to ScienceDaily, this was reported in a study conducted by the researchers at the University of Barcelona in Spain. However, this research study also reported that caffeine attains its maximum concentration in the blood 45 minutes after consumption.
In previous studies, it was reported that people experienced increased alertness 30 to 45 minutes after consuming beverages containing caffeine. Nearly 90 percent of adults consume caffeine daily in North America, according to Villanova University.