Levels of circulating caffeine peak approximately thirty minutes after oral administration. What is problematic, though, is the persistence of caffeine in your system. In pharmacology, we use the term “half-life” when discussing a drug’s efficacy. This simply refers to the length of time it takes for the body to remove 50 percent of a drug’s concentration. Caffeine has an average half-life of five to seven hours. Let’s say that you have a cup of coffee after your evening dinner, around 7:30 p.m. This means that by 1:30 a.m., 50 percent of that caffeine may still be active and circulating
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