title_body: Is there a "caffeine metabolism curve", understood by general public?
upvoted_answer: Most medications approved by the FDA and used in a medical setting have such statistics.  Caffeine is no exception.  Most drug databases have listed pharmacokinetics for caffeine.  Onset is listed as 15 to 45 minutes with peak concentrations as 30 minutes in adults.  Half life for caffeine varies based on a number of factors.  For adults it is listed as 4 to 5 hours, however, studies suggest it is generally less for smokers.  It is much much longer for infants (52 to 96 hours) but generally by nine months of age, those numbers have dropped to similar levels seen in adults.