5 hours.
As long as caffeine is in your blood, it's effects will also manifest. 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. What’s extraordinary is that caffeine when injected in the body doesn’t accumulate in one place but is spread through the body. It also varies from man to woman. Scientifically, caffeine resides longer in women’s system than that of men. The average half-life of caffeine in healthy humans persists for 4.9 hours. In men, typically residing between 5 to 9 hours, after the consumption of caffeine. How Long Does Caffeine Stay in the Body? In most cases, caffeine has a half-life of about 5 hours (meaning 5 hours is needed to eliminate half the coffee amount). However, it might take longer – for instance, a pregnant woman might have caffeine in her system up to 20 hours after she ingests it. Onset and Duration. It takes approximately 15 to 45 minutes for caffeine to reach its peak levels in your bloodstream. Caffeine has a half-life of approximately five to six hours, meaning that it takes this long for its concentration in your bloodstream to reduce by half. It shows just how long every caffeinated drink (and some food) stays in your system over the course of the day, assuming an 8oz serving size. The reason that last coffee didn't do it for you? Just one hour post-digestion, the amount of caffeine in an 8oz serving of coffee goes from 140mg to 123.9mg.
http://neutral-izer.blogspot.com/2007/09/how-long-does-caffeine-stay-in-your.html http://www.actabit.com/long-coffee-caffeine-stay-system/ http://www.med-health.net/How-Long-Does-Caffeine-Last.html http://www.livestrong.com/article/272782-how-long-does-coffee-caffeine-stay-in-your-system/ https://www.thrillist.com/drink/nation/how-long-every-caffeinated-beverage-stays-in-your-system-soda-coffee
how long caffeine stays in your system