Caffeine stays in your system for longer than you may think. The half life of caffeine—i.e., the amount of time it takes for the body to process just half—is usually around five hours, but can vary from one to as much as nine hours, says Meredith Broderick, M.D., neurologist and sleep specialist.
Most caffeine (i.e., the instant-release stuff) is fully absorbed 45 minutes after being ingested, but doesn’t leave the body for a while. According to Kogan, full metabolism of caffeine can take up to 10 hours.
The less common, extended varieties of caffeine intentionally prolong the release of caffeine over time, sustaining its levels in the blood and its benefits, while buffering against dreaded “crash” phenomena. This also means you would want to take it earlier in the day, so the energizing effects don’t bleed into your nighttime ritual.
As you can imagine, not everyone metabolizes caffeine the same, which results in discrepancies between individual’s experiences. Caffeine sensitivity depends on age, sex, genetic makeup, and environmental factors (e.g., whether the person smokes or is pregnant), shares Broderick.
As mentioned, your genes have a profound effect on your sensitivity to caffeine, too. “Variations in the CYP1A2 and AHR genes have been shown to impact how quickly the body metabolizes caffeine. Research has also shown that people with a variation in their ADORA2A gene experience stronger caffeine effects and for longer periods of time,” Kogan notes.
A classic eight-ounce cup of coffee contains about 96 milligrams of caffeine. But honestly, most of us are more likely to reach for 16 ounces of brewed coffee or cold brew, which have double the caffeine content. A 2018 review states that the average American adult consumes about 200 milligrams of caffeine every day, confirming this hypothesis.