There's a Scientific Reason You Still Feel Tired After Drinking Coffee

Your genetic makeup could be responsible for you second and third cups.

Are you still tired half an hour after drinking coffee? Do you spend half of your morning stumbling through tasks, waiting for your morning brew to hit you? If your partner is already sailing through the day while you wonder if you accidentally bought the decaf grounds at the grocery store, there could be a genetic difference to blame. Experts have found that there's a scientific reason why it takes longer for some people to feel the effects of caffeine than it does others—and why those effects may disappear more quickly.

A 2014 study in the journal Molecular Psychiatry found six gene variants that seemed to impact the processing of caffeine and therefore coffee consumption of a sample of coffee drinkers. Some of the variants are near genes that are associated with the "rewarding effects of caffeine," per a statement by the Harvard School of Public Health, which was involved in the study, meaning that not everyone gets the same benefits from ingesting it. Others are near genes that are associated with metabolizing caffeine—in other words, processing it to the point where you no longer feel its effects.

Senior couple drinking coffee at cafe
Shutterstock/Jacob Lund

A July 2020 review article in The New England Journal of Medicine notes that "caffeine absorption is nearly complete within 45 minutes after ingestion, with caffeine blood levels peaking after 15 minutes to 2 hours." The liver is responsible for metabolizing the caffeine you eat or drink, and your genetic makeup helps to determine how speedily it can do that.

"The half-life of caffeine in adults is typically 2.5 to 4.5 hours but is subject to large variation from one person to another," the NEJM article states. It also points out that other conditions can affect that half-life, including smoking, which cuts it in half, and pregnancy, which extends it. Some medications, those researchers say, "can slow caffeine clearance and increase its half-life, generally because they are metabolized by the same liver enzymes." So it's important to adjust your caffeine intake if your doctor or pharmacist recommends it.

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All of this is to say that your body's response to caffeine is extremely specific and could be partially inherited. Those whose bodies metabolize caffeine quickly may feel its effects almost immediately and for a relatively short time. Those who are genetically predisposed to metabolize caffeine slowly may not be able to have a sugary Frappuccino in the afternoon without ruining that night's sleep. And these genetic variants probably determine coffee-drinking behavior. So don't assume that the coworker who can survive on one drip coffee to your triple-shot Americano is just more productive. It may be that they are metabolizing caffeine on a much slower schedule than you. And if you're looking for decaffeinated solutions to upping your productivity, here are 25 Ways to Boost Your Energy Level Without Coffee.

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