I’ll be honest: I had no idea people really drank coffee to perk them up. I thought that was just a fun American TV thing and we were all really in it for the taste.
This is because, in my experience, drinking caffeine actually makes me sleepier.
Turns out I’m in the minority, but not alone. Smoking, oral contraceptives, and caffeine “tolerance” among regular drinkers may cause some of us to feel ready to rest after a cup of java, News Medical Life Sciences says.
Gastrointestinal surgeon, author and lecturer Dr Karan Rajan recently shared a TikTok video in which he listed another reason for post-caffeine fatigue ― it’s all down to our liver, he says.
How does my liver affect how I feel after caffeine?
“If caffeine makes you feel tired, it might be because of a software glitch in your caffeine gene,“ the doctor began his video.
He explained that people tend to be either fast or slow metabolisers of caffeine ― which one we get depends on which type of liver enzyme, known as CYP1A2, we have.
The enzyme affects how sensitive your body is to caffeine. “Depending on your metabolism, it could take between two to eight hours to remove half of the caffeine” you’ve drunk from your system, Dr Rajan continues.
That matters because caffeine blocks our adenosine receptors, a part of the body which tells us we’re sleepy.
If you metabolise coffee faster, you’ll unblock those receptors sooner – and, well, you’ll feel tired.
A 2023 paper found that those with the “slower” version of the liver enzyme were more likely to develop kidney conditions than those who barely notice caffeine’s effects.
Dr Rajan also agreed with the “caffeine tolerance” theory, stating that when you get used to drinking coffee or other caffeine-containing drinks, your body responds by simply making more adenosine receptors (oh, good).
Is feeling tired after drinking coffee something to worry about?
The Sleep Foundation says the effect could, potentially, lead to a vicious (sleep) cycle ― if you’re not perked up by coffee, you might drink more of it in an attempt to stay alert.
But that may in turn cause you to stay up later, which will lead you to feel more tired the following morning, which may inspire you to drink more coffee, which... you get the picture.
Some people claim that feeling tired after drinking coffee is a sign of ADHD.
Though this is commonly self-reported among those with the condition, ADHD app Inflow says there is no concrete proof that the link exists or works in that way.