Why your morning coffee might be making you sleepy

Some people experience spikes in blood pressure, while others get trembling hands. However, after your nth cup of strong coffee, you may notice no changes and find your eyelids growing heavier despite consuming a hefty caffeine dose. Why does this happen?

For many, their morning ritual cannot be done without a cup of coffee. The dark brew is known for its stimulating and energising properties, thanks to caffeine, which improves concentration and aids focus on daily tasks such as work or study. However, coffee sometimes causes the opposite effect and makes you sleepy instead of the expected stimulation. So, can coffee make you sleepy? Why does coffee often make you want to sleep?

Some people do not feel the stimulating effect of coffee because their bodies are resistant to it. This resistance results from regular coffee consumption and a high tolerance to caffeine. Ahmed El-Sohemy, a professor of nutritional sciences at the University of Toronto, mentioned in an interview with "The Washington Post" that nearly half of all people metabolise caffeine quickly, another 40 percent metabolise caffeine slowly, and the remaining 10 percent have a very slow metabolism – meaning they react strongly to caffeine doses.

Many people feel sleepy after drinking coffee, and this usually affects those who metabolise caffeine faster and consume more coffee. Why is this? Caffeine blocks adenosine receptors, which are responsible for causing drowsiness, but it does not inhibit the production of adenosine. As a result, when the effect of caffeine wears off and the adenosine receptors are unblocked, the fatigue returns with greater intensity.

The more caffeine you consume, the longer adenosine is blocked, which delays the feeling of drowsiness. However, regular consumption of large amounts of coffee causes the body to adapt by producing more adenosine receptors. This means that you need increasing amounts of caffeine to achieve the same effect of blocking the receptors responsible for drowsiness, which increases the body’s tolerance to caffeine.

Another factor affecting your response to coffee is your tolerance to sugar. Sugar is absorbed by the body more quickly than caffeine. When you drink coffee with milk and sugar, it causes a rapid increase in insulin levels. For people with sugar metabolism disorders, this results in only temporary stimulation while drinking, followed by marked fatigue, drowsiness, and lack of energy. Headaches can also be a normal bodily reaction in such situations.

If you feel sleepy after drinking coffee but don't want to give it up, it’s worth changing your habits. It’s important not to exceed the recommended daily dose. It’s also better to avoid additives such as sugar, milk, or flavoured syrups because coffee without these additives will work more effectively. If you still do not feel well after drinking coffee, an alternative could be green tea or the increasingly popular matcha, which are also stimulating and energising.