Why does espresso make me tired? It’s all I drink. Rarely regular coffee. I live in Rome. Italians say it aids digestion which is why you can have it after dinner and fall right asleep. But it doesn’t wake me up ever. I ran a marathon with zero caffeine. I often go out for a run without any coffee. Then I have one afterwards and feel relaxed. Does caffeine affect some people this way?

Your experience with espresso possibly making you feel relaxed rather than energized is not uncommon. The effect of caffeine can vary significantly among individuals, mainly due to genetic differences that affect how caffeine is metabolized in the body. Some people have a genetic variant that leads to slower metabolism of caffeine, making them less sensitive to its stimulating effects, allowing them to consume coffee and feel relaxed or sleepy instead of alert 1 2.

Caffeine works by blocking adenosine receptors, thus preventing you from feeling sleepy. However, it doesn't remove adenosine from your system; it just temporarily prevents it from binding to receptors. Once the caffeine wears off, there's a buildup of adenosine that can lead to a feelings of tiredness or a "caffeine crash" 2 3.

Additionally, environmental and lifestyle factors also influence caffeine's effects. Regular consumption can increase your tolerance, reducing its stimulating effects 4. If you often feel relaxed or tired after drinking espresso, it might be due to these genetic and tolerance factors, along with the fact that caffeine's primary effect is more pronounced on those who are more sensitive to it.

In your case, running without any caffeine might align with your body's natural energy rhythms, and consuming coffee afterward as a part of routine or social ritual rather than for an energy boost might be why it has a calming effect.