Why coffee causes a headache

Coffee can cause headaches in a few different ways, and it usually comes down to how your body reacts to caffeine and changes in it.

One of the most common reasons is caffeine withdrawal or fluctuation. If you usually have coffee (or other caffeine sources) and then skip it or delay it, your brain’s blood vessels can widen slightly, which can trigger a headache. Even just changing your usual timing can do this.

Another reason is too much caffeine at once. High doses can tighten blood vessels, increase stress hormones like adrenaline, and sometimes lead to tension-type headaches or a “wired but uncomfortable” feeling.

There’s also the issue of dehydration. Coffee has a mild diuretic effect for some people, meaning it can make you lose more fluid. If you’re not drinking enough water alongside it, that alone can trigger a headache.

Some people are simply more sensitive to caffeine, where even small amounts can affect sleep, increase muscle tension, or irritate the nervous system enough to cause head pain.

And lastly, it can sometimes be not the coffee itself, but what comes with it—like drinking it on an empty stomach, or combining it with stress, poor sleep, or skipped meals.