Caffeine has various effects on your body.
A natural stimulant found in coffee, tea, chocolate, soft drinks, and more, caffeine is the most commonly consumed psychoactive substance, according to studies. It’s beloved for its ability to boost mood, increase metabolism, and enhance athletic performance as well as boost concentration, alertness, and motivation.
In particular, it affects the brain. After you consume caffeine, it’s dissolved into the bloodstream and quickly reaches the brain.
Next, caffeine fits into and blocks adenosine receptors in the brain, thus preventing the molecule adenosine from making you tired. Not only that, but this process causes blocked receptors in the brain to release other natural stimulants and enhance their effects. In return, you feel alert and stimulated.
When you drink caffeine on a regular basis for a prolonged amount of time, it can cause the chemistry of your brain to change. For example, the brain may compensate for those aforementioned blocked adenosine receptors but make even more receptors. With this, a greater amount of receptors, you'll have to drink even more caffeine to get the same stimulating effects as before.
And, if you quit caffeine cold turkey, you would have an excess of unblocked receptors for adenosine to bind to, ultimately leading to tiredness.
Obviously, that makes you want it more and crave that good feeling. You end up drinking more and more to chase that feeling of alertness.
Some believe it’s more of dependence than an addiction, though. Nothing we can't google further :)