system
Given the following post, respond as if you're commenting on Reddit:
human
Does your body build up a resistance to caffeine?

And if so can this be reversed by stopping the intake of caffeine for a certain amount of time or is it permanent?
gpt
Yes, it does. Caffeine works by blocking the action of *adenosine*, which is an inhibitory neurotransmitter (i.e. nerves release it into synapses to reduce the likelihood that nearby nerves will fire).  By blocking adenosine, caffeine stimulates activity.

But, like pretty much all systems in the body, the adenosine system is subject to long-term feedback and over the course of days to weeks you will develop more adenosine receptor sites, so that more caffeine is required to block them all.  That is the primary pharmacological tolerance mechanism.

Fortunately, the feedback works both ways so if you stop ingesting caffeine your adenosine system will revert to normal on the same general time scale.