Overview
Adenosine is one of the four components of RNA and forms adenosine triphosphate (ATP) as the main source of energy in human cells. It directly interacts with dopamine pathways and reward circuits in our brains, which can be disrupted through chronic substance use. Adenosine can function as a kind of “brake” for excessive dopamine signaling, so if it depletes in the course of a dopamine surge from a substance or process, its receptors become desensitized as well. Once dopamine flows without breaks from adenosine, the brain reduces overall dopamine receptors to protect itself, which then lowers the brain’s baseline dopamine production. This leads to dampened rewards experienced from daily life while fueling cravings for more of the addictive substance or process.
Caffeine directly blocks adenosine receptors, so the brain’s natural dopamine prduction flows more freely. The brain responds by building more adenosine receptors, which is how tolerance for caffeine builds over time and fatigue headaches set in when suddenly stopping. On the other hand, alcohol floods the brain with adenosine by blocking a protein, called the ENT1 transporter, that would remove extra adenosine. This explains how caffeine and alcohol can both be addictive to the brain and interfere with dopamine pathways while also producing the exact opposite effects in terms of alertness and sedation.