What role does caffeine play in the life of a plant? According to “the naked scientists”, it plays a part in their defence mechanisms.
So it seems that caffeinated plants are lucky to have this compound as part of their natural defences, but it doesn’t deter all attackers. For instance, caffeine doesn’t poison humans in the doses that we typically ingest (even a Monday morning dose), but it does cause addiction. It works by stopping the enzyme phosphodiesterase from breaking down a signalling substance called cyclic AMP (cAMP for short) and its close relatives. One of the actions of the stress hormone adrenaline is to increase the levels of cAMP in cells, so by preventing cells from breaking down cAMP, caffeine potentiates the action of adrenaline, and gives us a buzz. In even higher doses, and with prolonged use, it can trigger anxiety, muscle tremors, palpitations and fast heart rates, and profound withdrawal effects
including headaches, inability to think clearly, and bad moods whenever you mistakenly switch to decaff !