Caffeine, A partial agonist ..Same as Kratom, Mitragyna Speciosa
The stimulant effect of coffee comes largely from the way it acts on the adenosine receptors in the neural membrane. Adenosine is a central nervous system neuromodulator that has specific receptors. When adenosine binds to its receptors, neural activity slows down, and you feel sleepy. Adenosine thus facilitates sleep and dilates the blood vessels, probably to ensure good oxygenation during sleep.
Caffeine acts as an adenosine-receptor antagonist. This means that it binds to these same receptors, but without reducing neural activity. Fewer receptors are thus available to the natural “braking” action of adenosine, and neural activity therefore speeds up (see animation).
The activation of numerous neural circuits by caffeine also causes the pituitary gland to secrete hormones that in turn cause the adrenal glands to produce more adrenalin. Adrenalin is the “fight or flight” hormone, so it increases your attention level and gives your entire system an extra burst of energy. This is exactly the effect that many coffee drinkers are looking for.
In general, you get some stimulating effect from every cup of coffee you drink, and any tolerance you build up is minimal. On the other hand, caffeine can create a physical dependency. The symptoms of withdrawal from caffeine begin within one or two days after you stop consuming it. They consist mainly of headaches, nausea and sleepiness and affect about one out of every two individuals.
Lastly, like most drugs, caffeine increases the production of dopamine in the brain’s pleasure circuits, thus helping to maintain the dependency on this drug, which is consumed daily by 90% of all adults in the U.S.
The definition of a partial agonist ~
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