Mmm caffeine. Improve your productivity, but don't overdo it.
Health Effects of Caffeine
Effects on Cognition
Honoré de Balzac is said to have consumed the equivalent of fifty cups of coffee a day at his peak. He did not drink coffee, though—he pulverized coffee beans into a fine dust and ingested the dry powder on an empty stomach. He described the approach as “horrible, rather brutal,” to be tried only by men of “excessive vigor.” He documented the effects of the process in his 1839 essay “Traité des Excitants Modernes” (“Treatise on Modern Stimulants”): “Sparks shoot all the way up to the brain” while “ideas quick-march into motion like battalions of a grand army to its legendary fighting ground, and the battle rages.”
Adenosine acts as an inhibitory neurotransmitter that suppresses activity in the central nervous system. Largely as a consequence of its blockade of adenosine receptors, caffeine also has profound effects on most of the other major neurotransmitters, including dopamine, acetylcholine, serotonin, and, in high doses, on norepinephrine.
As adenosine inhibits dopaminergic neurotransmission, blockade of A2A receptors by caffeine may increase dopaminergic activity and exacerbate psychotic symptoms
...caffeine may reduce the perception of effort by lowering the neuron activation threshold...
Alcohol impaired both inhibitory and activational aspects of behavioral control. Caffeine antagonized alcohol effects on response execution but had no effect on inhibitory control.
"Caffeine tolerance develops very quickly. Tolerance to the sleep disruption effects of caffeine were seen after consumption of 400 mg of caffeine 3 times a day for 7 days, whereas complete tolerance was observed after consumption of 300 mg taken 3 times a day for 18 days."
"It takes about 7-10 days for your receptors to refresh. Gotta go cold turkey. This is how studies are done with caffeine as an ergogenic aid to make sure the effects are not tainted by peoples' built up tolerance."
"I stop caffeine regularly to reset tolerance. I typically feel negative symptoms (headache, inability to focus, fatigue, etc) for 2 days. It usually starts full force at around the 48 hour mark of abstaining. Usually, I have my last coffee Wednesday, negative symptoms kick in Friday, and by Monday I feel completely fine. NSAIDs are your friend for those couple of days. Luckily I have a modafinil prescription, so I just use that to offset fatigue. I have also found that each time I cycle off caffeine, the withdrawal symptoms are less potent than the time before."
"It takes between a week and 12 days to build up a tolerance and dependency on caffeine (even at just one cup a day), and an average of 10 days to work it off."