The calculus of caffeine consumption rests on a few basic ideas:
Caffeine has a number of effects on the body, but the one that is relevant here is that it blocks adenosine receptors in the brain (by tricking your brain into thinking it is adenosine.) A decrease in the activity of adenosine (which is a sleep chemical) increases neuron firing rate and increases focus and concentration.Caffeine tolerance builds up rather quickly (2-3 weeks) and further, is near-total. That means that if you drink coffee regularly, pretty soon you start producing more adenosine in respose; thus you need your caffeine dose just to get up to your normal level of brain activity, and you’re dopey if you don’t take it. Another way to think about it is that the time-average of adenosine level (and hence, attention level) tends to stay more-or-less constant, both short term and long term.
Let us examine the way that most people take caffeine — when they feel sleepy (I will call this antagonistic consumption.) This changes the attention level from the green line to the blue line (i.e, it smooths out the fluctuations.) This works great for many people (say, someone that has a data entry job), because maximum productivity is limited by external constraints. Other jobs where antagonistic consumption is essential include assembly line worker and truck driver, where mistakes can be disastrous but there is little to be gained from peak concentration.But other jobs, often characterized by a low level of repetition, have a markedly different attention-productivity curve. Academic research, for instance, involves generating ideas that no one has come up with before. Clearly, an idea that advances the state of the art is unlikely to occur except when attention level peaks. If you spend your entire day doing nothing, but all that doing nothing somehow enables you to reach a point where you understand your research problem well enough that you get insights that no one ever did before, then that’s good research. Writers are another example: it is common to sit around for days or weeks waiting for inspiration to hit (“writer’s block”).
What is common to these tasks is that progress happens in spurts, due to the fact that they involve frequent cognitive bottlenecks. A cognitive bottleneck can only be overcome when attention level exceeds a task dependent, typically very high threshold. Clearly, then, antagonistic caffeine consumption results in worse-than-normal productivity, because it flattens the attention level curve and decreases the fraction of time spent at peak attention level. Instead, reinforcing consumption helps maximize productivity (the red line). According to this strategy, the best time to drink coffee is when you are already very alert.