One cup of strong coffee, or tea, per day does seem to raise the speed and accuracy of your thinking, but more than that one rapidly produces fatigue and then addictive tendency to drink more caffeine to try and combat fatigue.
Caffeinated drinks like Coke and Red Bull often exacerbate your thinking problems by producing ‘insulin swings’ that make difficult to concentrate.
Caffeine can quicken your reaction time and prolong your vigilance during demanding tasks and it contains protective antioxidants but dark chocolate gives more protection and safer ‘buzz’.
Once you started to drink coffee, there is a need to keep doubling your intake to have the same effect and eventually a plateau is reached. The caffeine acts as a diuretic; you keep urinating, causing dehydration. This produce lethargy and reduces your cognitive performance. Dehydration has a major adverse effect on mental activity. Tap water, hot water or herbal tea, all produce greater benefits to thinking.
The first buzz from the first cup is quickly negated by subsequent fatigue.