A neuroscientist from Uniformed Services University of the Health Sciences suggests that the most effective time for drinking coffee was between 9.30am and 11.30am.
Steven Miller said that drinking coffee between 8am and 9am would be counterproductive as the levels of stress hormone cortisol in people would be high and caffeine interacts with the hormone. He said that cortisol levels would be high in people as soon as they get up and starts to fall about an hour afterwards.
Cortisol level is also at its peak at lunchtime and between 5.30pm and 6.30pm. Drinking coffee when cortisol level is low would help boost the hormone production when the levels start to drop and they do not become resistant to its benefits.