Caffeine is the world's most commonly consumed psychoactive substance. Caffeine is mainly found in coffee, tea and chocolate, but it is also added to certain beverages or foods. [1]

Caffeine is the most commonly consumed psychoactive substance worldwide. Caffeine is mainly found in coffee, tea and chocolate, but is also added to certain drinks or foods. [1]

Physiologically, caffeine reduces drowsiness and promotes performance by acting as an adenosine antagonist and inhibiting sleep-promoting neurochemicals. [2]

However, caffeine can also negatively impact sleep quality. In a 2016 review, researchers took another look at the effects of coffee and found that caffeine increases the time it takes to fall asleep and decreases sleep duration and efficiency. [1]

The effect can be very different for each individual. 

Twin analyses have shown that sleep is disturbed by caffeine, especially in people with a certain variation in the adenosine A2A receptor gene. [3]

The time at which caffeine is consumed also plays a crucial role. Scientists confirm that evening coffee consumption can shift circadian rhythms by interfering with melatonin production. [4] 

But habitual drinkers are less bothered by caffeine. They are less likely to report sleep impairment than people who only consume caffeine occasionally. [5]