• Caffeine is a stimulatory anti-sleep compound extracted from coffee beans. Habitual caffeine use leads to tolerance, which dulls several of caffeine’s effects.

Caffeine comes from coffee beans, but it can also be synthesized in a laboratory. It has the same structure whether it’s in coffee, energy drinks, tea or pills.

Caffeine is a powerful stimulant, and it can be used to improve physical strength and endurance. It is classified as a nootropic because it sensitizes neurons and provides mental stimulation.

Habitual caffeine use is also associated with a reduced risk of Alzheimer's, cirrhosis, and liver cancer.

Caffeine’s main mechanism concerns antagonizing adenosine receptors. Adenosine causes sedation and relaxation when it acts upon its receptors, located in the brain. Caffeine prevents this action and causes alertness and wakefulness. This inhibition of adenosine can influence the dopamine, serotonin, acetylcholine, and adrenaline systems.

Habitual caffeine use leads to tolerance. This means the effects of caffeine will be diminished, often to the point where the only benefit a user experiences is caffeine’s anti-sleep effect. This is an ‘insurmountable’ tolerance, which means more caffeine will not overcome it. A month-long break from caffeine will reduce tolerance.