The Deal

• $12 for four vouchers, each good for $5 worth of coffee, baked goods, and comic books ($20 total value)

Caffeine: An Energetic Impostor

An obvious part of the appeal of coffee and tea is their ability to widen your eyes and put a spring in your step. Learn how they do it with Groupon’s quick look at the neurochemistry of caffeine.

Behind caffeine’s seemingly magical stimulating effect is some simple neurological sleight of hand. To understand it, it’s helpful to first take a microscopic look at what makes us tired in the first place. Every time a neuron fires, it produces a neurotransmitter called adenosine. Receptors in the nervous system gauge the levels of adenosine in the brain, running through the spinal cord, and emanating from the top of the head. As those levels rise continually throughout the day, the brain is programmed to start winding down.

Therefore, as adenosine builds, one’s sense of alertness fades—unless caffeine enters the equation. Caffeine molecules happen to be shaped just like adenosine, and the receptors in charge of monitoring the neurotransmitter’s presence cannot distinguish one from the other. Caffeine binds to the receptors just as adenosine would and simply blocks them, preventing them from detecting actual adenosine and transmitting the associated message of fatigue to the body. In so doing, caffeine forestalls the body’s sense of tiredness until the dose wears off and the brain can detect real adenosine again, typically five or six hours later.