Have you ever wondered why we crave caffeine or nicotine when we consume them regularly? Or why, after a while, all we’re doing is satisfying the craving? And why we don’t feel so good without our drug of choice after we’ve adapted to it? It’s all about what happens when these substances attach to receptors on the surfaces of cells in our bodies…
Many drugs work by attaching to a receptor on the surface of a cell—we can think of receptors as tiny “locks” throughout our bodies, each one with its specific shape, waiting for the substance (its “key”) to come along, attach, and turn the receptor on. This creates an action inside the cell, like caffeine giving us energy, or nicotine relaxing us. When the effect is pleasant, or helps us feel better, sometimes we keep consuming these “keys”, like caffeine, nicotine, alcohol or even narcotics, trying to keep the effect going.
However, your body always tries to keep things on an even keel. We call this “homeostasis”. So, if you keep lots of your drug of choice in your system, eventually your cells make more receptors for the drug. This results in you just feeling your ordinary self when the substance is in your system. This is known as "developing tolerance" to the drug.
Of course, it's a bit more complicated than this, with other substances often attaching to the same receptor, creating competition and sometimes providing different actions, but you get the idea. It depends on which key gets into the lock and whether it turns it on.
But if you don’t consume a favourite drug you use daily, after a little while you’ll have lots of empty receptors looking for the “keys” they’re used to having. This can cause you to feel not-so-great. With caffeine, you may have a headache and feel sluggish; with nicotine you may become irritable, feel anxious, or have insomnia.
You start to crave the drug because you know it will make you feel better but, really, once you've developed tolerance to the drug, all it will do is make you feel like your regular self. That's why people will sometimes gradually increase the amount of drug they use, as they try to get the same drug effect that they used to experience.
This lock-and-key concept applies to many substances, from hormones to some medications you take. Even drugs like Tylenol and Advil can eventually cause headaches if taken daily, then suddenly stopped. We call this “medication induced headache” and it happens because your body has adapted to having the medication there all the time.
Without the substance around for a period of time, cells gradually return to making fewer receptors again and the cravings will stop. Some receptors, like those for opiates and nicotine, take longer to return to normal numbers, making these drugs harder to quit. Caffeine receptors seem to return to normal amounts in 3 or 4 days when you quit coffee, and cravings and withdrawal are much less of a problem if you taper your coffee intake gradually.
This week I came across the cutest explanation of how all this works by David B. Clear (a scientist/blogger/cartoonist who lives an idyllic life on an island in the Mediterranean). He uses caffeine as an example. Since I’ve had an extra-busy week, I’m just going to share it with you. He’s also much funnier than I am and even uses cartoons to explain how caffeine works and why we crave it so much. I don’t know about you, but making coffee is the first thing I do when my feet hit the floor in the morning! I’ve always thought it was the taste I was craving… but I very likely have lots of extra caffeine receptors waving around in my brain!
Anyway, here’s the link… hope you enjoy this fun science-y explanation of how caffeine works and why we crave it!
