“I’m going to head to Tim Horton’s for a coffee.”
“Sure, no problem.”
You walk to Tim’s and you begin to realize you’re hungry. It’s 11:45 AM and lunch is only fifteen minutes away. You’ve brought your lunch to work today as well so you should be good.
Just a coffee, you say to yourself.
“Hi, welcome to Tim Horton’s! May I take your order?”
“Hi, yes I’ll have a large coffee with milk, a vanilla dip doughnut, and a pack of those doughnut sticks you have.”
What is it that makes fried, sugared dough addictive? Or deep-fried potatoes? Or sour patch kids? Or anything, for that matter?
In our brains, there exists something called the nucleus accumbens. This part of the brain is known as the reward centre. What does this mean? Every time you do something that feels good, this centre “pings,” and makes you feel good. Why does this part of the brain exist? Well, it’s actually essential to our survival! Things like eating, drinking water, and having sex, are vital biological functions for our species. Without them, we would not survive. Very few of us, however, are thinking about, “I need to survive and propagate my genes,” as we eat and have sex. No, most of us do these things because they feel good. That’s where the nucleus accumbens comes in. It pings and rewards us with a shot of dopamine, the brain’s “happiness chemical,” when you do something that’s good, biologically. It’s a built-in incentive system to ensure we are doing, and feel good about doing, those functions essential for species survival.
This system, however, is imperfect, and it is prone to being hijacked. The nucleus accumbens is where many substances of abuse act, including cocaine, crystal meth, and any number of drugs. This is why many people with drug addiction become very skinny, and can waste away. The drugs hijack the system, and reward you more than food. Drugs steadily train the brain that the best rewards come from the drugs, and not food or water or sex. A great example of how strong the craving for drugs can be is a study that examined rats, who had electrodes placed in their brain at the site of the nucleus accumbens. The rats were given the ability to hit a button in their cages, which would activate the electrode, stimulate the nucleus, and cause a reward. The rats eventually choose to die while hitting the button, and totally neglect vital functions such as eating and drinking.
But what is it that makes a substance addictive? Sugary foods can be addictive and cause cravings, for example, while carrots almost certainly do not. Cocaine and crystal meth are extraordinarily addictive drugs, while ritaline and vyvanse, medications for ADHD which act similarly, are not. What is responsible for this difference?
We think we know!
The nucleus accumbens appears to be sensitive the the size of a potential reward. Finding a penny on the ground, for example, makes us feel a lot less better than finding a one hundred dollar bill. Biologically, this discrimination has allowed the brain to prioritize eating high caloric foods, over low caloric foods, although both may taste good. (This function would have evolved prior to the food-availability we experience today in the Western world – the drive to eat higher calorie foods is a clear disadvantage to many of us nowadays.) The same principle applies today, which is why sugary, fatty foods are so addictive. The sugar and the fat, the nutrients essential to life which are activating the nucleus accumbens in the first place, are higher in doughnuts than they are broccoli, and therefore we crave doughnuts. This is actually a great example of how the advantage of a particular behaviour, and whether it is a mental illness, depends entirely on context. A drive to eat high caloric foods would have previously been evolutionary essential – now it causes heart disease.
So what’s the deal with drugs?
Well, the same principle applies. The strength of a stimulus is directly proportional to how addictive the substance is. So what affects the strength? Food that are higher in sugar and fat cause a higher level of nucleus stimulation, therefore we crave food that are slowly killing us. This is also true for drugs of abuse; crystal meth is several orders of magnitude stronger than cocaine, and meth is a hell of a lot more addictive. But there’s more! The speed of the stimulus also matters!
When a sugar/fat/drug reward is given to us suddenly, the nucleus reacts more strongly to it, and we get a higher reward. This also reinforces the strength of an addiction. This has implications for food, which is why a banana and a candy with the exact same amount of sugar make us feel differently. The candy which instantly digests and gives us a sudden jolt of sugar, is highly addictive. The banana, which takes time to digest and releases the same amount of sugar, just over time, is not addictive!
This principle also applies for drugs, and gets to the root of why ADHD medications are not addictive – usually. The medications used for ADHD tend to digest very slowly, and although they act on the brain in the exact same way as cocaine and crystal meth, are not addictive. This is because that, relative to drugs of abuse, the medications are released very slowly.
The exception can be if you use ADHD medications in ways they are not meant to be – such as snorting or injecting (neither of these are safe methods to use). By snorting/injecting, instead of digesting you get around the bodies need to digest, and you can get a sudden jolt of dopamine, which would potentially contribute to an addiction.
Dr. Travis Barron is a resident physician in Toronto, Canada.