Addiction Treatment Blog

In part, that’s true, but most people find that their drug use escalates much faster than 7% a decade. Most people attribute the increased need for their substance or behaviour to tolerance, or what science calls neuro-adaptation. Before I tell you why I think addicts use more over time, I have to tell you a bit about tolerance.

Tolerance, neuro-adaptation, is when a nerve adjusts to a stimulating signal in order to go back to the way it was before it got the signal. For instance, let’s say that a guy who’s never had any alcohol takes a drink. Immediately, in order to keep him from failing over, his brain cells change the receptor that sees the alcohol. They’ve gotten too big a signal, and if the brain decreases the number of receptors that see alcohol, the signal will go down. Some tolerance is fast like that and some is slower, requiring about two weeks or so. Alcohol is the classic drug when you look at tolerance; the more you drink the more you are used to it, the more tolerant you are. So you can explain why an alcoholic who started drinking a six pack a day is 4 years later drinking a case a day and still feeling the same level of “drunk”. But what about a drug like cocaine? It doesn’t cause tolerance; it causes something like the opposite called sensitization. Why do cocaine users need more cocaine after using for a while if it causes the opposite of tolerance?

Now we come to what I think is the real reason we use more drug after a while. If it was tolerance, cocaine users would pick a dose and stick with it, but that doesn’t happen. The real reason I think we need more and more drug as time goes by (or more and more food, sex, gambling, just fill in the blank) is because of how the Nucleus Accumbens works. Remember I told you about the dopamine level in the Medial Forebrain Bundle and how the dopamine hits the Nucleus Accumbens? We called it the reward signal. What it more specifically and accurately encodes is not just reward but something called “Reward Prediction Error.” In a study at Columbia, researchers found that his area of the brain compares the current reward with the average reward and only fires when the current reward is greater than the expected average of what had come before.

So there’s an anticipatory rush when someone gets access to a drug that made them feel good before. They they use the drug. The Midbrain Dopamine cells calculate the difference between the reward they’re getting now and what they had gotten from prior experiences with the drug. If it isn’t better, there’s not as much signal Did you ever try to recapture a particular event that was really good? You did everything the same and still it wasn’t the same. That’s because the signal you got the first time was partly the surprise of a better than expected reward. The second time there was no extra punch because the reward wasn’t better than the average of what had come before. So that’s one of the reasons I think people use more and more drug over time regardless of whether the drug causes tolerance or not; the only way to boost the signal is to increase the unexpectedness of the stimulus.

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