Drugs, Dopamine, and the Reward System
Addictive drugs produce a high by overstimulating the brain’s Reward System. To explain more fully, some background about how the brain works is necessary.
Brain cells are called neurons. They communicate with one another through the exchange of minuscule molecules called neurotransmitters, which are like three-dimensional “keys” that fit into “locks,” called “receptors,” on the surface of brain cells. When a neurotransmitter locks onto a receptor, it transmits a message, either stimulating or depressing the neuron’s activity, depending on the neurotransmitter. The neuron responds and initiates a chain reaction of messages along interconnected bundles of nerve cells called “neural networks.” For these networks to operate properly, they must maintain proper balance among neurotransmitters. The brain has systems that detect imbalances and correct them.
The Reward System is the neural network involved in feeling pleasure. It’s also centrally involved in learning and motivation. The primary neurotransmitter in the Reward System is dopamine. If enough dopamine is released into the brain’s reward circuits, euphoria results.
Dopamine-based exhilaration is a common experience, at least partially responsible just about anytime one experiences pleasure. “A hug, a kiss, a word of praise or a winning poker hand”1 can trigger a dopamine spike and pleasure. When your sports team pulls out an improbable victory at the last second — think Joe Montana, Dwight Clark and “The Catch” — the delirium you feel if you’re a 49er fan is the rush of dopamine stimulating the brain’s Reward System.
Drugs create a high by increasing dopamine in the Reward System much more than natural rewards do — up to 10 times more.2 If drugs are used only occasionally, the brain’s corrective systems restore proper balance once the drugs wear off. But if drugs are used excessively, the brain boosts its defensive reaction. It does this through a process that leads to tolerance. Tolerance makes the Reward System less efficient, muting the overstimulation caused by drugs. Once tolerance develops, it takes more drugs to achieve the same high that used to be achieved with less.
If excessive drug use occurs over a long, continuous period, the brain develops accelerating tolerance. This can result in the permanent physical changes seen in the Reward System neurons of addicts. These changes alter not only the structure of those neurons, but also their function, literally changing how addicts think, resulting in behaviors like denial, irrationality and obsessive drug use.
The Reward System is an ancient part of the brain, pre-dating the evolution of rational brain networks. Thus, though the altered addict brain acts out in irrationally when it comes to drug use, it may be more accurate to describe that behavior as pre-rational.
1. Addiction is a Brain Disease, and It Matters, Science Magazine, October 3, 1997.