Addictive drugs produce a high by over-stimulating the brain’s reward system. Addictive drugs hook us by creating a production of a brain chemical called dopamine.
The Art of Neurons
Neurons—aka brain cells—communicate with each other through the exchange of neurotransmitters. These are like three-dimensional keys; each fits a lock known as a “receptor.” When a neurotransmitter locks onto a receptor, it transmits a message. This message may stimulate the neuron’s activity, like how heroin depresses the opioid receptors which are responsible for pain regulation.
When a neuron responds to a neurotransmitter, it initiates a chain reaction of messages along interconnected bundles of nerve cells called “neural networks.” These networks can only operate properly if a proper balance of different neurotransmitters is maintained. The brain has systems which detect imbalances and work to correct them.
The Dopamine Factor
The reward system isn’t just responsible for feeling pleasure, but for learning and motivation, too. The main neurotransmitter for these processes is dopamine. A surge of dopamine in the brain’s circuits results in euphoria which is well remembered by the rest of the brain.
It’s not just drugs that cause dopamine to flood; a hug, a kiss, or word of praise, or a winning touchdown can also spike pleasure. Drugs like methamphetamine are simply far more powerful than any natural pleasure or rush—by at least 10 times. If drugs are only used occasionally, the brain can usually restore balance once the substances wear off.
The Self-Serving Illness
If the drugs are used excessively, the brain boosts its defensive reaction so strongly that it causes increased tolerance. This can lead to a vicious cycle in which the addict tries to compensate by consuming larger and larger doses, constantly straining the brain as it struggles to up its defenses. Over a long, continuous period, the brain develops accelerating tolerance, which can cause permanent physical changes seen in the central nervous system. These changes alter not only the structure of those neurons, but also their function. This is the phenomenon responsible for typical addict behavior like denial, irrationality, persistent sadness, and drug-obsession.