Drugs are chemicals. When someone puts these chemicals into their body, either by smoking, injecting, inhaling, or eating them, they tap into the brain’s communication system and tamper with the way nerve cells normally send, receive, and process information. Different drugs—because of their chemical structures—work differently. We know there are at least two ways drugs work in the brain:
- Imitating the brain’s natural chemical messengers
- Overstimulating the “reward circuit” of the brain
Some drugs, like marijuana and heroin, have chemical structures that mimic that of a neurotransmitter that naturally occurs in our bodies. In fact, these drugs can “fool” our receptors, lock onto them, and activate the nerve cells. However, they don’t work the same way as a natural neurotransmitter, and the neurons wind up sending abnormal messages through the brain, which can cause problems both for our brains as well as our bodies.
Other drugs, such as cocaine and methamphetamine, cause nerve cells to release too much dopamine, which is a natural neurotransmitter, or prevent the normal recycling of dopamine. This leads to exaggerated messages in the brain, causing problems with communication channels. It’s like the difference between someone whispering in your ear versus someone shouting in a microphone.
The “High” From Drugs/Pleasure Effect
Most drugs of abuse—nicotine, cocaine, marijuana, and others—affect the brain’s “reward” circuit, which is part of the limbic system. Normally, the reward circuit responds to feelings of pleasure by releasing the neurotransmitter dopamine. Dopamine creates feelings of pleasure. Drugs take control of this system, causing large amounts of dopamine to flood the system. This flood of dopamine is what causes the “high” or intense excitement and happiness (sometimes called euphoria) linked with drug use.
The Repeat Effect
Our brains are wired to make sure we will repeat healthy activities, like eating, by connecting those activities with feeling good. Whenever this reward circuit is kick-started, the brain notes that something important is happening that needs to be remembered, and teaches us to do it again and again, without thinking about it. Because drugs of abuse come in and “hijack” the same circuit, people learn to use drugs in the same way.
After repeated drug use, the brain starts to adjust to the surges of dopamine. Neurons may begin to reduce the number of dopamine receptors or simply make less dopamine. The result is less dopamine signaling in the brain—like turning down the volume on the dopamine signal. Because some drugs are toxic, some neurons also may die.
As a result, the ability to feel any pleasure is reduced. The person feels flat, lifeless, and depressed, and is unable to enjoy things that once brought pleasure. Now the person needs drugs just to bring dopamine levels up to normal, and more of the drug is needed to create a dopamine flood, or “high”—an effect known as “tolerance.”
Watch our video below: Why Are Drugs So Hard To Quit? for more.
Drug use can eventually lead to dramatic changes in neurons and brain circuits. These changes can still be present even after the person has stopped taking drugs. This is more likely to happen when a drug is taken over and over.