"Say What?" is a periodic series in which we define scientific terms and explain their importance.
Your brain is a communications center containing billions of neurons (nerve cells) that connect to each other in circuits—kind of like the circuits in a computer. Brain circuits coordinate everything you feel, think, and do.
Every neuron in your brain has hard-working receptors on its surface that receive signals from nearby neurons. And these receptors can be affected by drug use.
Getting the message
Neurons send and receive messages using molecules called neurotransmitters. When a neurotransmitter molecule is sent from one neuron to another, it attaches to a receptor on the receiving cell, kind of like a key in a lock.
Drugs upset the way neurons normally work. Some drugs (marijuana, heroin) “fool” receptors into thinking they’re another neurotransmitter produced in the body, and this causes abnormal messages to be sent through the brain circuit.
Jamming the circuits
Receptors are involved in tolerance, dependence, and addiction. If a person keeps taking drugs over time, their brain adjusts by producing fewer of its own neurotransmitters, or by reducing the number of receptors that can receive them. This creates an imbalance, and makes parts of the brain less sensitive—including its reward circuits, which are involved in addiction.
With less-sensitive reward circuits, a person who misuses drugs needs to keep taking more and more of them just to feel normal—which only makes the problem worse. It’s a vicious cycle.
Brain receptors help keep your senses, thoughts, and actions on track. But that can change if drugs interfere with the receptors’ job.
Learn why addiction is a disease.