Drugs are chemicals that tap into the brain’s communication system and disrupt the way nerve cells normally send, receive, and process information. There are at least two ways that drugs cause this disruption: by imitating the brain’s natural chemical messengers and/or by overstimulating the “reward circuit” of the brain.
Some drugs, such as marijuana and heroin, have a similar structure to chemical messengers called neurotransmitters, which are naturally produced by the brain. This similarity allows the drugs to “fool” the brain’s receptors and activate nerve cells to send abnormal messages. Other drugs, such as cocaine or methamphetamine, can cause the nerve cells to release abnormally large amounts of natural neurotransmitters or to prevent the normal recycling of these brain chemicals, which is needed to shut off the signal between neurons. This disruption produces a greatly amplified message that ultimately disrupts normal communication patterns.
Nearly all drugs, directly or indirectly, target the brain’s reward system by flooding the circuit with dopamine. Dopamine is a neurotransmitter present in regions of the brain that control movement, emotion, motivation, and feelings of pleasure. The overstimulation of this system, which normally responds to natural behaviors that are linked to survival (eating, spending time with loved ones, etc), produces euphoric effects in response to the drugs. This reaction sets in motion a pattern that “teaches” people to repeat the behavior of abusing drugs.
As a person continues to abuse drugs, the brain adapts to the dopamine surges by producing less dopamine or reducing the number of dopamine receptors. The user must therefore keep abusing drugs to bring his or her dopamine function back to ”normal” or use more drugs to achieve a dopamine high.
Long-term drug abuse causes changes in other brain chemical systems and circuits, as well. Brain imaging studies of drug-addicted individuals show changes in areas of the brain that are critical to judgment, decision-making, learning and memory, and behavior control. Together, these changes can drive an abuser to seek out and take drugs compulsively — in other words, to become addicted to drugs. This information is reported by the National Council on Alcoholism and Drug Dependence.