Drug addiction is a chronic disease characterized by drug seeking and use that is compulsive, or difficult to control, despite harmful consequences. It is considered a brain disease because drugs change the brain—they change its structure and how it works.
These brain changes can be long-lasting, and can lead to the harmful behaviors seen in people who abuse drugs. Brain changes that occur over time with drug use challenge an addicted person’s self-control and interfere with their ability to resist intense urges to take drugs.
The initial decision to take drugs is voluntary for most people, but repeated drug use can lead to brain changes that challenge an addicted person’s self-control and interfere with their ability to resist intense urges to take drugs.
What happens to the brain when a person takes drugs?
Most drugs affect the brain’s “reward circuit” by flooding it with the chemical messenger dopamine. This reward system controls the body’s ability to feel pleasure and motivates a person to repeat behaviors needed to thrive, such as eating and spending time with loved ones. This overstimulation of the reward circuit causes the intensely pleasurable “high” that can lead people to take a drug again and again.
As a person continues to use drugs, the brain adjusts to the excess dopamine by making less of it and/or reducing the ability of cells in the reward circuit to respond to it. This reduces the high that the person feels compared to the high they felt when first taking the drug—an effect known as tolerance. They might take more of the drug, trying to achieve the same dopamine high. It can also cause them to get less pleasure from other things they once enjoyed, like food or social activities.
Why do people take drugs?
In general, people begin taking drugs for a variety of reasons:
To feel good. Most abused drugs produce intense feelings of pleasure. This initial sensation of euphoria is followed by other effects, which differ with the type of drug used. For example, with stimulants such as cocaine, the “high” is followed by feelings of power, self-confidence, and increased energy. In contrast, the euphoria caused by opiates such as heroin is followed by feelings of relaxation and satisfaction.
To feel better. Some people who suffer from social anxiety, stress-related disorders, and depression begin abusing drugs in an attempt to lessen feelings of distress. Stress can play a major role in beginning drug use, continuing drug abuse, or relapse in patients recovering from addiction.
Drugs and the Brain
The human brain is the most complex organ in the body. This three-pound mass of gray and white matter sits at the center of all human activity—you need it to drive a car, to enjoy a meal, to breathe, to create an artistic masterpiece, and to enjoy everyday activities. In brief, the brain regulates your body’s basic functions; enables you to interpret and respond to everything you experience; and shapes your thoughts, emotions, and behavior.
The brain is made up of many parts that all work together as a team. Different parts of the brain are responsible for coordinating and performing specific functions. Drugs can alter important brain areas that are necessary for life-sustaining functions and can drive the compulsive drug abuse that marks addiction.
How do drugs work in the brain?
Drugs are chemicals that affect the brain by tapping into its communication system and interfering with the way neurons normally send, receive, and process information. Some drugs, such as marijuana and heroin, can activate neurons because their chemical structure mimics that of a natural neurotransmitter. This similarity in structure “fools” receptors and allows the drugs to attach onto and activate the neurons. Although these drugs mimic the brain’s own chemicals, they don’t activate neurons in the same way as a natural neurotransmitter, and they lead to abnormal messages being transmitted through the network.
Other drugs, such as amphetamine or cocaine, can cause the neurons to release abnormally large amounts of natural neurotransmitters or prevent the normal recycling of these brain chemicals. This disruption produces a greatly amplified message, ultimately disrupting communication channels.
How do drugs work in the brain to produce pleasure?
Most drugs of abuse 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 regulate movement, emotion, motivation, and feelings of pleasure. When activated at normal levels, this system rewards our natural behaviors. Overstimulating the system with drugs, however, produces euphoric effects, which strongly reinforce the behavior of drug use—teaching the user to repeat it.
How does cocaine affect the brain?
Cocaine increases levels of the natural chemical messenger dopamine in brain circuits controlling pleasure and movement.
Normally, the brain releases dopamine in these circuits in response to potential rewards, like the smell of good food. It then recycles back into the cell that released it, shutting off the signal between nerve cells. Cocaine prevents dopamine from recycling, causing excessive amounts to build up between nerve cells. This flood of dopamine ultimately disrupts normal brain communication and causes cocaine’s high.
What effects does heroin have on the body?
Heroin binds to and activates specific receptors in the brain called mu-opioid receptors (MORs). Our bodies contain naturally occurring chemicals called neurotransmitters that bind to these receptors throughout the brain and body to regulate pain, hormone release, and feelings of well-being. When MORs are activated in the reward center of the brain, they stimulate the release of the neurotransmitter dopamine, causing a sensation of pleasure. The consequences of activating opioid receptors with externally administered opioids such as heroin (versus naturally occurring chemicals within our bodies) depend on a variety of factors: how much is used, where in the brain or body it binds, how strongly it binds and for how long, how quickly it gets there, and what happens afterward.
Alcohol and the Brain
Alcohol affects brain chemistry by altering levels of neurotransmitters. Alcohol increases the effects of the inhibitory neurotransmitter GABA in the brain. GABA causes the sluggish movements and slurred speech that often occur in alcoholics. At the same time, alcohol inhibits the excitatory neurotransmitter glutamate. Suppressing this stimulant results in a similar type of physiological slowdown. In addition to increasing the GABA and decreasing the glutamate in the brain, alcohol increases the amount of the chemical dopamine in the brain’s reward center, which creates the feeling of pleasure that occurs when someone takes a drink.