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What Is Drug Dependency?

Drug dependency is a chronic, often relapsing condition that causes compulsive drug seeking and use, despite harmful consequences to the addicted person’s life. Although the initial decision to take drugs is voluntary for most people, the brain changes that occur over time affect an addicted person’s self-control and their ability to resist intense impulses to take drugs.

Fortunately, treatments are available to help people deal with addiction’s powerful disruptive effects. Research shows that combining addiction treatment medications with behavioral therapy is seen to provide successful results for many people with addictions and can result in lasting change and recovery. 

Like other chronic, relapsing diseases, such as diabetes, asthma, or heart disease, drug addiction can be managed successfully. And like with other chronic diseases, it is not uncommon for a person to relapse and begin abusing drugs again. Relapse, however, does not signal treatment failure—rather, it shows that treatment should be reinstated or adjusted or that an alternative treatment is needed to help the person regain control and recover.

What Happens to Your Brain When You Take Drugs?

Drugs contain 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: (1) by imitating the brain’s natural chemical

messengers and (2) by overstimulating the “reward circuit” of the


Some drugs (e.g., 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, like as cocaine or methamphetamine, can cause the nerve cells to release abnormally large amounts of natural neurotransmitters (mainly dopamine) or to stop the normal recycling of these brain chemicals, which is required to shut off the signaling between neurons. The result is a brain awash in dopamine, a neurotransmitter present in brain regions that control movement, emotion, motivation, and feelings of pleasure. The overstimulation of this reward system, which usually responds to natural behaviours linked to survival (eating, spending time with loved ones, etc.), produces euphoric effects in response to psychoactive drugs. This reaction sets up a reinforcing pattern that “teaches” people to repeat the rewarding behavior of abusing drugs.

As a person continues to abuse drugs, the brain adapts to the overwhelming surges in dopamine by producing less dopamine or by reducing the number of dopamine receptors in the reward circuit. The result is a reduction of dopamine’s impact on the reward circuit, which reduces the abuser’s ability to enjoy not only the drugs but also other events in life that used to bring pleasure. This decrease compels the addicted person to keep abusing drugs in an attempt to bring the dopamine function back to normal, but now larger amounts of the drug are needed to reach the same dopamine high—an effect known as tolerance.

Long-term abuse causes changes in other brain chemical systems and circuits as well. Glutamate is a neurotransmitter that influences the reward circuit and the ability to learn. When the optimal concentration of glutamate is affected by drug abuse, the brain tries to compensate, which can impair cognitive function. Brain imaging studies of drug-addicted people show changes in areas of the brain that are critical to judgment, decision making, learning and memory, and behaviour control. Together, these changes can lead abuser to seek out and take drugs compulsively despite adverse, even devastating consequences—which is the nature of addiction.

Why Do Some People Get Addicted While Other People Don't?

No one factor can predict if a person will become addicted to drugs. Risk for addiction is influenced by a combination of factors that include biology, social environment, and age or stage of development. The more risk factors a person has, the greater the chance that taking drugs can lead to addiction. For example:

  • Biology. The genes that people are born with—in combination with environmental influences—account for about half of their addiction vulnerability. Additionally, gender, ethnicity, and the presence of other mental disorders may influence risk for drug abuse and addiction.

  • Environment. A person’s environment includes many different influences, from family and friends to socioeconomic status and quality of life in general. Factors such as peer pressure, physical and sexual abuse, stress, and quality of parenting can greatly influence the occurrence of drug abuse and the escalation to addiction in a person’s life.

  • Development. Genetic and environmental factors interact with critical developmental stages in a person’s life to affect vulnerability to addiction. Although taking drugs at any age can lead to addiction, the earlier that drug use begins, the more likely it will progress to more serious abuse, which poses a specific challenge to adolescents. Because areas in their brains that control decision making, judgment, and self-control are still developing, adolescents may be especially prone to risk-taking behaviours, such as trying drugs of abuse.

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