Addiction and the Brain

As an intricate system of neurons, interconnected circuits, and messages, the brain oversees cognitive and bodily function allowing us to live our lives. Neurons send and receive signals that connect throughout the nervous system, including the brain, the spinal cord, and the rest of the peripheral nervous system. Messages are sent through neurotransmitters across the synaptic gap between neurons and are recycled by transporters. 

Substances like drugs and alcohol greatly influence the brain’s function by interfering with its circuitry and preventing full cognitive function. Some drugs can activate neurons, while others mimic the effect of natural chemicals. Altogether, dependence on substances affects the physical and psychological health of those suffering from addiction. 

Parts of the Brain 

Drugs alter the functioning of various parts of the brain. For instance, the basal ganglia are central to motivation through pleasurable activities which activate a reward circuit. Drugs, like cocaine, over-activate such circuits creating a false sense of euphoria. Such drugs deplete the brain’s supply of neurotransmitters dopamine, serotonin, and norepinephrine, while also causing intense crashing when they wear off. 

The prefrontal cortex is involved in higher-level cognition, including planning, problem-solving, decision making, and impulse control. Since the prefrontal cortex is the last part of the brain to mature, teenagers are the most vulnerable to substances as their decision-making and brain structure have not fully formed. 

Depressants vs. Stimulants 

Depressants refer to drugs that reduce neural activity and slow bodily functions, including alcohol, barbituates, and opiates. Alcohol slows neural processing leading to increased accident, and memory disruption. According to the National Institute on Alcohol Abuse and Alcoholism (2019 National Survey on Drug Use and Health), 25.8% of people ages 18 and older in the U.S. reported that they engaged in binge drinking in the past month. Moreover, they found that an estimated 95,000 people die from alcohol-related causes in the U.S., making it the third-leading preventable cause of death (behind tobacco and poor diet/lack of exercise). Between 2011 and 2015, the leading causes of alcohol-attributable deaths due to chronic conditions in the U.S. were liver disease, heart disease, liver cancer, hypertension, and stroke. 

Other types of depressants are opiates, which include morphine, heroin, codeine, fentanyl, methadone, and other opium derivatives. These drugs depress neural activity to temporarily reduce pain and anxiety. Opiates are highly addictive as repeated use causes the brain to eventually stop producing endorphins. As the brain lacks normal levels of pain-killing neurotransmitters, it craves the drug to feel comfortable, creating uncontrollable cravings and a learned reflex. Opiates work by binding to specific receptors in the brain, mimicking the effects of natural pain-relieving chemicals (drugs like these are called agonists). According to the Alcohol and Drug Foundation, the short-term effects of opium include euphoria, lower heart rate, impaired reflexes, and analgesia; some long-term effects include difficulty having children, increased risk of lead poisoning, tolerance, and dependence. 

In contrast, stimulants are drugs- including nicotine, cocaine, ecstasy, methamphetamine, and more- that excite neural activity and speed up bodily functions, such as increased blood sugar, heart rate, and breathing rate. Stimulants increase extracellular dopamine levels in the brain through interacting with dopamine transporter, thus inciting feelings of reward and pleasure. Stimulants also over-activate norepinephrine, which influences energy and alertness. 

One type of stimulant is ecstasy (MDMA), which is a synthetic stimulant and mild hallucinogen that produces euphoria. MDMA affects the brain by increasing dopamine (reward reinforces behaviors), norepinephrine (increases heart rate and blood pressure), and serotonin (affects mood, appetite, and sleep) while blocking reiptake. Some of its effects include suppressed immune system, impaired memory, slowed thoughts, dehydration, increased blood pressure, and death.  Research varies on whether MDMA is addictive, but some people report signs of addiction including withdrawal symptoms like fatigue, loss of appetite, depression, and trouble concentrating. 

Methamphetamines are a powerfully addictive drug that stimulates the central nervous system by speeding up bodily functions and reducing baseline levels of dopamine. Some of its aftereffects include insomnia, hypertension, seizures, depression, irritability, and violent outpburts. According to American Addiction Centers, methamphetamine use causes increased neuronal death: the decrease in the number of neurons in the central nervous system in the hippocampus (memory and learning), the striatum (movement and directed attention), the parietal cortex (visual and nonverbal memory), frontal and prefrontal cortex (cognition, problem-solving, and reasoning), and the cerebellum (movement). Addiction to his drug decreases white matter, making neurons less efficient in transmitting signals. 

One of the most common addictions is nicotine: a stimulating a highly addictive drug, often found in tobacco. According to the Substance Abuse and Mental Health Services Administration (SAMHSA) , tobacco use is the leading cause of preventable death, leading to lung cancer, heart disease, stroke, and other serious illnesses. The CDC “reports that cigarette smoking causes more than 480,000 deaths each year in the U.S. The SAMHSA reports that among users of nicotine products, “nearly two thirds of adolescents aged 12 to 17 (63.1%) vaped nicotine but did not use tobacco products,” showing a shift in how nicotine is accessed, especially among teenager. Smoking is extremely hard to quit as users develop tolerance and dependence with intense withdrawal symptoms. The effects of nicotine include increased alertness, increased heart rate, relaxed muscles, and decreased circulation. 

Tolerance and Dependence 

Tolerance refers to the diminishing effect with regular use of the same dose of a drug, requiring the user to take larger and larger doses before experiencing an effect. Tolerance is based on the brain’s neuroadaptation, which occurs when the brain chemistry adapts to offset the drug’s effect. This creates a vicious cycle where the user must take more and more of the drug to feel a normal level of reward and comfort. When someone with an addiction does not access the drug, they can experience withdrawal: the discomfort and distress that is caused by the discontinued use of an addictive drug. 

According to the American Psychiatric Association’s Diagnostic and Statistical Manual of Mental Disorders, the presence of three or more of these symptoms indicates a dependence on a substance: tolerance, withdrawal, taking the substance longer or in larger amounts, failure to regulate the use, devoting much time, normal activities abandoned, continued use despite worsened problems. Dependence can take the form of physical or psychological effects. 


Addiction is a chronic disorder with the heightened desire to re-experience the use of a substance or behavior, that can lead to brain changes. Those suffering from addiction will continue to use despite adverse consequences; the disorder cannot be overcome voluntarily and requires long-term treatment and support. Apart from drug or alcohol addiction, other common addictions include gambling addiction, sex/pornographic addiction, internet addiction, shopping addiction, and risky behavior addiction. Regardless of the type of addiction, it is crucial to support those in our lives who have an addiction through their recovery. It is important to be educated in the effects of substances and how to seek psychological help when needed. The Substance Abuse and Mental Health Services Administration has a National Helpline which you can call at 1-800-662-HELP (4357). 


The Beginner’s Guide to the Neuro-biology of Drug Use

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