How Drugs Affect the Brain (Module 6)

Background

Different drugs have various effects on the body. People are motivated to take drugs because of the feeling of euphoria they experience as the drugs change the way the brain normally works. Some of the changes that happen in the brain following drug use are short-term, while other changes can last a long time.

Prolonged drug use can change the brain so that addiction results. Addiction is a disease caused by changes in the structure and functioning of the brain. Addiction is characterized by:

• A strong compulsion or drive to use drugs despite negative consequences (someone keeps using drugs even though he or she is having problems);
  
• Loss of control over amount of the drug used (using more than he or she plans) and over drug-related behavior (someone does or says things he or she would not ordinarily do);
  
• Intense craving for the drug when it is not available. This craving is due to changes in the brain. Once a person is addicted, he or she must have the drug just to keep from feeling bad. This is because drugs can cause changes in the functioning of neurotransmitters in the brain.
  
  

When a person stops using a drug, it takes a while for the brain to get back to normal. During that time, the person may feel bad and have intense craving for the drug. Research in animals and some humans is beginning to suggest that some drugs may cause changes that are permanent. Addiction is considered a disease because the drugs have changed the normal functioning of the brain. Addiction can be successfully treated. However, the best way to avoid addiction is to never start using drugs.

Cocaine
Cocaine is a stimulant made from the leaf of the coca plant. Cocaine speeds up activity in the brain and the spinal cord, causing an increase in blood pressure and heart rate and a decrease in the flow of blood and oxygen to the heart. When someone snorts, injects, or smokes cocaine, it travels to the brain very quickly. It reaches all areas of the brain but has its greatest effects in the front part of the cerebral cortex and on part of the limbic system.

A very complicated process takes place in the brain after it is exposed to cocaine. In a normal brain, the neurotransmitter dopamine is released by neurons to carry messages in the limbic system. After the message has been carried to the next neuron, dopamine is reabsorbed from the synapse back into the neuron that released it. Cocaine blocks the reabsorption of dopamine, leaving too much dopamine in the synapse. The excess dopamine is what causes the pleasurable feelings associated with taking cocaine and the increased motor activity seen with higher doses.

After a person abuses cocaine for a while, the brain tries to compensate for the excess dopamine, and the normal processes that take place are disrupted. The brain will no longer function normally without cocaine.

Marijuana
Marijuana is the dried leaves and flowers of the cannabis plant. More than 400 chemicals can be found in the average cannabis plant. The active ingredient in marijuana that produces changes in brain messages is called tetrahydrocannabinol (THC). The brain has receptors for a specific chemical, anandamide, which is naturally produced by the brain. THC is able to attach to and activate these same receptors. These receptors are called THC receptors rather than anandamide receptors because scientists knew that THC attaches to these receptors long before anandamide was discovered.

Scientists know less about how marijuana affects the nervous system than they do about other drugs. However, scientists know that some areas of the brain have a lot of THC receptors, while other areas have very few or none. When a person uses marijuana, the chemicals in the drug travel through the bloodstream and attach to the THC receptors, activating them and interfering with normal neurotransmission.

The areas of the brain with the most THC receptors are the cerebellum, the cerebral cortex, and the limbic system. This is why marijuana affects thinking, problem solving, sensory perception, movement, balance, and memory.

Alcohol
Alcohol is found in beer, wine, and spirits, e.g., gin, vodka, or whiskey. It affects the brain and almost every other organ in the body. The parts of the brain affected by alcohol are the cerebral cortex, limbic system, and brain stem. Alcohol interferes with messages carried by many neurotransmitters in the brain. Because these neurotransmitters are found throughout the brain, alcohol affects many functions, including thinking, coordination, and emotions.

If a person becomes dependent on alcohol, he or she might be diagnosed with the disease known as alcoholism. Alcoholism can be life-threatening. The long-term use of alcohol results in the depletion of certain vitamins and minerals in the body. These deficiencies can result in diseases like Wernicke-Korsakoff syndrome, a disease that affects the short-term memory and, in some cases, can result in a permanent loss of memory.

Nicotine
Nicotine comes from tobacco leaves and is found in all tobacco products—cigarettes, cigars, pipe and chewing tobacco, and snuff. Nicotine acts on the central and peripheral nervous systems. It also causes an increase in blood pressure, heart rate, and respiration.

Nicotine is shaped like the neurotransmitter acetylcholine, which is involved in movement, breathing, heart rate, learning, and memory. When nicotine gets into the brain, it hooks onto the place where acetylcholine would normally go and overexcites the brain.

Nicotine also affects the neurotransmitter dopamine. Scientists think that nicotine’s effects on dopamine are what cause the pleasurable sensations smokers experience. The long-term effects of smoking include lung cancer, emphysema, heart disease, and addiction. The longer a person smokes, the harder it is to quit. Fewer than 1 in 10 people who try to quit smoking actually succeed.