Substance use disorders and addiction

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What is drug addiction?

Addiction is defined as a chronic, relapsing brain disease that is characterized by compulsive drug seeking and use, 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.

 

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 neuro-transmitters 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 stimulation of the brain’s pleasure circuit teach us to keep taking drugs?

Our brains are wired to ensure that we will repeat life-sustaining activities by associating those activities with pleasure or reward. Whenever this reward circuit is activated, the brain notes that something important is happening that needs to be remembered, and teaches us to do it again and again without thinking about it. Because drugs of abuse stimulate the same circuit, we learn to abuse drugs in the same way.Why are drugs more addictive than natural rewards?When some drugs of abuse are taken, they can release 2 to 10 times the amount of dopamine that natural rewards such as eating and sex do. In some cases, this occurs almost immediately (as when drugs are smoked or injected), and the effects can last much longer than those produced by natural rewards. The resulting effects on the brain’s pleasure circuit dwarf those produced by naturally rewarding behaviors. The effect of such a powerful reward strongly motivates people to take drugs again and again. This is why scientists sometimes say that drug abuse is something we learn to do very, very well.

 

What happens to your brain if you keep taking drugs?

For the brain, the difference between normal rewards and drug rewards can be described as the difference between someone whispering into your ear and someone shouting into a microphone. Just as we turn down the volume on a radio that is too loud, the brain adjusts to the overwhelming surges in dopamine (and other neurotransmitters) by producing less dopamine or by reducing the number of receptors that can receive signals. As a result, dopamine’s impact on the reward circuit of the brain of someone who abuses drugs can become abnormally low, and that per-son’s ability to experience any pleasure is reduced. This is why a person who abuses drugs eventually feels flat,lifeless, and depressed, and is unable to enjoy things that were previously pleasurable. Now, the person needs to keep taking drugs again and again just to try and bring his or her dopamine function back up to normal—which only makes the problem worse, like a vicious cycle. Also, the person will often need to take larger amounts of the drug to produce the familiar dopamine high—an effect known as tolerance.

 

How does long-term drug taking affect brain circuits?

We know that the same sort of mechanisms involved in the development of tolerance can eventually lead to profound changes in neurons and brain circuits, with the potential to severely compromise the long-term health of the brain. For example, glutamate is another neurotransmitter that influences the reward circuit and the ability to learn. When the optimal concentration of glutamate is altered by drug abuse, the brain attempts to compensate for this change, which can cause impairment in cognitive function.Similarly, long-term drug abuse can trigger adaptations in habit or non-conscious memory systems. Conditioning is one example of this type of learning, in which cues in a person’s daily routine or environment become associated with the drug experience and can trigger uncontrollable cravings whenever the person is exposed to these cues,even if the drug itself is not available. This learned “reflex” is extremely durable and can affect a person who once used drugs even after many years of abstinence.

 

What other brain changes occur with drug abuse?

Chronic exposure to drugs of abuse disrupts the way critical brain structures interact to control and inhibit behaviors related to drug use.Just as continued abuse may lead to tolerance or the need for higher drug dosages to produce an effect, it may also lead to addiction, which can drive a user to seek out and take drugs compulsively. Drug addiction erodes a person’s self-control and ability to make sound decisions, while producing intense impulses to take drugs.

 

What are the medical consequences of drug addiction?

People who suffer from addiction often have one or more accompanying medical issues, which may include lung or cardiovascular dis-ease, stroke, cancer, and mental disorders. Imaging scans, chest X-rays, and blood tests show the damaging effects of long-term drug abuse throughout the body. For example, research has shown that tobacco smoke causes cancer of the mouth, throat, larynx, blood,lungs, stomach, pancreas, kidney, bladder, and cervix. In addition, some drugs of abuse, such as inhalants, are toxic to nerve cells and may damage or destroy them either in the brain or the peripheral nervous system.Does drug abuse cause mental disorders, or vice versa?Drug abuse and mental illness often co-exist. In some cases, mental disorders such as anxiety,depression, or schizophrenia may precede addiction; in other cases, drug abuse may trigger or exacerbate those mental disorders, particularly in people with specific vulnerabilities.

 

What are some effects of specific abused substances?

Nicotine is an addictive stimulant found in cigarettes and other forms of tobacco. Tobacco smoke increases a user’s risk of cancer, emphysema, bronchial disorders, and cardiovascular disease. The mortality rate associated with tobacco addiction is staggering. Tobacco use killed approximately 100 mil-lion people during the 20th century, and, if current smoking trends continue, the cumulative death toll for this century has been projected to reach 1 billion.

Alcohol consumption can damage the brain and most body organs. Areas of the brain that are especially vulnerable to alcohol-related damage are the cerebral cortex (largely responsible for our higher brain functions, including problem solving and decision making), the hippocampus (important for memory and learning), and the cerebellum (important for movement coordination).

Marijuana impairs short-term memory and learning, the ability to focus attention,and coordination. It also increases heart rate, can harm the lungs, and can increase the risk of psychosis in those with an underlying vulnerability.

Prescription medications, including opioid pain relievers, anti-anxiety sedatives, and ADHD stimulants are commonly misused to self-treat for medical problems or abused for purposes of getting high or (especially with stimulants) improving performance. However, misuse or abuse of these drugs (that is, taking them other than exactly as instructed by a doctor and for the purposes prescribed) can lead to addiction and even, in some cases, death. Opioid pain relievers, for instance, are frequently abused by being crushed and injected or snorted, greatly raising the risk of addiction and overdose. Unfortunately, there is a common misperception that because medications are prescribed by physicians, they are safe even when used illegally or by another person than they were prescribed for.

Inhalants are volatile substances found in many household products, such as oven cleaners, gasoline, spray paints, and other aerosols, that induce mind-altering effects; they are frequently the first drugs tried by children or young teens. Inhalants are extremely toxic and can damage the heart, kidneys, lungs, and brain. Even a healthy person can suffer heart failure and death within minutes of a single session of prolonged sniffing of an inhalant.

Cocaine is a short-acting stimulant, which can lead users to take the drug many times in a single session (known as a “binge”). Cocaine use can lead to severe medical consequences related to the heart and the respiratory, nervous, and digestive systems.

Amphetamines, including methamphetamine, are powerful stimulants that can produce feelings of euphoria and alertness. Methamphetamine’s effects are particularly long-lasting and harmful to the brain. Amphetamines can cause high body temperature and can lead to serious heart problems and seizures.

MDMA (Ecstasy or “Molly”) produces both stimulant and mind-altering effects. It can increase body temperature, heart rate, blood pressure, and heart-wall stress. MDMA may also be toxic to nerv ecells.

LSD is one of the most potent hallucinogenic, or perception altering, drugs. Its effects are unpredictable, and abusers may see vivid colors and images, hear sounds, and feel sensations that seem real but do not exist. Users also may have traumatic experiences and emotions that can last for many hours.

Heroin is a powerful opioid drug that produces euphoria and feelings of relaxation. It slows respiration, and its use is linked to an increased risk of serious infectious diseases, especially when taken intravenously.  People who become addicted to opioid pain relievers sometimes switch to heroin instead, because it produces similar effects and may be cheaper or easier to obtain.

Steroids, which can also be prescribed for certain medical conditions, are abused to increase muscle mass and to improve athletic performance or physical appearance. Serious consequences of abuse can include severe acne, heart disease, liver problems, stroke, infectious diseases, depression, and suicide.

Drug combinations. A particularly dangerous and common practice is the combining of two or more drugs. The practice ranges from the co-administration of legal drugs, like alcohol and nicotine, to the dangerous mixing of prescription drugs, to the deadly combination of heroin or cocaine with fentanyl(an opioid pain medication). Whatever the context, it is critical to realize that because of drug–drug interactions, such practices often pose significantly higher risks than the already harmful individual drugs.

 

Can addiction be treated successfully?

YES. Addiction is a treatable disease. Research in the science of addiction and the treatment of substance use disorders has led to the development of evidence-based interventions that help people stop abusing drugs and resume productive lives.

 

Does relapse to drug abuse mean treatment has failed?

No. The chronic nature of the disease means that relapsing to drug abuse at some point is not only possible, but likely. Relapse rates (i.e.,how often symptoms recur) for people with addiction and other substance use disorders are similar to relapse rates for other well-under-stood chronic medical illnesses such as diabetes, hypertension, and asthma, which also have both physiological and behavioral components. Treatment of chronic diseases involves changing deeply imbedded behaviors, and relapse does not mean treatment has failed. For a person recovering from addiction, lapsing back to drug use indicates that treatment needs to be reinstated or adjusted or that another treatment should be tried.

NIH Pub No. 14-5605

 

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