Merck Manual

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Substance Use Disorders

(Addiction)

By

Mashal Khan

, MD, Weill Cornell Medicine

Medically Reviewed Oct 2022
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Substance use disorders generally involve behavior patterns in which people continue to use a substance (for example, a recreational drug) despite having problems caused by its use.

The substances involved tend to be members of the 10 classes of drug that typically cause substance-related disorders:

The specific manifestations and treatment of intoxication and withdrawal vary by the substance or substance class and are discussed elsewhere in THE MANUAL.

The common terms "addiction," "abuse," and "dependence" are too loosely and variably defined to be very useful in systematic diagnosis; "substance use disorder" is more comprehensive and has fewer negative connotations.

Physiologic Effects of Substance Use

These substances all directly activate the brain's reward system and produce feelings of pleasure. The activation may be so strong that people intensely crave the substance. They may neglect normal activities to obtain and use the drug. These substances also have direct physiologic effects, including

  • Intoxication

  • Withdrawal

  • Substance-induced mental health disorders

Intoxication

Intoxication refers to the immediate and temporary effects of a specific drug. Intoxication impairs the person's mental function and judgment and may alter mood. Depending on the drug, the person may feel a sense of excitement or an exaggerated feeling of well-being (or euphoria), or the person may feel calmer, more relaxed, and sleepier than usual.

Many drugs impair physical functioning and coordination, leading to falls and vehicle crashes. Some drugs trigger aggressive behavior, leading to fighting. As larger amounts of the drug are used (called an overdose), adverse effects become more obvious, with serious complications and sometimes risk of death.

Withdrawal

Withdrawal refers to symptoms that develop when people stop taking a substance or take significantly less than usual. Withdrawal causes various unpleasant symptoms that differ depending on the substance involved. Withdrawal from some drugs (such as alcohol Alcohol Use Alcohol (ethanol) is a depressant (it slows down brain and nervous system functioning). Consuming large amounts rapidly or regularly can cause health problems, including organ damage, coma,... read more or barbiturates Misuse of Antianxiety Medications and Sedatives Antianxiety and sedative medications are prescription drugs used to relieve anxiety and/or help with sleep, but their use can result in dependency and a substance use disorder. Using prescription... read more ) can be serious and even life threatening. Most people who experience withdrawal know that taking more of the substance will reduce their symptoms.

Whether withdrawal occurs depends only on the substance and how long it is used, not whether the person has a substance use disorder Substance Use Disorders Substance use disorders generally involve behavior patterns in which people continue to use a substance (for example, a recreational drug) despite having problems caused by its use. The substances... read more , is using the substance recreationally, or the substance is illegal. Some prescription drugs, particularly opioids, sedatives, and stimulants, can result in withdrawal symptoms even when taken as prescribed for legitimate medical reasons and for relatively brief periods (less than 1 week for opioids).

People who have withdrawal symptoms were previously termed physically dependent upon the substance. However, "dependence" has negative connotations suggesting illicit drug use, so doctors prefer to avoid this terminology.

Substance-Induced Mental Health Disorders

For a mental health disorder to be considered substance induced, the substance involved must be known to be capable of causing the disorder. Substances can be members of the 10 classes of drug that typically cause substance-related disorders:

But many other substances can cause mental health disorders. Common examples include anticholinergic drugs Anticholinergic: What Does It Mean? Anticholinergic: What Does It Mean? and corticosteroids, which may cause temporary symptoms of psychosis.

In addition, the mental health disorder should

* Certain disorders of thinking caused by alcohol, inhalants, or sedatives/hypnotics, and perceptual disorders caused by hallucinogens may be long lasting.

Medical Care for Recreational and Illicit Substance Use

Use of illegal drugs, although problematic from a legal standpoint, does not always involve a substance use disorder. On the other hand, legal substances, such as alcohol and prescription drugs (and marijuana in an increasing number of states in the United States), may be involved in a substance use disorder. Problems caused by use of prescription and illegal drugs cut across all socioeconomic groups.

Recreational drug use has existed in one form or another for centuries. People have used drugs for a variety of reasons, including

  • To alter or enhance mood

  • As part of religious ceremonies

  • To gain spiritual enlightenment

  • To enhance performance

People who take drugs recreationally may take them occasionally in relatively small doses, often without doing themselves harm. That is, users do not develop drug withdrawal Withdrawal Substance use disorders generally involve behavior patterns in which people continue to use a substance (for example, a recreational drug) despite having problems caused by its use. The substances... read more , and the drug does not physically harm them (at least in the short term). Drugs usually considered recreational include opium, alcohol, nicotine, marijuana, caffeine, hallucinogenic mushrooms Hallucinogens Hallucinogens are a class of drugs that cause profound distortions in people's perceptions. Hallucinogens distort and intensify sensations, but the actual effects are variable and unpredictable... read more (see also Mushroom [Toadstool] Poisoning Mushroom (Toadstool) Poisoning Many species of mushroom are poisonous and can cause different symptoms depending on the type of mushroom. Different species of mushrooms produce different toxins with different effects Even... read more ), and cocaine. Many recreational drugs are considered "natural" because they are close to their plant origin. They contain a mixture of low-concentration psychoactive ingredients rather than an isolated, more concentrated psychoactive compound.

Recreational drugs are can be taken by mouth, inhaled, or injected.

Causes of Substance Use Disorders

People usually progress from experimentation to occasional use and then to heavy use and sometimes to a substance use disorder. This progression is complex and only partially understood. The process depends on interactions between the drug, user, and setting.

Drug

Drugs in the 10 classes vary in how likely they are to cause a substance use disorder. The likelihood is termed addiction liability. Addiction liability depends upon a combination of factors including

In addition, substances that are legally and/or readily available, such as alcohol Alcohol Use Alcohol (ethanol) is a depressant (it slows down brain and nervous system functioning). Consuming large amounts rapidly or regularly can cause health problems, including organ damage, coma,... read more and tobacco Tobacco Use , are more likely to be used first. As people continue to use a substance, they often see less risk in using it and may begin to increase their use and/or experiment with other substances. People's perception of risk also may be influenced by the social and legal consequences of use.

During treatment of medical illness or following surgical or dental procedures, people are routinely prescribed opioids. If people do not take the whole amount prescribed, the drugs sometimes end up in the hands of people who wish to use them recreationally. Because the use of these drugs for nonmedical purposes has become such a large problem, many health care providers have responded by

  • Prescribing lower amounts of opioid drugs

  • Encouraging people to safely store or dispose of any leftover drugs

  • Expanding prescription take-back programs

User

Factors in users that may predispose to a substance use disorder include

  • Psychologic characteristics

  • Circumstances and disorders

Psychologic characteristics are not clearly a strong factor, although people with low levels of self-control (impulsivity) or high levels of risk-taking and novelty-seeking behaviors may have an increased risk of developing a substance use disorder. However, there is little scientific evidence to support the concept of the "addictive personality" that has been described by some behavioral scientists.

A number of circumstances and coexisting disorders appear to increase the risk of a substance use disorder. For example,

Addiction likely has many causes, some of which are genetic and other of which are epigenetic (effects of behaviors and the environment carried with the genes). Research into specific genetic abnormalities varies by the specific substance. Researchers have found few biochemical or metabolic differences between people who do and do not develop substance use disorder.

Setting

Cultural and social factors are very important in initiating and maintaining (or relapsing to) substance use. Watching family members (eg, parents, older siblings) and peers using substances increases the risk that people will begin using substances. Peers are a particularly powerful influence among adolescents (see Substance Use in Adolescents Substance Use in Adolescents Substance use among adolescents ranges from experimentation to severe substance use disorders. All substance use, even experimental use, puts adolescents at risk of short-term problems, such... read more ). People who are trying to stop using a substance find it much more difficult if they are around others who also use that substance.

Doctors may inadvertently contribute to harmful use of psychoactive drugs by overzealously prescribing them to relieve stress. Many social factors, including mass media, contribute to the expectation that drugs should be used to relieve all distress.

Diagnosis of Substance Use Disorders

  • A doctor's evaluation

Sometimes a substance use disorder is diagnosed when people go to a health care practitioner because they want help stopping use of a drug. Other people try to hide their drug use, and doctors may suspect problems with drug use only when they notice changes in a person's mood or behavior. Sometimes doctors discover signs of substance use during a physical examination. For example, they may discover track marks caused by repeatedly injecting drugs intravenously. Track marks are lines of tiny, dark dots (needle punctures) surrounded by an area of darkened or discolored skin. Injecting drugs under the skin causes circular scars or ulcers. People may claim other reasons for the marks, such as frequent blood donations, bug bites, or other injuries.

Health care practitioners also use other methods (such as questionnaires) to identify a substance use disorder. Urine and sometimes blood tests may be done under certain circumstances to check for the presence of drugs.

Criteria for diagnosis

The criteria for diagnosing a substance use disorder fall into four categories. People who have 2 or more of these criteria within a 12-month period are considered to have a substance use disorder:

  • The person cannot control use of the substance.

  • The person's ability to meet social obligations is compromised by use of the substance.

  • The person uses the substance in physically dangerous situations.

  • The person shows physical signs of use and/or dependence.

Inability to control use

  • The person takes the substance in larger amounts or for a longer time than originally planned.

  • The person desires to stop or cut down use of the substance.

  • The person spends a lot of time obtaining, using, or recovering from the effects of the substance.

  • The person craves the substance.

Social impairment

  • The person fails to fulfill major role obligations at work, school, or home.

  • The person continues to use the substance even though it causes (or worsens) social or interpersonal problems.

  • The person gives up or reduces important social, occupational, or recreational activity because of substance use.

Risky use

  • The person uses the substance in physically hazardous situations (eg, when driving or in dangerous social circumstances).

  • The person continues to use the substance despite knowing it is worsening a medical or psychologic problem.

Physical symptoms

Note that some drugs, particularly opioids, sedative/hypnotics, and stimulants, can result in tolerance and/or withdrawal symptoms even when taken as prescribed for legitimate medical reasons and for relatively brief periods (less than 1 week for opioids). Withdrawal symptoms that develop following appropriate medical use do not warrant the diagnosis of a substance use disorder. For example, when people with severe pain due to advanced cancer become dependent (psychologically and physically) on an opioid such as morphine, their withdrawal symptoms are not considered evidence of a substance use disorder.

The severity of the substance use disorder is determined by the number of criteria met:

  • Mild: 2 to 3 criteria

  • Moderate: 4 to 5 criteria

  • Severe: 6 criteria

Treatment of Substance Use Disorders

  • Varies depending on substance and circumstances

Specific treatment depends on the drug being used, but it typically involves counseling and sometimes involves use of other drugs. Family support and support groups help people remain committed to stopping use of the drug.

Substance use disorders have become widespread and have resulted in a rising number of deaths. In response to this growing epidemic, many organizations have established harm-reduction programs to provide education, counseling, and referral for treatment. Their purpose is to reduce the harm of drug use in users who cannot stop. Some provide national telephone helplines.

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