Overview of substance use disorders and overdose

Last reviewed: 23 Aug 2023
Last updated: 01 Aug 2023

This page compiles our content related to substance use disorders and overdose. For further information on diagnosis and treatment, follow the links below to our full BMJ Best Practice topics on the relevant conditions and symptoms.



An opioid is a synthetic or natural agent that stimulates opioid receptors and produces opium-like effects. Opiates are a type of opioid that are naturally derived from the opium poppy (e.g., codeine, morphine, opium). They are used to treat pain but may also be misused because of their euphoric effects. Naturally-derived opiates are commonly used alongside semisynthetic and synthetic opioids such as fentanyl, heroin (diamorphine), methadone, oxycodone, and hydrocodone. The Diagnostic and statistical manual of mental disorders, 5th edition, text revision (DSM-5-TR) defines opioid use disorder as a problematic pattern of opioid use leading to clinically significant impairment or distress, as manifested by at least 2 out of 11 criteria within a 12-month period.[5]

Overdose occurs when larger quantities than physically tolerated are taken, resulting in central nervous system (CNS) and respiratory depression, miosis, and apnea. Can be fatal if not treated rapidly.

Cocaine is a controlled illicit, highly addictive stimulant drug that is usually either insufflated (snorted), injected, or smoked in its freebase form (crack). Cocaine use is normally occasional, with the majority of users not meeting the criteria for cocaine use disorder. The DSM-5-TR classifies cocaine use disorder as mild, moderate, or severe defined by the number of symptoms within a 12-month period.[5] Chronic use can lead to scarring of heart tissue and myocardial hypertrophy and other changes collectively known as myocardial remodeling. These changes constitute the substrate for the occurrence of lethal arrhythmias. Cocaine use causes a hyperadrenergic state associated with abnormal mentation. The symptoms of any hyperadrenergic state include nausea, jitteriness, trouble concentrating, anxiety, paranoia, and euphoria. 

Refers to adverse events that occur within minutes or hours of excessive cocaine use. These events, which can occur in combination or isolation, include hyperthermia, rhabdomyolysis, dysrhythmia, ischemia, intracranial hemorrhage, agitation, psychosis, and seizures.

Some patients may die suddenly before treatment can be given.

Amphetamine and methamphetamine are noncatecholamine sympathomimetic amines that may be taken by various routes including inhalation, intravenous, intramuscular, or transmucosal (oral/nasal). Amphetamine and methamphetamine use disorders involve compulsive substance use despite negative consequences. Polysubstance use, for example with opioids, is an increasing problem, and increases mortality.

Patients with amphetamine toxicity will often present with agitated, irrational, restless, and aggressive behavior, and may show signs of hypervigilance, paranoia, and psychosis.[6] Overdose and toxicity strike inconsistently among new, occasional, chronic, and binge users. Intentional overdose is also encountered.

Cannabis use disorder

Cannabis is the most commonly used drug worldwide, with an estimated 219 million users in 2021.[1] Acute health effects include impaired cognitive and psychomotor performance. Chronic health effects may include sustained cognitive impairment (and impaired cognitive development in children and adolescents), dependence, increased risk of schizophrenia and social anxiety, exacerbation of bipolar disorders, worsened respiratory symptoms, and increased frequency of chronic bronchitis associated with smoking cannabis.[7]

Inhalant use disorder

The deliberate inhalation of a volatile substance to achieve an altered mental state.[8] Inhalants used include volatile solvents from household and industrial products; aerosol propellants; gases from household, industrial, and medical products; and nitrites and nitrous oxide. Hypoxia and heart failure can occur within minutes. Longer-term adverse effects include hearing loss, peripheral neuropathies, and liver and kidney damage. The DSM-5-TR restricts its definition of inhalant use disorder to volatile hydrocarbon-based substances; other volatile substances, including nitrous oxide, are included in other (or unknown) substance use disorder.[5]

Hallucinogen use disorder

The DSM-5-TR divides problematic hallucinogen use into two categories: phencyclidine use disorder and other hallucinogen use disorder.[5] Phencyclidine use disorder includes pharmacologically similar substances such as ketamine, cyclohexamine, and dizocilpine. Other hallucinogen use disorder covers a diverse group of substances including phenylalkylamines (e.g., mescaline, MDMA), indoleamines (e.g., psilocybin, dimethyltryptamine [DMT]), ergolines (e.g., LSD), and hallucinogenic plants (e.g., Salvia divinorum, jimsonweed).[5] Psychological effects can be unpredictable. Long-term adverse effects of hallucinogens are rare, but may include persistent psychosis or hallucinogen persisting perception disorder.[9]

Overdose can be intentional (e.g., as an act of self-harm), as part of recreational misuse, or accidental (e.g., medication error). The key feature of overdose is excessive sedation. Larger doses can cause coma, respiratory depression, and, without appropriate treatment, even death, particularly in the context of mixed ingestion with other CNS depressants.

Tricyclic antidepressants have a narrow therapeutic index and therefore become potent cardiovascular and CNS toxins in moderate doses. Best markers for suspected overdose are a history of depression, suicidality, and overdose, with a sudden deterioration in mental status and vital signs.

The use of testosterone derivatives to improve athletic performance or to increase lean body mass and muscle size. Misuse differs from that of other drugs, such as heroin or cocaine, as the desire to use them does not generally come from effects of the drug, but rather from wanting to change appearance or improve athletic performance. They are used at doses 10 to 100 times higher than those required to treat medical conditions.

Overdose may occur after excessive ingestion of acetaminophen or acetaminophen-containing medication as an acute or staggered overdose, or therapeutic excess. Untreated acetaminophen poisoning may cause varying degrees of liver injury over the 1 to 4 days following ingestion, including fulminant hepatic failure. Patients are often asymptomatic or have only mild gastrointestinal symptoms at initial presentation. Rarely, massive overdose may initially present with coma and severe metabolic acidosis.

Alcohol-use disorder, particularly when chronic and severe, can be associated with a variety of medical and psychiatric sequelae. In 2016, harmful alcohol use resulted in an estimated 3 million deaths globally.[10] Unintentional injuries, digestive diseases, and alcohol use disorders are the leading contributors to the alcohol-related burden of disease.[10]

Cigarette smoking is the most common cause of preventable death and disease.[11] Physicians and other healthcare professionals should play a central role in motivating and assisting patients who smoke to stop.[12]

Children may ingest a toxic substance accidentally while exploring their environment, or deliberately in response to stress or underlying mental problems, or in an attempt to get "high." Agents consumed may be pharmaceutical substances; drugs of abuse (including alcohol); toxic plants, berries, or mushrooms; or chemicals. Diagnosis is based on a combination of thorough clinical evaluation and comprehensive laboratory investigation to identify all ingested substances.



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This overview has been compiled using the information in existing sub-topics.

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