[18] Substance use disorders (SUDs) are highly prevalent and exact a large toll on individuals' health, well-being, and social functioning.

Long-lasting changes in brain networks involved in reward, executive function, stress reactivity, mood, and self-awareness underlie the intense drive to consume substances and the inability to control this urge in a person who suffers from addiction (moderate or severe SUD).

Similarly, most researchers in this and related areas (such as the etiology of psychopathology generally), emphasize that various causal factors interact and influence each other in complex and multifaceted ways.

[26] Many times, issues may be interconnected, people without jobs are most likely to abuse substances which then makes them unable to work.

Through a study conducted in 2021 about the effect childhood experiences have on future substance use, researchers found that there is a direct connection between the two factors.

Individuals that had experiences in their childhood which left them traumatized in some way had a much higher chance of substance abuse.

[1] Other common risk factors are being male, being under 25, having other mental health problems (with the latter two being related to symptomatic relapse, impaired clinical and psychosocial adjustment, reduced medication adherence, and lower response to treatment[29]), and lack of familial support and supervision.

Other psychological risk factors include high impulsivity, sensation seeking, neuroticism and openness to experience in combination with low conscientiousness.

"On the other hand, substance abuse is the use of drugs such as prescriptions, over-the-counter medications, or alcohol for purposes other than what they are intended for or using them in excessive amounts.

[8] Diagnosis usually involves an in-depth examination, typically by psychiatrist, psychologist, or drug and alcohol counselor.

[36] There are 11 diagnostic criteria which can be broadly categorized into issues arising from substance use related to loss of control, strain to one's interpersonal life, hazardous use, and pharmacologic effects.

Signs include physical changes such as weight gain or loss; tremors, and bloodshot eyes.

[8] There are additional qualifiers for stages of remission that are based on the amount of time an individual with a diagnosis of a SUD has not met any of the 11 criteria except craving.

[40] The index assesses potential problems in seven categories: medical, employment/support, alcohol, other drug use, legal, family/social, and psychiatric.

[41] There are several different screening tools that have been validated for use with adolescents, such as the CRAFFT, and with adults, such as CAGE, AUDIT and DALI.

[42] Laboratory tests to detect alcohol and other drugs in urine and blood may be useful during the assessment process to confirm a diagnosis, to establish a baseline, and later, to monitor progress.

[45] Lastly combined behavioral intervention (CBI), can be used which involves combining elements of alcohol interventions, motivational interviewing, and functional analysis to help the clinician identify skill deficits and high risk situations that are associated with drinking or drug use.

[48] Depending on the severity of use, and the given substance, early treatment of acute withdrawal may include medical detoxification.

Clinical leaders in recent years have attempted to tailor intervention approaches to specific influences that affect addictive behavior, using therapeutic interviews in an effort to discover factors that led a person to embrace unhealthy, addictive sources of pleasure or relief from pain.

[50][51] In addition, the same author suggests that social skills training adjunctive to inpatient treatment of alcohol dependence is probably efficacious.

Medication-assisted treatment (MAT) refers to the combination of behavioral interventions and medications to treat substance use disorders.

Medications, such as methadone and disulfiram, can be used as part of broader treatment plans to help a patient function comfortably without illicit opioids or alcohol.

[60] The general theory of a vaccine intended to "immunize" against drug addiction or other substance abuse is that it would condition the immune system to attack and consume or otherwise disable the molecules of such substances that cause a reaction in the brain, thus preventing the addict from being able to realize the effect of the drug.

[80] According to Statistics Canada (2018), approximately one in five Canadians aged 15 years and older experience a substance use disorder in their lifetime.

[82] Across the country, the ethnic group that is statistically the most impacted by substance use disorders compared to the general population are the Indigenous peoples of Canada.