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Substance use problems: Assessment

Determining the severity of the disorder

The severity of the substance use disorder is judged by its effects on various domains of the person's life. These include:

  • physical health
  • mental health and social functioning
  • financial impacts
  • failures in occupational, educational or other role responsibilities


The most severe form of intoxication is considered an overdose and is a medical emergency. It usually involves respiratory compromise, disorientation and a reduced level of consciousness. Overdose with stimulants is associated with psychosis, seizures and cardiac arrhythmias.


Severe withdrawal, especially from alcohol, is associated with delirium (delirium tremens) and is characterized by illusions, not visual hallucinations (i.e., misinterpreting environmental stimuli, for example, by mistaking a rope for a snake). Withdrawal may be complicated by seizures as well.

Severe opioid withdrawal is characterized by autonomic symptoms including diarrhea, vomiting, sweating and pilo-erection. Seizures or delirium are not part of the opioid withdrawal syndrome.


For tobacco use, the number of cigarettes smoked per day and how quickly someone smokes after waking is a guide to the level of dependence. People who smoke 10 or more cigarettes per day and have their first cigarette within five minutes of waking are considered severely dependent.

Verifying the substance use history

Substance use disorders are best diagnosed by a thorough interview corroborated by a third party and a focused physical examination. The diagnosis is often made prospectively and requires repeated visits. The following screening tests can support a diagnosis or exclude potential contributors to a patient's presentation.

Direct screening measures

Urine drug screening (UDS)

Urine is an ideal matrix to test for drugs of abuse. Patient consent is necessary except in emergencies. The more specific the request, the more likely the drug will be detected (e.g., oxycodone rather than opioid).

The presence or absence of a drug in UDS does not rule in or out a diagnosis of a substance use disorder. Depending on the time lapsed since last use and on laboratory method, urine concentration, contamination and cut-off thresholds, the drug may not be detected. Therefore, UDS results must be interpreted in light of the clinical presentation.


Breathalysers are rarely used in primary care. They are used more commonly in emergency room and law enforcement settings. However, they can be a useful tool in office-based withdrawal management.

  • Breathalysers detect blood alcohol concentration (BAC) in mg% (mg/100mL).
  • Alveolar concentration of alcohol correlates closely to blood alcohol level.
  • 1 mg% = 0.2175 mmol/L or 4.6 mg% =1 mmol/L.
  • It is a criminal offence in Canada to drive with a BAC of ≥ 80 mg%.
  • 160 mg% (equivalent to 34 mmol/L) is associated with clinically obvious intoxication in a non-tolerant individual.

Blood alcohol concentration can vary substantially for the same amount of alcohol depending on a person's age, race, gender, weight, genetic predisposition and metabolic rate. Because of differing alcohol tolerance among individuals, a breathalyser does not establish the person's level of intoxication. Someone with significantly high tolerance can experience withdrawal symptoms even at BAC that would cause relatively intolerant individuals to exhibit sign of intoxication.

Physical signs of substance use

The signs of substance use and substance use disorders are protean and depend on the type and number of drugs used, time since use and co-occurring psychiatric and physical disorders.

In acute care settings, it is important to assess vital signs, level of consciousness and level of orientation. The physical exam should focus on stigmata of drug use (e.g., "track marks"), usually related to the route of admission. Clinicians should correlate the observed level of impairment with the apparent level of consumption. They should have a high index of suspicion that other factors (i.e., subdural hematoma) might better account for or contribute to the clinical picture.

Specific signs related to specific substances include:

  • pinpoint pupils with altered levels of consciousness and hypoventilation: opioid use
  • goosebumps, lacrimation, yawning and chills: opioid withdrawal
  • ataxia and dysarthria: alcohol intoxication
  • tremors and sweats: alcohol withdrawal
  • restlessness, anorexia, paranoia and delusions: intoxication with stimulants
  • somnolence and increased hunger: withdrawal from stimulants

The physical examination is helpful but not diagnostic of a substance use disorder. It is more useful in determining the effects of substance use.

Indirect screening measures



Gamma glutamyl transferase (GGT) and mean cell volume (MCV) both have low sensitivity for detecting alcohol problems; thus, a normal value should not be used as evidence to rule out an alcohol problem. Nonetheless, these are useful measures to confirm clinical suspicion and to monitor treatment response. MCV normalizes after three months and GGT normalizes after four weeks.


Breath carbon monoxide monitor

The carbon monoxide (CO) found in cigarette smoke is absorbed via the lungs. CO competes with oxygen for hemoglobin, binding and displacing it, which results in less oxygen delivery to tissue and vital organs. A convenient office detector measures breath CO in parts per million as an indirect measure of serum carboxyhemoglobin level (COHb). It can be used in smoking cessation counselling as a motivator to illustrate the impact of the patient's cessation efforts or to verify self-reported smoking quantity. Other sources of CO (e.g., automobile exhaust) and time from last cigarette will affect readings. CO levels of greater than 3ppm are found in people who smoke.

Exploring the relationship between substance use and presentation

Consequences of substance use

In addition to quantifying the amount, frequency, route and duration of use, it is important to explore the consequences of substance use in the person's life. To make the diagnosis, cautiously explore the link between substance use and the presenting complaint.

Concurrent disorders

When patients who are abusing substances present with psychiatric symptoms, it may not be possible in the acute situation to differentiate between a substance-induced psychiatric disorder and a concurrent disorder.

Exploring the temporal relationship between substance use and psychiatric symptoms may be helpful. However, sometimes the relationship between substance use and psychiatric symptoms can only be determined after substance use is significantly reduced or after weeks of abstinence. The inability to determine whether the mental illness is distinct from the substance use disorder does not preclude treating the mental health issues concurrently with the substance use disorder.

Ruling out underlying organic pathology

When a patient presents with psychiatric symptoms, it is critical to rule out an organic condition that may mimic a mental illness. In the case of substance use, the substance itself is often the organic cause for the presentation. To differentiate symptoms that can be attributed to organic pathology, or substance use, or both, it may be necessary to observe the patient. For example:

  • A patient who is dependent on alcohol may appear to be acutely intoxicated when in fact the patient has a subdural hematoma. In these circumstances, the BAC is much lower than expected.
  • A patient with visual hallucinations may have intra-cerebral pathology, psychotic illness or alcohol withdrawal.
  • A patient who uses cocaine and is experiencing weight loss may have underlying cancer.

Other questions about organic versus psychiatric etiology

  • Can a drug cause the signs and symptoms this patient is exhibiting?
  • Can the signs and symptoms be attributed to withdrawal from a substance?
  • Does the history of the amount consumed fit with the clinical presentation?

Determining the patient's motivation for change

Counselling a patient who is using substances about treatment options is not a good use of a primary care provider's time if the patient is not ready to change. The clinician should match the intervention to the patient's stage of change (see Table 6.1: Matching interventions to stage of change). Assessing the patient's motivation involves three components:

Assess importance

Ask the patient:

  • "Given everything else going on in your life right now, how important is it for you to stop drinking/smoking/using drugs? Use a 10-point scale where 1 is ‘not at all important' and 10 is ‘the most important thing in life.'"

Assess confidence

Ask the patient:

  • "How confident are you that you will be successful in your attempt to quit/cut down, on a scale of 1 to 10?"

Assess readiness

Finally, ask the patient:

  • "How ready are you, on a scale of 1 to 10, to take steps toward changing your behaviour?"

Patients who rate high importance, confidence and readiness are more likely to succeed in changing their substance use. Assessing these variables allows the clinician to target motivational interventions to the variables that the patient rates low. Exploring risks and rewards of substance use can create discrepancy and increase the patient's readiness to change.

Follow any of the questions with: "What would increase your importance, confidence or readiness just a little bit, from 6 to 7, for example?" This strategy can identify potential targets for intervention.

Psychiatric interviewing series

David Goldbloom and Nancy McNaughton demonstrate clinical interviewing situations.

Psychiatry in primary care toolkit

The Psychiatry in Primary Care App has been decommissioned. 

The revised print version of Psychiatry in Primary Care is avaible through the CAMH store. 

We have posted a number of revised chapters from the book in Treating Conditions and Disorders in the new Professionals section of