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Cannabis (Marijuana) Use in Adults: Information for Primary Care

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Sommaire : Cannabis is the most widely used illicit drug in Canada, with a prevalence of 9% in Canadians 15-years and older. Family physicians can make a significant impact by identifying cannabis use and supporting patients who wish to reduce their use. Motivational interviewing, which focuses on building a connection rather than simply telling patients to quit, provides a powerful way to connect with even the most reluctant patients. Though some patients may be able to quit on their own, others may require formal addictions services.
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20% of patients encountered for a primary care visit have a problem with substance use (Mersy, 2003).

Clinical Presentation / Signs and Symptoms

Most patients do not present to their primary care physicians office in acute cannabis intoxication and often times the signs/symptoms of cannabis withdrawal are missed if physicians do not enquire about past cannabis use.

Red Flags

Screen patients (especially adolescents and young adults) presenting with:

  • Frequent respiratory problems unexplained by other causes
  • Anxiety disorders, depression, or other mental health problem
  • Poor performance and or increased absences from school or work


DSM-5 Cannabis Use Disorder

  • A problematic pattern of cannabis use leading to clinically significant impairment or distress, as manifested by at least two of the following, occurring within a 12-month period:
  1. Cannabis is often taken in larger amounts or over a longer period than was intended.
  2. There is a persistent desire or unsuccessful efforts to cut down or control cannabis use.
  3. A great deal of time is spent in activities necessary to obtain cannabis, use cannabis, or recover from its effects.
  4. Craving, or a strong desire or urge to use cannabis.
  5. Recurrent cannabis use resulting in a failure to fulfill major role obligations at work, school, or home.
  6. Continued cannabis use despite having persistent or recurrent social or interpersonal problems caused or exacerbated by the effects of cannabis.
  7. Important social, occupational, or recreational activities are given up or reduced because of cannabis use.
  8. Recurrent cannabis use in situations in which it is physically hazardous.
  9. Cannabis use is continued despite knowledge of having a persistent or recurrent physical or psychological problem that is likely to have been caused or exacerbated by cannabis.
  10. Tolerance, as defined by either of the following: a) A need for markedly increased amounts of cannabis to achieve intoxication or desired effect; b) Markedly diminished effect with continued use of the same amount of cannabis.
  11. Withdrawal, as manifested by either of the following: a) The characteristic withdrawal syndome for cannabis; b) Cannabis (or a closely related substance) is taken to relieve or avoid withdrawal symptoms


History/Interviewing Questions

The following screening questions are based on the DSM-5 criteria: 



  • I’m going to ask you a few questions, based on the last 12 months…
  • How much cannabis did you use in the past week or month?
  • How do you like to use cannabis?
    • Do you smoke it? (e.g. joint, blunt, bong, etc)
    • Do you eat it? (e.g. cannabis products)

Once you have determined the amount of cannabis your patient consumes and the specific forms of use with the above questions you can continue with the next set of questions below:



  • Have you increased the amount of cannabis you use?
  • Have you tried to cut down or quit your cannabis use more than once and failed?
  • Do you spend a lot of time, money and effort getting, using and recovering from cannabis?
  • Do you get a craving, or a strong urge to use cannabis?
  • Have you missed any days of work or school due to cannabis use?
  • Do you continue to use cannabis, even though it causes you problems in your relationships or  family?  
  • Do you ever miss important social, recreational or work events because of cannabis use?
  • Do you use cannabis in dangerous situations ie. while driving, operating machinery, with other drugs, etc.?
  • Do you use Cannabis even though it causes you physical and or psychological problems?
  • Over the past 12 months have you needed more cannabis to get the same high?
  • Are you getting less high with the same amount of cannabis?
  • Do you smoke cannabis to get rid of your withdrawal symptoms?

As per DSM-5 criteria, if your patient answers yes to 2 or more of the above questions they may have a cannabis use disorder.

Physical Exam

Physical exams on otherwise healthy cannabis users are usually normal.



Tachycardia may indicate acute intoxication or an anxiety disorder (Hall, 2009).

General observations

Strong odors may indicate daily or recent cannabis use. 

Excessive colognes or perfumes may indicate an attempt to mask the smells of cannabis use.

Head and Neck

Conjunctival injection may indicate recent cannabis use (NIDA, 2012).

Oral cavity (i.e. mouth, lips and tongue) may show dry mucous membranes; tar or resin stains on the lips or tongue particularly in patients who smoke blunts (rolled cigar papers) or joints without using a filter.


Do respiratory and cardiovascular exam as you would in a tobacco smoker.

Mental status exam


Any problems with mood / affect?

Thought content

Any delusions such as paranoid ideation?


Any visual or auditory hallucinations?


Investigations are usually not needed or recommended in the primary care setting; most patients that are seeking help will self report their cannabis use (NCPIC, 2013).

Urine testing

  • Urine toxicology testing using the Enzyme Multiplied Immunoassay Technique (EMIT) urine test is the most widely used test for cannabis use detection (NCPIC, 2013).
  • Urine toxicology is best used as an adjunct to patients self reported cannabis use (NCPIC, 2013).
  • Urine toxicology can also help to rule out suspected poly drug use, as it can detect recent amphetamine, benzodiazepine, cocaine, and opioid use. 

Are you concerned about  possible respiratory problems in long term smokers?

  • Order chest XR or pulmonary function testing (PFT) including spirometer to assess lung function and rule out obstructive lung disease.

Treatments for Cannabis Use Disorder

Medication treatment

  • Currently there are no approved medications for treatment of cannabis use disorder in Canada.


  • Cognitive Behavioural Therapy (CBT)
  • Motivational Interviewing (MI)

Motivational Interviewing Guide

When faced with a patient with negative behaviours, physicians (as well as the patient’s well meaning loved ones) generally respond by giving advice, or telling the patient what to do.

Unfortunately, the patient may then feel non-validated, which then leads to the patient becoming defensive, which then leads to reinforcement of the negative behavior.

Motivational interviewing takes a different approach: 

  • The focus is on accepting, validating and empathizing with the patient
  • By doing so, the patient feels understood and empathized with
  • Patients who feel understood are then (paradoxically) more able to think about changing the negative behavior, and embracing the more positive behaviours that the clinician would like
  • Basic assumptions with motivational interviewing
  1. Change occurs naturally
  2. Change is influenced by the interactions between people 
  3. Showing empathy towards your patient is a means of effecting change
  4. The best predictor of change is confidence, on the part of the patient or the practitioner, that the patient will change
  5. Patients who say they are motivated to change are more likely to change

Do’s in Motivational Interviewing

  • Try to find out why the patient smokes, and then empathize with the (healthy) reason
    • “Most people who smoke marijuana do so for a reason.”
    • “What makes you smoke?” “What do you get out of smoking?”
    •  “So it sounds like with all the stress you are under, marijuana is one way that helps you cope with the stress. I can’t blame you… It sounds like things are pretty stressful for you. No wonder you need to have a way to cope…”
    • “So the marijuana helps you focus and concentrate… Well, I can understand why you might want to use the marijuana. Its important to be able to focus and concentrate…”
  • Show the disadvantages of the behavior
    • “How does smoking cannabis affect you in your school, work life and family life?”
    • “How does cannabis use affect you financially?”
    • “Does your family/friends/partner mind you using cannabis?”
  • Show the benefits of change   
    •  “You’ve mentioned that finances are a stress. How much money would you save if you quit smoking?”
    • “You’ve mentioned you’ve had fights with your partner over this. How would your partner feel if you quit smoking?”
    • “You’ve mentioned that you’ve missed a lot of work from smoking marijuana. How would your work be affected if you quit smoking?”
  • Explore alternative ways to reach the same benefit
    •  “What would it be like if we could find another way to help you focus and concentrate / deal with stress / etc…?”
  • Show that change is possible (optimism for change)
    •  “I have confidence that if you want to stop smoking marijuana, that you can do this.”
    • “And there are things I can do to support you as well...”
  • Support patients in their intention to change
    • “I'm happy to see you have decided to quit smoking marijuana”
    • “I would like to see you back sooner so we stay on track”
    • “You don’t have to do this all on your own. There are services and groups that can help you to quit… Would you like to learn more?”

When to Refer

Consider referral if your patient meets any one of following criteria:

1. Signs/symptoms of marijuana intoxication may include all of the following except:
2. Cannabis use disorder can be managed in the following ways EXCEPT


  • Bashford, J. Screening and assessment for cannabis use disorder, National Cannabis Prevention and Information Centre website at:, date accessed [Dec, 16,2013]
  • Beautrais AL, Joyce PR, Mulder RT. Cannabis abuse and serious suicide attempts. Addictions 1999; 94:1155-64
  • Fergusson, D.M.; and Boden, J.M. Cannabis use and later life outcomes. Addiction 103(6):969–976; discussion 977–968, 2008

About this Document

Written by Dr. Gurpreet Dhillon, Family Medicine Resident. Reviewed by members of the Family Medicine Program at the University of Ottawa, including Dr's Farad Motamedi; Mireille St-Jean; Eric Wooltorton (2014).


Information in this pamphlet is offered ‘as is' and is meant only to provide general information that supplements, but does not replace the information from an accredited Continuing Medical Education (CME) provider. 

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Affichée le : Mar 22, 2014
Date de la dernière modification : Dec 21, 2022

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