Medicinal and Recreational Cannabis


Pharmacy's role in counselling patients


With the legalization of recreational cannabis in Canada on Oct. 17, 2018, BC Drug and Poison Information Centre pharmacist Shelina Rayani explores how pharmacists can counsel patients who are on various forms of cannabis.


By Shelina Rayani RPh, CSPI, BC Drug and Poison Information Centre

Reviewed by C. Laird Birmingham, MD, MHSc, FRCPC and Hanif Rayani, RPh


When recreational cannabis becomes legalized, pharmacists will play an active role in counselling patients on appropriate use, drug interactions, management of side effects, potential addictive behaviours and contraindications.1 This article provides an overview of medicinal versus recreational cannabis, drug interactions and factors to consider when evaluating patients.


Marijuana is the common name for cannabis.2-5 Marijuana is derived from the flowering buds of various female cannabis species.2-5 Over one hundred unique compounds known as phytocannabinoids have been isolated from cannabis. Two of these compounds have been most studied.1-8 These are Delta-9-tetrahydrocannabinol (THC) and Cannabidiol (CBD).1-8

THC may have some beneficial effects as an analgesic, antiemetic, appetite stimulant and muscle relaxant, but it is also responsible for the euphoria as well as most of the adverse effects associated with cannabis.1-9  CBD has antipsychotic, anxiolytic, antiepileptic and anti-inflammatory effects.1-9 The ratio of THC to CBD in each strain of cannabis is responsible for its therapeutic and adverse effects.1-9 Cannabis strains used recreationally for a euphoric effect contain higher levels of THC, whereas, medicinal cannabis strains have a higher CBD to THC ratio.2,5,8


There are three major species of the cannabis plant, as well as hybrids of these and other species.These are Cannabis sativa (highest THC level), Cannabis indica (greater CBD than THC) and Cannabis ruderalis (least psychogenic).5  Table 1 compares medicinal and recreational cannabis. Non-cannabinoid compounds found within the plant (e.g. flavonoids, terpenoids) may enhance the therapeutic effects and/or reduce the adverse effects of phytocannabinoids; this is known as the entourage effect.8

Another variant of Cannabis sativa is Hemp. Hemp is a cultivated variety of cannabis with negligible amounts of THC (less than 0.3%) and higher levels of CBD.3,10  It has no euphoric properties. Fibre from hemp stalks can be used in making paper, textiles, rope or twine, and construction materials.3,10  Grain from hemp can be used in food products, cosmetics, plastics and fuel.3,10      








  • The lesser of a 30-day supply or 150 grams of dried marijuana or equivalent amount if in another form.
  • Formulas are available to determine how many plants can be grown based on the daily quantity of dried marijuana authorized in the registered person's medical document.
  • Up to 30 grams of dried legal cannabis or equivalent in non-dried form in public
  • Up to 4 cannabis plants per household (not per person) for personal use, from licensed seeds or seedlings
  • Share up to 30 grams of dried cannabis or equivalent with other adults


  • Spasticity from multiple sclerosis
  • Neuropathic pain
  • Chronic pain (3rd line agent)
  • Specific pediatric seizure disorders
  • Antiemetic post chemotherapy
  • Recreational use
  • 19 years and older (in B.C.)



CBD > THC (less psychoactive)

THC > CBD (more psychoactive)


  • Phytocannabinoids (No Drug Identification Number (DIN) or Natural Product Number (NPN))
  • Synthetic cannabinoids (DIN, Requires prescription):

§ Nabilone (THC analogue, oral)

§ Sativex (THC & CBD, buccal)

  • Phytocannabinoids (No DIN/NPN)
  • Illicit synthetic cannabinoids


Dried cannabis, extracts in oil, tinctures, concentrates, edibles, beverages, capsules


Inhalation (smoking, vaporized), oral, buccal/sublingual, topical, rectal



  • Require medical document from MD or Nurse practitioner
  • Order from Licensed Producer (LP) on Health Canada website; OR
  • Register self or designate with Health Canada to grow own (supplies acquired from LP); OR
  • Cannabis storefront dispensary IF licensed by Health Canada (currently majority are not)




  • Illicit source
  • Grow own (without registration)


  • Licensed Producers (LP)
  • No paperwork required
  • In B.C.: Online via BC Liquor Distribution Branch and one government-owned storefront in Kamloops open on Oct. 17, 2018 (others to follow)
  • Limited amounts of fresh or dried cannabis, seeds and oils available
  • Edibles, beverages, topical creams, suppositories, concentrates and vape juice are not yet legal



  • Illicit source
  • Grow own


  • Legal products are standardized for THC/CBD content, monitored, free of pesticides/mold/contaminants
  • Legal products will probably have a higher cost
  • Recreational cannabis easier to obtain
  • Risk of drug diversion
  • Risk of dependence and addiction
  • Safety concerns








15% to 50%

5 to 10min

10 to 20min

2 to 4h (Up to 24h)



6% to 20%

30 to 60min

(Up to 1 to 3h)

2 to 4h

(Up to >6h)

Adults: 4 to 6h

(Up to 24h)

Children: 6 to 12h

(Up to 36h)

* Inhaled bioavailability varies based on the number, depth, duration and frequency of inhalations, as well as the amount of time substance is held in the lung, and If vaporized, the temperature of the vaporizer. Oral bioavailability is reduced due to extensive first pass metabolism. Food may alter bioavailability.


Pharmacists evaluating patients should consider the following:

  • Indication i.e. medicinal versus recreational
  • Cannabis strain and THC/CBD ratio
  • Route of administration and dosage form
  • Dosing (start low and go slow when titrating)
  • Adverse effects (depending on route, ratio and dose) 2-6,8,9,11-15


Euphoria, hallucinations, mydriasis, conjunctivitis, sedation, increased appetite, dry mouth, cognitive and motor impairment, agitation, tachycardia, dizziness, postural hypotension, ataxia, anxiety**, nausea and vomiting**


Impaired brain development in youth (possibly until mid 20s), potential decline in IQ, increased risk/worsens anxiety, depression, paranoid ideation, precipitation of psychosis in susceptible patients, increased risk of schizophrenia as an adult


Cannabinoid Hyperemesis Syndrome (CHS), respiratory effects (chronic bronchitis, pneumonia), lung cancer and emphysema reported in heavy smokers***, cardiovascular effects (Myocardial Infarction, Stroke)

**  Paradoxical effect

*** Many smoke tobacco concurrently. The College of Family Physicians of Canada recommends vaporization or oral ingestion rather than smoking cannabis.8


  • Drug interactions (See Table 2)
  • Labeling e.g. label edibles (gummies, brownies, cookies) for safety. Pediatric ingestion can cause significant CNS depression, hypotonia and coma.4
  • Storage as per manufacturer insert. Keep out of reach of children.
  • Contraindications: Pregnancy, breastfeeding, known sensitivity to cannabis.8
  • Avoid use in those under age 25, history of psychosis, cardiovascular disease, and/or respiratory disease.2,3,8
  • Tolerance with heavy or frequent use.
  • Dependence i.e. withdrawal symptoms from abrupt cessation in chronic users may include anxiety, irritability, craving, dysphoria and insomnia. The dependence risk for cannabis users is 9%, and higher for those that begin use during adolescence.5,6,13
  • Addiction (Cannabis Use Disorder) is the continued use of cannabis despite harm or risky behaviour, cravings and/or impaired control over cannabis use. Especially common in those who start use as adolescents.5,6,13



THC and CBD are metabolized by CYP1A2, 2C9, 2D6, 2C19 and 3A4 3,5,8,17,18,20,21,27





Increase cannabinoid concentration

Monitor for increased clinical and adverse effects of cannabis

CYP 2C9, 2C19, 3A4 INDUCERS a


Reduced cannabinoid concentration

Monitor for reduced clinical effect of cannabis


  • Cannabis is a CYP1A2 inhibitor
  • SMOKING cannabis can induce CYP1A2

Monitor therapy for enhanced or reduced clinical effect of CYP1A2 substrates

Anticholinergic drugs

(e.g. TCAs, sedating antihistamines)

Additive hypertension and/or tachycardia

Monitor therapy


(e.g. Chlorpromazine/Thioridazine)

Marked hypotension and disorientation

Monitor therapy


Case report of a fatal stroke


CNS depressants

(e.g. Alcohol, Barbiturates, Opioids, Benzodiazepines, Hypnotics)

Additive sedation and cognitive impairment

  • Avoid
  • Cannabis is sometimes used with opioids for synergy


May enhance adverse effect profile of cannabinoids

Monitor therapy

MAOI inhibitors

Possible serotonin syndrome

Caution/monitor therapy

Nicotine (transdermal)

Tachycardia (additive), stimulant effects

Monitor therapy


(e.g. Amphetamines, Cocaine, MDMA)

  • Additive hypertension, tachycardia, cardiotoxicity
  • Prolongation of stimulants' hyperthermia


Highly protein bound drugs

(e.g. Warfarin)

Potential to displace drugs that are protein bound

Monitor therapy

  a Refer to for full list of inhibitors and inducers


DISCLAIMER: This article is not a legal document and is not a comprehensive review of cannabis. It is recommended to access other available resources for more information. In addition, for the legal indications and limitations of cannabis use, pharmacists must refer to the most current and appropriate local, provincial and federal laws and guidelines.




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15. BCCDC Health Canada Cannabis Report : 2018 June. 140 p.

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