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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.5 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
TABLE 1: COMPARATIVE OF MEDICINAL & RECREATIONAL CANNABIS 1-9, 16-19, 22-26
|
MEDICINAL CANNABIS |
RECREATIONAL CANNABIS |
|||||
POSSESSION LIMITS |
|
|
|||||
INDICATION |
|
|
|||||
CANNABINOID RATIO
|
CBD > THC (less psychoactive) |
THC > CBD (more psychoactive) |
|||||
TYPES |
§ Nabilone (THC analogue, oral) § Sativex (THC & CBD, buccal) |
|
|||||
DOSAGE FORMS |
Dried cannabis, extracts in oil, tinctures, concentrates, edibles, beverages, capsules |
||||||
ROUTE |
Inhalation (smoking, vaporized), oral, buccal/sublingual, topical, rectal |
||||||
AVAILABILITY |
LEGAL
ILLEGAL
|
LEGAL
ILLEGAL
|
|||||
PROS/CONS |
|
||||||
PHARMACOKINETICS* |
ROUTE |
BIOAVAILABILITY |
ONSET |
PEAK |
DURATION |
||
Inhalation |
15% to 50% |
5 to 10min |
10 to 20min |
2 to 4h (Up to 24h) |
|||
Oral
|
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:
ACUTE USAGE |
Euphoria, hallucinations, mydriasis, conjunctivitis, sedation, increased appetite, dry mouth, cognitive and motor impairment, agitation, tachycardia, dizziness, postural hypotension, ataxia, anxiety**, nausea and vomiting** |
CHRONIC/HEAVY USE |
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 |
OTHER |
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
TABLE 2: CANNABIS DRUG INTERACTIONS
THC and CBD are metabolized by CYP1A2, 2C9, 2D6, 2C19 and 3A4 3,5,8,17,18,20,21,27
INTERACTING DRUG |
EFFECT |
MANAGEMENT |
CYP 2C9, 2C19, 3A4 INHIBITORS a |
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 |
CYP1A2 SUBSTRATES a |
|
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 |
Antipsychotics (e.g. Chlorpromazine/Thioridazine) |
Marked hypotension and disorientation |
Monitor therapy |
Cisplatin |
Case report of a fatal stroke |
Avoid |
CNS depressants (e.g. Alcohol, Barbiturates, Opioids, Benzodiazepines, Hypnotics) |
Additive sedation and cognitive impairment |
|
Disulfiram |
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 |
Stimulants (e.g. Amphetamines, Cocaine, MDMA) |
|
Avoid |
Highly protein bound drugs (e.g. Warfarin) |
Potential to displace drugs that are protein bound |
Monitor therapy |
a Refer to https://drug-interactions.medicine.iu.edu/Main-Table.aspx 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.
REFERENCES
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