Guest Post: Cannabis - An Overview for Pharmacists from the BC Drug and Poison Information Centre | College of Pharmacists of British Columbia

Guest Post: Cannabis – An Overview for Pharmacists from the BC Drug and Poison Information Centre

By Shelina Rayani RPh, CSPI, BC Drug and Poison Information Centre
Reviewed by C. Laird Birmingham, MD, MHSc, FRCPC and Hanif Rayani, RPh

A version of this article was originally published in BC Pharmacy Association’s Tablet in November 2018.

Pharmacists play an important role in supporting patients in making informed choices about their care. This means that pharmacists can have a role in counselling patients related to cannabis use, including drug interactions, management of side effects, potential addictive behaviours and contraindications. 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. Marijuana is derived from the flowering buds of various female cannabis species. Over one hundred unique compounds known as phytocannabinoids have been isolated from cannabis. Two of these compounds have been most studied. These are Delta-9-tetrahydrocannabinol (THC) and Cannabidiol (CBD).

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. CBD has antipsychotic, anxiolytic, antiepileptic and anti-inflammatory effects. The ratio of THC to CBD in each strain of cannabis is responsible for its therapeutic and adverse effects. Cannabis strains used recreationally for a euphoric effect contain higher levels of THC, whereas, medicinal cannabis strains have a higher CBD to THC ratio.

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.

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). 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.

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. It has no euphoric properties. Fibre from hemp stalks can be used in making paper, textiles, rope or twine, and construction materials. Grain from hemp can be used in food products, cosmetics, plastics and fuel.

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)
Drug interactions (See Table 2)
Counseling patients to label cannabis products e.g. label edibles (gummies, brownies, cookies) for safety. Pediatric ingestion can cause significant CNS depression, hypotonia and coma.
Storage as per manufacturer insert. Keep out of reach of children.
Contraindications: Pregnancy, breastfeeding, known sensitivity to cannabis.
Avoid use in those under age 25, history of psychosis, cardiovascular disease, and/or respiratory disease.
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.
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.

TABLE 1: Comparitive Of Medicinal & Recreational Cannabis

	Medicinal Cannabis	Recreational cannabis
Possession Limits	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 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
Indication	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.)
Cannabinoid Ratio	CBD>THC (less psychoactive)	THC>CBD (more psychoactive)
Types	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
Dosage Forms	Dried cannabis, extracts in oil, tinctures, concentrates, edibles, beverages, capsules
Route	Inhalation (smoking, vaporized), oral, buccal/sublingual, topical, rectal
Availability	Legal 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) Illegal Illicit source Grow own (without registration)	Legal 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 Illegal Illicit source Grow own
Pros/Cons	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

Pharmacokinetics*

Route	Bioavailability	Onset	Peak	Duration
Inhalation	15%	5 to 10 min	10 to 20 min	2 to 4h (Up to 24h)
Oral	6% to 20%	30 to 60 min (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)

Route

Bioavailability

Onset

Peak

Duration

Inhalation

15%

5 to 10 min

10 to 20 min

2 to 4h

(Up to 24h)

Oral

6% to 20%

30 to 60 min

(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.

Table 2: Cannabis Drug Interactions

THC and CBD are metabolized by CYP1A2, 2C9, 2D6, 2C19 and 3A4

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	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
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	Avoid Cannabis is sometimes used with opioid for synergy
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, Cocaines, MDMA)	Additive hypertension, tachycardia, cardiotoxicity Prolongation of stimulants' hyperthermia	Avoid
Highly protein bound drugs (e.g. Warfarin)	Potential to displace drugs that are protein bound	Monitor therapy

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.

Cannabis Legalization in Canada
Learn more about Cannabis legalization in Canada in the College’s ReadLinks article on Cannabis Legalization in Canada.

BC Drug and Poison Information Centre

The BC Drug and Poison Information Centre (DPIC) was established in 1975 through the cooperative efforts of the Hospital Programs Branch of the BC Ministry of Health and the Faculty of Pharmaceutical Sciences at the University of British Columbia (UBC). It is located at the BC Centre for Disease Control in Vancouver and is staffed with pharmacists, nurses, and physicians who have specific expertise in the provision of drug and poison information services.

The original mandate of the Centre called for the development of centralized services to assist health professionals throughout BC in providing optimal levels of drug therapy and poison management. Considerable progress has been made in this respect through expansion of DPIC programs over the ensuing years. Notably, the Centre has assumed provision of poison information services to the BC public, a population of approximately 4.4 million.

Guest Post Disclaimer

ReadLinks Guest Posts are intended to expose the public and pharmacy professionals to a diverse range of knowledge, and expertise, with the goal of expanding awareness of issues related to public safety and pharmacy practice. While the College enforces strict Guest Post Submission Guidelines, the views and opinions expressed in Guest Posts articles are those of the author(s) and do not necessarily reflect the official standards or positions of the College of Pharmacists of British Columbia.

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Guest Post: Cannabis - An Overview for Pharmacists from the BC Drug and Poison Information Centre Jan. 29, 2019 Guest Post, cannabis