GP considerations when prescribing medicinal cannabis

Treatment of patients with medical cannabis is increasing in regularity, but the decision to prescribe should be made with the best available information pertaining to its safety.
 
As it stands, prescribers are in an environment where patients may already be self-medicating with cannabis or are receiving inadequate benefit from their medications and wish to trial medical cannabis.
 
However, there are important safety considerations related to medical cannabis compounds, some contraindications, as well as some possible drug interactions. An understanding of the mechanism of action as it is currently understood and what cannabinoids are frequently used can help contextualise these safety considerations.
 
The major cannabinoids used therapeutically are .9- Tetrahydrocannabinol (THC) and cannabidiol (CBD), which act on the endocannabinoid system.
 
THC
The mechanism of THC is thought to be predominately due its partial agonism on CB1 and CB2 receptors found mostly in neurons and immune cells, respectively.
 
The psychoactive effects of THC are well known, but unlike opioids, THC is generally considered to have an exceptionally low toxicity, partially due to its limited involvement with brain stem areas that control respiration.
 
Nonetheless, there are some known important effects caused by THC that GPs considering a medicinal cannabis prescription should be aware of, including tachycardia, an exacerbation of psychosis, as well as unclear effects on the developing brain.
 
CBD
Unlike THC, CBD conveys no psychoactive effects. The mechanism of CBD is unclear, although recent studies have indicated that the mechanism may be complex and involve more indirect effects on the endocannabinoid system, rather than a simple interaction with CB1 and CB2 receptors.
 
The tolerability of CBD has been demonstrated to doses of 6000 mg, although costs involved with large doses would be prohibitive and such doses would be unnecessary to receive therapeutic benefit.
 
There are also a few notable potential drug interactions possible with medical cannabis, and despite no formal drug interaction studies being conducted, most medications appear safe.
 
Drug–drug interactions
Possible drug interactions may be attributed to cannabis’ involvement with CYP450 enzymes (CYP 3A4, CYP 2C9, CYP 2C19, CYP 1A1 and 1A2, as well as p-glycoprotein). Some common examples of drugs which may interact with cannabinoids include clobazam, rivaroxaban, warfarin, clopidogrel, and tacrolimus.
 
Treatment of patients with medical cannabis has reached a developing phase in Australia. Although there are many studies in the wider scientific community surrounding the safety of natural cannabinoids, it can be somewhat difficult for prescribers to apply this information to clinical practice due in part to the lack of randomised controlled trials.
 
Yet despite this, patients are being treated with cannabis at an increasing rate due to its relative safety.
 
Cannabis producer, MedReleaf Australia, has expanded its concessional access scheme to improve supply of pharmaceutical grade products for concession cardholders. Under the concession program, eligible patients will be able to access medicinal cannabis in oil and dried flower preparations, under the IndiMed brand.
 
Patients who have a Commonwealth Seniors Health Card, a Veterans Card, a Pensioner Concession Care or a Health Care Card and an active Centrelink Customer Reference Number, will be able to access the scheme.
 
Education surrounding the endocannabinoid system and medical cannabis can be provided to interested prescribers by MedReleaf Australia clinical support.
 
For more information on medical cannabis and to learn more about how to access the medication for patients, GPs can contact clinicalsupport@medreleafaustralia.com.au or register at our medical portal.
 
This content was commissioned by MedReleaf Australia.
 
Log in below to join the conversation.

medicinal cannabis MedReleaf Australia sponsored content