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What Is Medical Cannabis? The Basics Explained

The range of conditions that can be managed with medical cannabis is increasing exponentially, this article aims to give a brief overview of what the basics of medical cannabis are, which illnesses it may help, and how it is prescribed.

Are you a doctor considering prescribing cannabis? or a patient suffering from a medical issue that cannabis can help manage? Would you like more information on medical cannabis? If you answered “yes” to any of these questions, read on.

a close up of a medicinal cannabis flower

What is medical cannabis?

In very simple terms, medical cannabis is prescribed specifically to alleviate the symptoms of an illness. In New Zealand, medical cannabis needs to be prescribed by a doctor for a particular condition.

The therapeutic properties of the cannabis plant come mainly from the cannabinoids naturally occurring in the plant. There are between 80 and 144 cannabinoids present in the cannabis plant- the two main cannabinoids that have been found to have therapeutic effects are tetrahydrocannabinol (THC) and cannabidiol (CBD). Many of the therapeutic effects of THC and CBD are thought to be the result of their interactions with the endocannabinoid system.

The endocannabinoid system (ECS) is a complex cell-signaling system discovered in the 1990s. As a result of this discovery, it was found that the ECS regulates multiple physiological processes involving the immune system, the nervous system, and metabolism. It also discovered cannabinoid receptors (CB1 and CB2) are scattered throughout your central and peripheral nervous system. Additionally, it found that naturally occurring cannabinoids (endocannabinoids) bind to the CB1 and CB2 receptors to exert an influence on various physiological processes. Furthermore, it was established that exogenous cannabinoids such as THC and CBD were able to bind to cannabinoid receptors in a similar way to endogenous cannabinoids.

THC is responsible for the ‘high’ often associated with cannabis due to its psychoactive properties. CBD does not create a ‘high’ and, when taken in conjunction with THC, can mitigate some of THC’s negative effects such as anxiety.

Medical cannabis can be specifically formulated to contain different ratios of THC:CBD allowing prescribers to tailor each patient’s treatment depending on their condition. This is in contrast to recreational cannabis, which is unregulated, and often contains very high levels of THC in order to maximise the ‘high’.


What conditions can medical cannabis treat?

The list of conditions that have shown benefits from medical cannabis is growing rapidly as more and more research is being published. Therefore, the following list will grow considerably as the plant is more widely studied and prescribed.

There is currently evidence for the use of medical cannabis for the following conditions:



There is ample clinical evidence for the use of medical cannabis in the management of refractory epilepsy, especially in childhood.
Multiple sclerosis (MS)
There is clinical evidence for the use of medical cannabis in the management of the pain and spasticity of MS as well as the urinary dysfunction associated with MS.
There is pre-clinical and clinical evidence to show that medical cannabis alleviates the pain associated with osteoarthritis.
Chronic pain
There is clinical evidence supporting the use of medical cannabis in the management of chronic pain (cancer and non-cancer chronic pain) as well as painful spasticity. Medical cannabis may also have opioid-sparing properties in the management of chronic pain.
Psychiatric disorders
There is clinical evidence to support the use of medical cannabis in the following psychiatric disorders: anxiety, social anxiety, insomnia, post-traumatic stress disorder, and schizophrenia (as adjunctive therapy).
Chemotherapy-induced refractory nausea and vomiting
There is clinical evidence that shows medical cannabis can decrease the symptoms of nausea and vomiting associated with chemotherapy.
Medical cannabis has been shown to assist with improving sleep quality, decreasing sleep disturbances, and decreasing sleep onset latency.
Weight gain in patients with cancer, HIV, or undergoing palliative care
Some benefit has been shown in using medical cannabis to assist with increasing appetite in patients with cancer or HIV.
In vitro and preclinical trials have shown inhibition of the growth of certain tumour cells in response to cannabinoids.
Rheumatoid arthritis (RA)
Preclinical trials have indicated a place for cannabinoids in the management of RA as a result of their anti-inflammatory properties.
Chronic pruritus (associated with contact dermatitis, atopic dermatitis, eczema, psoriasis)
Multiple pre-clinical and some preliminary clinical trials have shown medical cannabis to be effective in reducing intractable pruritus.

The range of medical conditions that respond to medicinal cannabis is likely to increase as further research takes place.

Prescribing medical cannabis

Currently, medicinal cannabis is available in New Zealand only on a doctor’s prescription. According to the BPACNZ better medicine website, as of 1 April 2020, any practitioner can now prescribe any medicinal cannabis product. These products must meet the minimum quality standards set by the Medicinal Cannabis Agency and can be prescribed for any indication within their scope of practice and where there is a clinical need.


It is important to remember the maxim ‘start low, go slow’ when initiating treatment with medical cannabis.

What to look for when prescribing medical cannabis products

The specifications surrounding the production and manufacture of medical cannabis in New Zealand stipulate that the products must comply with Good Manufacturing Practices (GMP). Therefore, these products are amongst the highest quality medicinal cannabis products available globally. This means that all registered products are extremely well-regulated. Therefore, registration of a product by Medsafe ensures that there is adequate safety and efficacy data available for the product.

There is more than just safety and efficacy to consider when prescribing medical cannabis, however.

The following also need to be considered:

  • Start low and go slow: It is important to remember the maxim ‘start low, go slow’ when initiating treatment with medical cannabis. Tolerance to THC is patient-dependent depending on a range of factors including age, metabolism, pre-existing illnesses/medications, and prior THC use. Therefore, starting at a low dose and titrating up as necessary to achieve the desired result ensures that any potential side effects are avoided or minimised.
  • Delivery method: Medical cannabis products come in various delivery methods, such as oils, sublingual sprays, capsules, creams, etc. Therefore consider what is available, which delivery methods are acceptable and which delivery methods are most efficacious for the medical condition being treated.
  • Formulation: Medical cannabis can potentially come in different ratios of THC:CBD. Ideally, one would want to be able to choose from the following: a high THC: low CBD ratio, a balanced THC:CBD ratio, and a high CBD: low THC ratio, depending on what medical condition is being treated. It is also useful to have CBD-only formulations for those patients who are wary of THC or when THC is contraindicated. The following table can give an indication of various uses of different ratios of THC:CBD:
  • Cost: Certain medical cannabis products on the market are prohibitively expensive, so check the cost before making a decision on a product.



Ratio of THC:CBD


Moderate pain, e.g. arthritis type pain


Choosing a high CBD:low THC ratio allows for pain relief without impacting functioning or mental acuity.

Severe pain, e.g. neuropathic pain and cancer pain


Severe pain responds better to either balanced THC:CBD formulations or formulations with a higher THC:lower CBD ratio. When using a higher THC component, remember the ‘start low, go slow’ principle as patients will all have a different tolerance to THC depending on age, metabolism, prior THC use etc.



Anxiety responds better to a balanced THC:CBD ratio or a higher CBD:lower THC ratio. In addition, CBD alone is also effective for the management of anxiety.

Chronic insomnia


THC has well-recognized sedating effects but can possibly increase anxiety. Adding CBD can mitigate increased anxiety. Therefore you could choose either a balanced THC:CBD formulation or a higher CBD: lower THC formulation.

Chemotherapy induced nausea and vomiting


Choose a balanced THC:CBD or higher THC:lower CBD formulation.

Spasticity (especially related to MS)


Studies were done using a balanced THC:CBD formulation (1:1 ratio).

How safe is medical cannabis?

It is reassuring to know that medical cannabis is well-tolerated and generally considered safe. Furthermore, a 2020 review of the scientific evidence for the use of THC:CBD oromucosal spray for the management of chronic pain showed no new safety concerns with long-term THC:CBD use. The review also showed no evidence of dependence. This finding supported the findings of a 2019 study that found medical cannabis, especially CBD-only formulations, to have minimal side effects.

Although medical cannabis is a very safe option for most people, there are some contra-indications to be aware of. THC and CBD are metabolised via the cytochrome P450 (CYP450) pathway. As a result, medical cannabis is contraindicated in people with disorders of CYP450 enzymes.

Medical cannabis can interact with certain medications so care should be taken when medical cannabis is prescribed with any of the following medications: warfarin, ketoconazole, clobazam, theophylline, olanzapine, and clozapine, opioids, anticholinergics, and certain antihistamines.

In summary

Patients can use medicinal cannabis for the treatment of a growing list of medical conditions. Due to that growth, this list will likely expand as more research is published. Furthermore, medical cannabis is considered safe and is generally well-tolerated with little risk of dependence.

The strict regulations in place around the registration of medical cannabis products in New Zealand should ensure that doctors feel confident when prescribing medical cannabis that they are prescribing a safe and efficacious product. You should take care when prescribing to choose the optimum delivery method and formulation specific to your patient.

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