The Evidence for Medicinal Cannabis

Currently, most cannabis medicines available in Australia are unregistered medicines, meaning they have not been fully assessed by the Australian Government’s Therapeutic Goods Administration (TGA) for safety and efficacy, although they are required to meet strict quality standards. As with all medicines, the potential benefits and harms need to be rigorously investigated and assessed against established treatment options.

For up to date information about the scientific evidence for the use of cannabis medicines in palliative care, nausea and vomiting, epilepsy, multiple sclerosis and pain, please see the guidance documents published on the TGA’s website.

Prescribing Medicinal Cannabis

Since 2016, the Commonwealth and State and Territory governments have undertaken a number reforms to allow for the legal prescribing of cannabis for medicinal purposes. However, further research is necessary to obtain evidence about the effectiveness and most suitable doses of medicinal cannabis products for use in different medical conditions. To enable legal access to medicinal cannabis until further research is completed, the TGA allows for registered medical practitioners to apply for access to unregistered (non-ARTG) medicinal cannabis products on a case-by-case basis via Special Access Scheme Category B (SAS-B) or the Authorised Prescriber (AP) Scheme.

The Therapeutic Goods Administration does not place any limitation on the conditions for which a healthcare practitioner can prescribe medicinal cannabis. Therefore, if the practitioner feels that medicinal cannabis products are a viable treatment option for their patients – they may prescribe appropriate unregistered medicinal cannabis products in accordance with the current regulatory framework.

The following section outlines the process for prescribing medicinal cannabis in Australia.

Providing a clinical justification

To enable an approval for access to medicinal cannabis, a clinical justification for the use of medicinal cannabis for the patient’s specific medical condition must be documented. The clinical justification should include:

1. A summary of the patient’s unmet medical need(s).
2. The clinical justification sources indicating the potential benefit of a medicinal cannabis therapy for the patient.
3. A proposed therapeutic treatment plan outlining the terms of the therapy period, including dosing strategy and monitoring and evaluation arrangements.

Selecting a suitable formula

Once you have determined there is a clinical justification for the use of medicinal cannabis, a suitable formula may be selected. Review the available information regarding medicinal cannabis formulations, routes of administration, and dose as they pertain to the patient’s unmet medical need(s).

If you require further assistance identifying a suitable formula for your patient, please contact us and a member of our medical services team will get in touch.

Dosing

There is no scientifically defined dose of medicinal cannabis for any specific medical condition. The dosage and timing of dosing will vary highly across patients and should be targeted to maximise the therapeutic benefits and minimise unwanted adverse effects.

Consistent with TGA recommendations and international guidelines, the general approach to dosing should be to “start low, go slow”. Patients should be advised that a titration period of several weeks may be required to determine the optimal dose. Although most patients will find their ideal dose in the first few days, individual circumstances may vary, and it may take longer for others to identify the optimal dose.

Initial Treatment Plan

The TGA suggests that an initial treatment plan indicate that the medicinal cannabis product be used for a one-month trial to determine the effectiveness of the medication for the patient’s condition/symptoms. The initial treatment plan should clearly indicate the treatment goals for medicinal cannabis use as well as the starting and stopping guidelines. It is recommended that these be clearly documented and discussed with the patient, related to the symptoms for which the patient is prescribed the medicinal cannabis product and, if possible, should be measurable. Examples include weight gain in patients with cachexia, cessation or minimisation of nausea and vomiting, and improved function and quality of life in patients with chronic non-cancer pain.

The initial treatment plan should also indicate:

1. The monitoring arrangements – including communication with the patient weekly, fortnightly, or monthly to establish perceptions of efficacy in symptom management, or perform any blood tests, specialist reviews, or other investigations (as needed) for the particular medical condition and/or symptoms being treated.
2. An exit strategy for situations where the medicinal cannabis product is not helping to manage the symptoms, the goals of treatment are not reached, or the patient is dissatisfied.
3. That informed consent has been obtained and the patient provided with information about the medicinal cannabis product, possible side effects and treatment goals, and that treatment will be discontinued if benefit has not been demonstrated.

In addition to the above if the product is being prescribed by a general practitioner for a pre-existing condition for which the patient is already consulting a specialist, support for the use of the medicinal cannabis formula should be sought from the consulting specialist and their acknowledgement should be documented.

Contraindications

Medicinal cannabis is contraindicated in patients:

• Who are allergic or have a hypersensitivity to cannabinoids
• Who have a personal or family history of serious psychiatric disorders (particularly schizophrenia)
• Who have unstable cardiovascular disease
• Who are pregnant, planning on becoming pregnant or are breastfeeding

Safety and Toxicity

Medicinal cannabis products are generally regarded as having low acute toxicity. However, concurrent use of other drugs may mask the effects of cannabis and severe toxicity including adverse cardiovascular effects and death may be under-recognised.

In mammals, the median lethal dose of THC has been estimated to be >800mg/kg. CBD appears to be of very low toxicity. Doses of 1000mg/kg CBD appear to have been tolerated safely in humans.