In Australia, the use and possession of non-medicinal cannabis remain illegal in most states and territories. However, patients with specific medical conditions may be eligible for medicinal cannabis under strict regulations. The Therapeutic Goods Administration (TGA) oversees prescribing, allowing access only when conventional treatments have failed or caused intolerable side effects. To prescribe medicinal cannabis, healthcare providers must navigate regulatory pathways such as the Special Access Scheme (SAS) or obtain Authorised Prescriber status, as most cannabis-based products are not registered on the Australian Register of Therapeutic Goods (ARTG).
Cannabis Usage in Australia
Medical cannabis usage in Australia is skyrocketing.
- In 2019, there were 28,000 cannabis prescription approvals
- In 2021, there were over 70,000 SAS-B prescriptions approved
- In 2022, there were around 326,000 SAS-B prescriptions approved
Today it is estimated that roughly 2.7% of the population (of ~30 million) is using legally prescribed medicinal cannabis products¹.
Who can be prescribed cannabis in Australia?
Medicinal cannabis may be prescribed for conditions such as
- Cancer pain and/or symptoms.
- To relieve vomiting resulting from chemotherapy (a cancer treatment).
- Severe epilepsy (seizures).
- Treating muscle spasticity and pain in Multiple Sclerosis.
- Pain caused by nervous system damage.
- Palliative care – to relieve pain or symptoms related to a terminal illness.
Prescribing decisions must consider patient-specific factors, including potential contraindications like age, psychiatric disorders, cardiovascular conditions, and pregnancy. Ongoing patient monitoring, informed consent, and compliance with state and territory regulations are essential components of the prescribing process.
Online Prescribing Algorithms
Online prescribing of cannabis varies considerably among different providers. Below is a summary of the main points…
Step 1: Pre-Screen Patient Eligibility Assessment
This stage is conducted before a prescriber is consulted. It is intended to exclude high-risk and contraindicated patients. Steps within this stage include:
- Checking patient identification (KYC) and obtaining informed consent
- Confirming the patient has a diagnosed medical condition with symptoms potentially alleviated by medicinal cannabis (e.g., chronic pain, epilepsy, multiple sclerosis, chemotherapy-induced nausea).
- Screen the patient’s history of substance use and mental health conditions and conduct a mental health screening (e.g., DASS-21 or Kessler K10) if indicated.
- Ensure the patient has tried conventional therapies and found them ineffective or with intolerable side effects.
- Exclude patients with:
- Age under 25 yo.
- History or family history of psychosis, schizophrenia, or bipolar disorder.
- Current or past cannabis use disorder (CUD), those recovering from alcoholism, opioid dependence, or other drug addictions may be at a higher risk.
- Uncontrolled cardiovascular conditions (e.g., hypertension, arrhythmias, angina or a history of myocardial infarction).
- Pregnant, planning pregnancy, or breastfeeding.
- Narrow therapeutic window medication (unless blood monitoring is possible)
Step 2: Risk Assessment
Additional risk factors include:
- Taking an enzyme inducer / inhibitor / substrate
| Enzyme | Interaction and Effect | Drugs |
|---|---|---|
| CYP 3A4 |
Inducers: May decrease THC and/or CBD Inhibitors: May increase THC and/or CBD Substrates: CBD is a potential inhibitor of CYP3A4 and could increase 3A4 substrates. Caution with medications with a smaller therapeutic index (e.g., tacrolimus). Unlikely to have an effect on THC. |
Inducers: Carbamazepine, phenobarbital, phenytoin, rifampin, St. John’s wort Inhibitors: Azole antifungals, clarithromycin, diltiazem, erythromycin, grapefruit, HIV protease inhibitors, macrolides, mifepristone, verapamil Substrates: Alprazolam, atorvastatin, carbamazepine, clobazam, cyclosporine, diltiazem, HIV protease inhibitors, buprenorphine, tacrolimus, cyclosporine, phenytoin, sildenafil, simvastatin, sirolimus, verapamil, zopiclone |
| CYP 2C9 |
Inducers: May decrease THC concentration. Unlikely to have effect on CBD. Inhibitors: May increase THC concentration. Unlikely to have effect on CBD. Substrates: THC and/or CBD may increase drug levels; should monitor for toxicity. |
Inducers: Carbamazepine, rifampin Inhibitors: Amiodarone, fluconazole, fluoxetine, metronidazole, valproic acid, sulfamethoxazole Substrates: Warfarin, rosuvastatin, phenytoin |
| CYP 2C19 |
Inducers: May decrease CBD and THC. Inhibitors: May increase CBD and THC. Substrates: CBD may increase the level of medications metabolized by 2C19 such as norclobazam (active metabolite in clobazam). CBD may also prevent clopidogrel from being activated. Unlikely to have an effect on THC. |
Inducers: Carbamazepine, rifampin, St. John’s wort Inhibitors: Cimetidine, omeprazole, esomeprazole, ticlopidine, fluconazole, fluoxetine, isoniazid Substrates: Aripiprazole, citalopram, clopidogrel, diazepam, escitalopram, moclobemide, norclobazam, omeprazole, pantoprazole, sertraline |
| CYP 1A1 and 1A2 | Substrates: Smoking cannabis can stimulate these isoenzymes and increase the metabolism of these medications. | Amitriptyline, caffeine, clozapine, duloxetine, estrogens, fluvoxamine, imipramine, melatonin, mirtazapine, olanzapine, theophylline |
| p-Glycoprotein | Substrates: CBD may inhibit p-glycoprotein drug transport. Should monitor for toxicity. No effect from use of THC. | Dabigatran, digoxin, loperamide |
Double check:
- Precautions and contraindication
- Screen for interactions
- Consider the safety of the route of administration
- Consider the safety of chemovars (strain)
Step 3: Treatment Plan
- The prescriber selects a specific cannabis formulation (THC, CBD, or combination) based on symptoms and condition.
- This usually entails starting with the lowest effective dose (beginning with THC doses <10 mg) and titrating upward as needed.
Step 4: Regulatory Compliance
- The prescriber documents the consultation and discusses potential benefits, risks, and legal considerations.
Step 5: Monitoring and Review
- Schedule follow-up appointments to monitor efficacy, side effects, and adherence.
- Use validated tools to track symptom changes and side effects.
References
¹ Medical cannabis treating at least 2.7 percent of population (no date) The University of Sydney. Available at: https://www.sydney.edu.au/news-opinion/news/2022/12/16/medical-cannabis-treating-population.html (Accessed: 13 February 2025).
² MacCallum CA, Lo LA, Boivin M. “Is medical cannabis safe for my patients?” A practical review of cannabis safety considerations. European Journal of Internal Medicine. 2021;89:10-18. doi:https://doi.org/10.1016/j.ejim.2021.05.002
