Understanding Medicinal Cannabis Oil How Cannabis Oil Works, Potential Benefits, Risks and Safe Use

Introduction

Medicinal cannabis is increasingly used as a treatment option for selected chronic medical conditions. Many patients ask whether cannabis oil may help with chronic pain, anxiety, insomnia or symptoms occurring around menopause.

This leaflet explains how medicinal cannabis works, the differences between cannabidiol (CBD) and tetrahydrocannabinol (THC), the conditions it may help, possible side effects, effects on the brain and mental health, and what to expect if it is prescribed.

Medicinal cannabis should always be prescribed as part of an individual treatment plan after discussing the possible benefits, limitations and risks with your healthcare professional.

What is medicinal cannabis?

Medicinal cannabis refers to medicines derived from the cannabis plant that contain one or more cannabinoids.

Unlike cannabis obtained for recreational use, legally prescribed medicinal cannabis is supplied through a pharmacy and contains specified amounts of its active ingredients. However, many medicinal cannabis products available in Australia are unapproved therapeutic goods, meaning that they have not undergone the same full assessment of quality, safety and effectiveness as medicines registered on the Australian Register of Therapeutic Goods.

Cannabis contains more than 100 naturally occurring chemicals called cannabinoids. The two best known are:

• Cannabidiol (CBD)

• Delta-9-tetrahydrocannabinol (THC)

Different cannabis oils contain different amounts and ratios of CBD and THC.

Understanding the body’s endocannabinoid system

The body naturally produces cannabis-like substances called endocannabinoids.

Together with their receptors and the enzymes that make and break them down, these substances form the endocannabinoid system, or ECS.

The ECS is involved in regulating several body functions, including:

• Sleep

• Pain perception

• Mood

• Stress responses

• Memory

• Appetite

• Nausea

• Inflammation

• Immune activity

The ECS can be thought of as one of the body’s internal signalling and balancing systems.

How does cannabis oil work?

Medicinal cannabis influences the endocannabinoid system and several other signalling systems in the brain and body.

There are two main cannabinoid receptors.

CB1 receptors

CB1 receptors are found mainly in the:

• Brain

• Spinal cord

• Central nervous system

They help influence:

• Pain perception

• Memory

• Mood

• Sleep

• Movement

• Appetite

• Nausea

THC produces many of its effects by activating CB1 receptors. This is also why THC can cause intoxication, altered perception, impaired concentration and memory problems.

CB2 receptors

CB2 receptors are found mainly in:

• Immune cells

• Peripheral nerves

• The gastrointestinal tract

• Skin

• Other body tissues

They are involved in:

• Immune regulation

• Inflammation

• Pain signalling

CBD works differently from THC. It has only limited direct activity at CB1 and CB2 receptors and influences several other receptor and signalling systems. Its effects are complex and are still being studied.

CBD and THC: What is the difference?

CBD — cannabidiol

CBD does not usually produce intoxication or a “high”.

CBD is used or investigated for conditions including:

• Certain severe forms of epilepsy

• Chronic pain

• Anxiety symptoms

• Sleep disturbance

• Some inflammatory and neurological conditions

The strongest established evidence for CBD is for particular severe epilepsy syndromes. Evidence for pain, anxiety and sleep remains variable, and CBD should not be described as proven treatment for every condition in which it is prescribed.

CBD may still cause side effects and can interact with other medicines.

THC — tetrahydrocannabinol

THC is the main intoxicating component of cannabis.

It may help some patients with:

• Chronic or neuropathic pain

• Multiple sclerosis-related muscle spasticity

• Chemotherapy-related nausea and vomiting

• Appetite loss

• Sleep disturbance associated with pain or illness

• Palliative-care symptoms

THC can also cause:

• Drowsiness

• Dizziness

• Poor concentration

• Slower reaction time

• Short-term memory impairment

• Anxiety or panic

• Paranoia

• Confusion

• Hallucinations or psychotic symptoms, particularly at higher doses

• Increased heart rate

• Poor balance

THC is generally prescribed according to the principle:

Start low, increase slowly and review regularly.

Why are some products mostly CBD while others contain THC?

The choice of product depends on the condition being treated, the patient’s medical history, the need to avoid intoxication and the balance between potential benefit and risk.

CBD-dominant oils

These may be considered for:

• Daytime treatment

• Patients wishing to avoid intoxication

• Certain epilepsy syndromes

• Selected patients with anxiety, pain or sleep symptoms

CBD-dominant does not always mean completely THC-free. Patients should check the product information carefully, particularly where driving or workplace drug testing is relevant.

Balanced CBD–THC oils

These contain both CBD and THC and may be considered for selected patients with:

• Chronic pain

• Neuropathic pain

• Multiple sclerosis-related symptoms

• Sleep disturbance associated with chronic pain

THC-dominant oils

These may be considered for selected patients with:

• Severe chronic or neuropathic pain

• Cancer-related symptoms

• Palliative-care symptoms

• Chemotherapy-related nausea and vomiting

• Severe appetite loss

THC-dominant products require closer monitoring because they are more likely to cause intoxication, cognitive impairment, anxiety and other neuropsychiatric effects.

What conditions may medicinal cannabis help?

Evidence supporting medicinal cannabis varies considerably between conditions.

The best-supported uses include selected cases of:

• Certain severe childhood epilepsies

• Chemotherapy-induced nausea and vomiting

• Multiple sclerosis-related spasticity

• Chronic neuropathic pain

• Palliative-care symptoms

Evidence is less certain or inconsistent for:

• Fibromyalgia

• Chronic musculoskeletal pain

• Anxiety disorders

• Post-traumatic stress disorder

• Primary insomnia

• Endometriosis

• Migraine

• Menopausal symptoms

Medicinal cannabis is generally considered after standard evidence-based treatments have been tried, are unsuitable or have caused unacceptable side effects.

Can cannabis oil help menopause?

Medicinal cannabis is not hormone replacement therapy and does not replace oestrogen.

It has not been shown to correct oestrogen deficiency or provide the established benefits of HRT for symptoms such as hot flushes, night sweats, vaginal dryness or bone protection.

Some women may report improvement in associated symptoms such as:

• Chronic pain

• Sleep disturbance

• Anxiety

• Night-time discomfort

However, there is currently insufficient evidence to recommend medicinal cannabis as a primary treatment for menopause.

Women experiencing menopausal symptoms should first discuss whether evidence-based HRT or other established treatments are appropriate.

How quickly does cannabis oil work?

The onset and duration of effect depend on:

• The product

• The dose

• Whether it is swallowed or held under the tongue

• Whether it is taken with food

• The individual patient’s metabolism

• Previous exposure to cannabinoids

When an oil is held under the tongue and then swallowed, effects may begin within approximately:

30–90 minutes

The strongest effects may occur after:

2–4 hours

Effects may last for:

6–12 hours

These times are approximate. Oral cannabis can have a delayed and unpredictable onset, so patients should not take additional doses too quickly.

Why is the dose increased slowly?

People vary greatly in their response to medicinal cannabis, particularly THC.

Increasing the dose slowly can reduce the risk of:

• Dizziness

• Excessive drowsiness

• Anxiety

• Confusion

• Falls

• Impaired coordination

• Unpleasant intoxication

The aim is not to reach the highest possible dose. It is to find the lowest dose that provides meaningful benefit without unacceptable side effects.

Possible side effects

CBD may cause:

• Dry mouth

• Sleepiness

• Fatigue

• Diarrhoea

• Nausea

• Reduced appetite

• Changes in liver enzymes

• Medication interactions

THC may cause:

• Drowsiness

• Dizziness

• Dry mouth

• Poor concentration

• Slower reaction time

• Short-term memory problems

• Anxiety or panic

• Increased heart rate

• Impaired balance

• Confusion

• Paranoia

• Hallucinations or psychosis

Higher doses of THC increase the likelihood of adverse effects.

Seek urgent medical advice if you develop severe confusion, hallucinations, extreme agitation, suicidal thoughts, chest pain, fainting or symptoms of an allergic reaction.

Can medicinal cannabis become addictive?

CBD does not appear to have the same dependence potential as THC.

THC-containing products can lead to:

• Tolerance

• Dependence

• Cannabis-use disorder

• Withdrawal symptoms after regular use is stopped

Possible withdrawal symptoms include:

• Irritability

• Anxiety

• Poor sleep

• Reduced appetite

• Restlessness

• Low mood

The risk is greater with high doses, frequent use and prolonged treatment.

Medical prescribing and monitoring may reduce the risk compared with uncontrolled recreational use, but it does not eliminate it.

Can I drive?

Driving laws vary between Australian states and territories.

THC can impair concentration, coordination, judgement and reaction time. It may also be detected after the noticeable effects have worn off.

The Therapeutic Goods Administration advises patients not to drive or operate machinery while being treated with medicinal cannabis. State and territory drug-driving laws may apply even where THC has been legally prescribed.

CBD-only products are not intoxicating, but some products described as CBD-dominant may still contain small amounts of THC. CBD can also cause drowsiness in some people.

Before driving, confirm:

• Whether your product contains any THC

• Whether it makes you drowsy or cognitively impaired

• The laws that apply in your state or territory

• Your prescribing doctor’s advice

Never drive or operate machinery while impaired.

Can cannabis interact with other medicines?

Yes.

CBD and THC can alter the effects or blood levels of other medicines. Sedating effects may also be increased when cannabis is combined with alcohol or medicines that cause drowsiness.

Potential interactions include:

• Blood thinners

• Sedatives

• Sleeping tablets

• Opioids

• Benzodiazepines

• Some antidepressants

• Antipsychotic medicines

• Anti-epileptic medicines

• Some heart medicines

• Medicines metabolised by the liver

Patients taking high-dose CBD or medicines that affect the liver may require monitoring of liver function.

Always tell your doctor and pharmacist about all prescribed medicines, over-the-counter products, herbal preparations and supplements you use.

Does medicinal cannabis cause the same brain harm as smoking recreational cannabis?

Not necessarily, but medicinal cannabis is not risk-free, particularly when it contains THC.

Smoking recreational cannabis adds the harmful effects of inhaling smoke, including exposure to irritants and combustion products. Recreational cannabis may also:

• Contain an unknown or very high concentration of THC

• Contain contaminants

• Be used in larger amounts

• Be used daily or repeatedly

• Be started during adolescence

• Be taken without medical screening or supervision

Prescribed cannabis oil avoids smoke inhalation and provides a known cannabinoid concentration. It is usually started at a low dose and monitored clinically.

However, the brain does not distinguish between “medical THC” and “recreational THC”. THC can still affect memory, concentration, reaction time, anxiety and perception regardless of why it is taken.

The main differences are the dose, potency, frequency, age of exposure, route of administration, product quality and degree of medical monitoring.

Can medicinal cannabis increase the risk of psychosis or schizophrenia?

THC can cause short-term psychotic symptoms in some people, including:

• Paranoia

• Hallucinations

• Delusional thinking

• Severe confusion

Frequent use of high-potency cannabis is associated with a higher risk of developing a psychotic disorder. The association is strongest with daily or near-daily use and products containing high concentrations of THC.

Cannabis does not cause schizophrenia in every person who uses it. The evidence suggests that THC may precipitate psychosis or contribute to the development of illness in people who are already vulnerable.

The risk is higher in people who:

• Begin using cannabis during adolescence

• Use cannabis daily or almost daily

• Use high-potency THC products

• Have previously experienced psychosis

• Have schizophrenia or schizoaffective disorder

• Have bipolar disorder with psychotic features

• Have a first-degree relative with schizophrenia or another psychotic disorder

• Use other psychoactive substances

THC-containing medicinal cannabis is generally avoided in people with a personal history of psychosis and requires extreme caution where there is a strong family history of psychotic illness.

Does CBD carry the same risk?

CBD is not intoxicating and has not been associated with the same psychosis risk as THC.

CBD may moderate some effects of THC in certain settings, but it should not be assumed that CBD will reliably protect a person from THC-related anxiety, paranoia or psychosis.

CBD is being investigated for possible antipsychotic effects. However, it is not an established replacement for standard treatment for schizophrenia or another psychotic disorder.

CBD products can still cause side effects, interact with medicines and contain small amounts of THC depending on the formulation.

Can medicinal cannabis affect memory and concentration?

THC can temporarily impair:

• Short-term memory

• Attention

• Concentration

• Decision-making

• Coordination

• Reaction time

These effects are usually dose-related and may be more noticeable when treatment is started or the dose is increased.

Long-term, heavy recreational cannabis use has been associated with cognitive impairment, particularly when use begins during adolescence.

There is less evidence about the long-term cognitive effects of carefully prescribed, low-dose medicinal cannabis in adults. It should therefore not be stated that prescribed cannabis oil is harmless to the brain. The risk is likely influenced by the amount of THC, frequency and duration of treatment, age, other medicines and individual vulnerability.

Patients should report persistent memory problems, personality changes, worsening anxiety, paranoia, hallucinations or unusual behaviour promptly.

Who should avoid medicinal cannabis?

Medicinal cannabis may not be suitable, or may require specialist assessment, in people with:

• Pregnancy

• Breastfeeding

• Previous psychosis

• Schizophrenia or schizoaffective disorder

• Uncontrolled bipolar disorder

• A strong family history of psychotic illness, particularly when THC is being considered

• Active suicidal thoughts

• Active substance-use disorder

• Severe liver disease

• Significant cardiovascular disease

• Certain heart-rhythm disorders

• A history of severe adverse reactions to cannabis

A CBD-only or CBD-dominant product may sometimes be considered where THC is unsuitable, but this decision still requires careful medical assessment.

Practical tips

• Take the medicine exactly as prescribed.

• Confirm the concentration of the product before measuring a dose.

• Shake the bottle if instructed.

• Use the supplied measuring syringe.

• Hold the oil under the tongue only if directed.

• Do not take an extra dose because the effect has not started immediately.

• Avoid alcohol when beginning treatment.

• Avoid combining cannabis with sedating medicines unless your prescriber has approved this.

• Do not increase or reduce the dose without medical advice.

• Do not share the medicine with another person.

• Keep a diary of the dose, symptoms, benefits and side effects.

• Store it securely away from children and animals.

• Attend regular reviews to determine whether treatment is providing meaningful benefit.

Frequently asked questions

Will I become “high”?

CBD does not usually cause intoxication.

THC may cause intoxication depending on the dose, individual sensitivity and product formulation.

Feeling heavily intoxicated is not the goal of medicinal treatment. Contact your prescriber if you experience an unpleasant “high”, severe drowsiness, confusion, panic or paranoia.

Is medicinal cannabis the same as smoking cannabis?

No.

Medicinal cannabis products have stated concentrations of CBD and THC and are supplied through legal prescribing pathways.

Cannabis oil avoids the respiratory harms associated with inhaling cannabis smoke. However, an oil containing THC can still produce intoxication, cognitive impairment, dependence and psychiatric side effects.

Smoking cannabis is not recommended as a medical treatment.

Will I need to take it forever?

Not necessarily.

Some patients use medicinal cannabis for a limited period, while others may continue it longer term.

Treatment should be reviewed regularly and continued only when it produces meaningful improvements in symptoms or function that outweigh its risks, side effects and costs.

How will we know whether it is working?

Before treatment begins, it is helpful to identify specific goals, such as:

• Reduced pain

• Fewer night-time awakenings

• Improved daily function

• Reduced nausea

• Less reliance on another medicine

Treatment should be reconsidered if these goals are not achieved after an appropriate monitored trial.

Dr Purity’s Clinical Perspective

Medicinal cannabis is not a miracle cure, nor is it simply “natural medicine”. Like every prescription medicine, it has potential benefits, limitations, interactions and adverse effects.

One of the biggest misconceptions is that all cannabis products carry identical risks. They do not.

Smoking large amounts of high-potency recreational cannabis, particularly from adolescence, is very different from taking a measured cannabis oil under medical supervision. Smoking adds respiratory harm, while unregulated recreational cannabis may contain unknown concentrations of THC or contaminants and may be used in patterns that increase the risk of dependence, cognitive impairment and psychiatric complications.

However, prescribed THC remains THC. It can still impair memory, concentration, driving and judgement, and it can cause anxiety, paranoia or psychosis in susceptible people. The fact that a product has been prescribed does not make these effects impossible.

Medicinal cannabis should therefore be approached like any other prescription medicine. The right patient, the right product, the right dose, clear treatment goals and regular review are essential.

Where clinically appropriate, a CBD-dominant product may be considered because it does not cause the same intoxication as THC. If THC is required, I follow the principle of “start low, go slow and review regularly.” The aim is to use the lowest effective dose while monitoring closely for cognitive, psychiatric and physical side effects.

Patients with previous psychosis or schizophrenia generally should not use THC-containing products. A strong family history of psychotic illness also requires careful consideration.

For appropriately selected patients, medicinal cannabis may improve symptoms and quality of life when established treatments have been ineffective, unsuitable or poorly tolerated. It should be continued only when there is a clear, meaningful benefit that outweighs the risks.

For menopausal women, medicinal cannabis does not replace evidence-based HRT when HRT is appropriate. It may occasionally have an adjunctive role for an associated problem such as chronic pain or persistent sleep disturbance, but it is not a treatment for the underlying oestrogen deficiency of menopause.

Dr Purity’s Key Messages

• Medicinal cannabis acts on the body’s endocannabinoid and other signalling systems.

• CBD and THC have different effects and different risk profiles.

• CBD does not usually produce a “high”.

• THC may help selected symptoms but can impair memory, concentration, coordination and driving.

• THC can cause anxiety, paranoia or psychosis, particularly in susceptible people.

• Prescribed THC is not harmless simply because it is medicinal.

• Cannabis oil avoids smoke inhalation but does not remove the neurological risks of THC.

• Patients with previous psychosis or schizophrenia should generally avoid THC-containing products.

• Treatment should begin at a low dose and be increased slowly.

• Clear treatment goals and regular medical review are essential.

• Medicinal cannabis should be continued only when meaningful benefits outweigh the risks.

• Medicinal cannabis is not a replacement for HRT in menopausal women.

References

1. Therapeutic Goods Administration. Medicinal Cannabis Hub. Australian Government. Updated February 2025.

2. Therapeutic Goods Administration. Guidance for the use of medicinal cannabis in Australia: Patient information. Australian Government. Updated November 2024.

3. Therapeutic Goods Administration. Medicinal cannabis information for patients. Australian Government. Updated June 2025.

4. Therapeutic Goods Administration. Guidance for the use of medicinal cannabis in Australia: Overview. Australian Government. Updated February 2025.

5. Arnold JC, Nation T, McGregor IS. A primer on medicinal cannabis safety and potential adverse effects. Australian Journal of General Practice. 2021;50(6):345–350.

6. National Academies of Sciences, Engineering, and Medicine. The Health Effects of Cannabis and Cannabinoids: The Current State of Evidence and Recommendations for Research. Washington, DC: National Academies Press; 2017.

7. MacCallum CA, Russo EB. Practical considerations in medical cannabis administration and dosing. European Journal of Internal Medicine. 2018;49:12–19.

8. Whiting PF, Wolff RF, Deshpande S, et al. Cannabinoids for medical use: A systematic review and meta-analysis. JAMA. 2015;313(24):2456–2473.

9. Häuser W, Petzke F, Fitzcharles MA. Efficacy, tolerability and safety of cannabis-based medicines for chronic pain management: An overview of systematic reviews. European Journal of Pain. 2018;22(3):455–470.

10. Di Forti M, Quattrone D, Freeman TP, et al. The contribution of cannabis use to variation in the incidence of psychotic disorder across Europe: The EU-GEI multicentre case-control study. The Lancet Psychiatry. 2019;6(5):427–436.

11. Di Forti M, Morgan C, Dazzan P, et al. High-potency cannabis and the risk of psychosis. British Journal of Psychiatry. 2009;195(6):488–491.

12. Murray RM, Englund A, Abi-Dargham A, et al. Cannabis-associated psychosis: Neural substrate and clinical impact. Neuropharmacology. 2017;124:89–104.

13. World Health Organization Expert Committee on Drug Dependence. Cannabidiol (CBD): Critical Review Report. Geneva: World Health Organization; 2018.

14. Fischer B, Russell C, Sabioni P, et al. Lower-Risk Cannabis Use Guidelines: A comprehensive update of evidence and recommendations. American Journal of Public Health. 2017;107(8):e1–e12.

15. Royal Australian College of General Practitioners. Cannabis use and its associated disorders: Clinical care. Australian Family Physician. 2016;45(12):877–880.

Important Information

This leaflet provides general educational information only and does not replace personalised medical advice.

Medicinal cannabis should only be commenced, adjusted or discontinued under the supervision of an appropriately qualified healthcare professional. Always discuss the possible benefits, limitations, side effects, medication interactions, mental-health risks and driving restrictions with your prescribing clinician.

Dr Purity Carr | GP | Menopause Doctor

Purity Health Menopause & Wellbeing Centre