Starting CBD in Australia usually means a low first dose, raised in steps over several weeks, with your prescriber checking for side effects along the way. The most common early effects are sleepiness, reduced appetite and diarrhoea.1 CBD is not intoxicating, so the first weeks are mostly about watching, recording and reviewing.
What should happen before the first dose?
A careful start involves a few checks. These are worth raising if your prescriber does not.
- Your full medicine list. CBD slows several of the liver enzymes that clear other medicines, and is itself cleared by two of them.1 A systematic review rated warfarin, valproate, tacrolimus and sirolimus as the most widely reported and potentially highest-risk interactions.2 Include over-the-counter and herbal products. See CBD drug interactions.
- Liver blood tests. For the registered CBD epilepsy medicine, the US prescribing information calls for liver tests before starting, at 1, 3 and 6 months, and then periodically.1 Whether you need them at your dose is your prescriber’s call. See CBD and the liver.
- Pregnancy and breastfeeding. TGA patient guidance says medicinal cannabis is not appropriate for women who are pregnant, planning a pregnancy or breastfeeding.3 See CBD in pregnancy and breastfeeding.
- What you are trying to change. For several common uses, including chronic pain and arthritis, controlled trials found CBD no better than placebo (a dummy treatment).4 Check how we grade the evidence and the page for your condition, and agree with your prescriber on how you will judge success.
See also who should not take CBD.
How is the dose built up?
By titration: start low, then step up. For the registered CBD medicine in two severe childhood epilepsies, the US prescribing information starts at 5 mg per kilogram of body weight per day, split into two doses, and increases after one week.1 Australian prescribing information may differ.
For other conditions there is no standard schedule, because nearly all CBD products prescribed in Australia are unapproved medicines without an official dose chart.5 Your prescriber decides the starting dose, the size of each step and the gap between steps. The CBD dosage guide shows what trials used, and the dose calculator converts a prescribed dose in milligrams to millilitres of your oil.
What side effects are common in the first weeks?
The best numbers come from epilepsy trials, where doses were high (10 to 20 mg per kilogram per day) and most participants were also taking other anti-seizure medicines. In those trials:1
- sleepiness or sedation affected 32% of people on CBD and 11% on placebo
- among people also taking clobazam (an anti-seizure medicine), the figure was 46%, against 16% in those not taking it
- liver enzymes rose above three times the normal limit in 13% on CBD and 1% on placebo.
Other sources fill in the picture for other groups.
| Source | Who | What it found |
|---|---|---|
| Meta-analysis of randomised trials, 20206 | People in CBD trials across conditions | CBD was linked to diarrhoea and sleepiness. After childhood epilepsy studies were excluded, diarrhoea was the only side effect linked to CBD |
| Review of oral CBD trials, 2020 to 20227 | Trial participants across conditions | Most side effects were mild or moderate: gut symptoms 59.5%, sleepiness 16.7%, loss of appetite 16.5%, raised liver enzymes 12.8% |
| Australian insomnia trial8 | 30 adults taking 150 mg a night for 2 weeks | No impairment of thinking the next day. Dry mouth was more common with CBD |
| TGA patient information (covers CBD and THC products)3 | People prescribed medicinal cannabis | Lists fatigue, sedation, vertigo, nausea, vomiting, fever, appetite change, dry mouth and diarrhoea |
The World Health Organization’s review judged CBD “generally well tolerated with a good safety profile” and noted that some reported side effects may come from interactions with a person’s existing medicines.9
Liver enzyme rises usually cause no symptoms, which is why they are picked up by blood tests and not by how you feel. In a US Food and Drug Administration study, 5.6% of healthy adults taking about 350 to 400 mg a day had significant rises within 28 days. None had symptoms, and levels returned to normal within 1 to 2 weeks of stopping.10
Full details are on CBD side effects.
Will you feel anything?
CBD does not cause a high. In an Australian study of 17 adults, single oral doses of 15, 300 or 1,500 mg did not impair thinking or cause feelings of intoxication.11 See does CBD get you high?
That has a practical side. With no obvious sensation, the only way to tell whether anything has changed is to compare your symptoms before and after. A short daily note of the symptom you care about, started a week or two before the first dose, gives you and your prescriber something firmer than memory.
When might you notice a change?
It depends on the condition, and for some there may be no change. In epilepsy trials, seizure rates separated from placebo within the first 1 to 2 weeks.12 Trials in other conditions usually ran for 2 to 12 weeks. See how long does CBD take to work?
Does it matter how you take it?
Yes. A high-fat meal raised total exposure to swallowed CBD about 4-fold compared with an empty stomach. The prescribing information says to take it consistently, either always with food or always without.1 Pick the routine your prescriber advises and stick to it. See taking CBD with food.
Alcohol raises CBD blood levels and adds to sleepiness.1 See CBD and alcohol.
Can you drive?
Studies of pure CBD have found little impairment, but they were small. The Australian study above found no impairment of thinking at doses up to 1,500 mg, with some driving comparisons inconclusive.11 Two cautions apply.
- CBD can make you sleepy, more so with clobazam, alcohol or other sedating medicines.1
- If your product contains any THC, the position is different. TGA guidance on medicinal cannabis, written with THC in mind, says patients should be advised they are not able to drive while being treated.13
See CBD and driving in Australia before you get behind the wheel.
When should you contact your prescriber?
Your prescriber or pharmacist should tell you which symptoms to report for your product and dose. As a general guide, get in touch if:
- sleepiness is affecting your day or your safety
- diarrhoea or loss of appetite does not settle (the Australian product information for Epidyolex lists diarrhoea and sleepiness among the effects of taking too much)14
- you start, stop or change any other medicine
- you become pregnant or plan to
- you want to stop. People taking CBD for epilepsy should not stop suddenly, because seizures can increase.1 See stopping CBD.
When is it time to review?
Set a review date at the first appointment. TGA guidance says treatment should be stopped if benefit has not been demonstrated.13 A review is also the time to ask whether the dose, the product or the cost still makes sense. See how much CBD costs in Australia.
Footnotes
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US National Library of Medicine, DailyMed. Epidiolex (cannabidiol) oral solution: prescribing information, revised 2026. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=8bf27097-4870-43fb-94f0-f3d0871d1eec ↩ ↩2 ↩3 ↩4 ↩5 ↩6 ↩7 ↩8 ↩9
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Systematic review of drug interactions with cannabidiol and other cannabinoids. https://pmc.ncbi.nlm.nih.gov/articles/PMC11167383/ ↩
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Therapeutic Goods Administration. Guidance for the use of medicinal cannabis in Australia: patient information. https://www.tga.gov.au/sites/default/files/guidance-use-medicinal-cannabis-australia-patient-information.pdf ↩ ↩2
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Moore RA, Straube S, Fisher E, Eccleston C. Cannabidiol (CBD) products for pain: ineffective, expensive, and with potential harms. Journal of Pain, 2024. https://doi.org/10.1016/j.jpain.2023.10.009 ↩
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NPS MedicineWise. Medicinal cannabis: what you need to know. https://www.nps.org.au/professionals/medicinal-cannabis-what-you-need-to-know ↩
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Chesney E, et al. Adverse effects of cannabidiol: a systematic review and meta-analysis of randomized clinical trials, 2020. https://pubmed.ncbi.nlm.nih.gov/32268347/ ↩
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Review of adverse events in randomised trials of oral cannabidiol, 2020 to 2022 (journal article). https://pmc.ncbi.nlm.nih.gov/articles/PMC9782576/ ↩
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Cognition and next-day function results from the Australian trial of 150 mg nightly cannabidiol for insomnia (journal article). https://pmc.ncbi.nlm.nih.gov/articles/PMC11063694/ ↩
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World Health Organization, Expert Committee on Drug Dependence. Cannabidiol (CBD) critical review report, 2018. https://cdn.who.int/media/docs/default-source/controlled-substances/whocbdreportmay2018-2.pdf ↩
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EurekAlert news release on Florian J, et al., JAMA Internal Medicine, 2025 (cannabidiol and liver enzyme elevations in healthy adults). https://www.eurekalert.org/news-releases/1089832 ↩
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McCartney D, et al. Effects of cannabidiol on simulated driving and cognitive performance: a dose-ranging randomised controlled trial. Journal of Psychopharmacology, 2022. https://pubmed.ncbi.nlm.nih.gov/35637624/ ↩ ↩2
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Long-term cannabidiol treatment in Lennox-Gastaut syndrome: open-label extension results. Epilepsia (copy hosted by University College London). https://discovery.ucl.ac.uk/id/eprint/10126054/1/epi.16878.pdf ↩
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Therapeutic Goods Administration. Guidance for the use of medicinal cannabis in Australia: overview. https://www.tga.gov.au/resources/resource/guidance/guidance-use-medicinal-cannabis-australia-overview ↩ ↩2
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Therapeutic Goods Administration. Australian Product Information: Epidyolex (cannabidiol) oral solution, AusPAR attachment, 2021. https://www.tga.gov.au/sites/default/files/auspar-cannabidiol-210115-pi.pdf ↩
Common questions
What does "start low, go slow" mean?
It is a common way of describing titration, which means beginning with a low dose and raising it in steps while watching for benefit and side effects. For the registered CBD epilepsy medicine, the US prescribing information starts at 5 mg per kilogram per day and increases after one week. Your prescriber sets the actual steps.
What side effects should I expect when starting CBD?
In trials of prescription doses, the most common were sleepiness, reduced appetite, diarrhoea, tiredness and raised liver enzymes on blood tests. A review of trials from 2020 to 2022 found most side effects were mild or moderate. Sleepiness is more likely if you also take clobazam, alcohol or other sedating medicines.
Will CBD make me feel high?
No. CBD is not intoxicating. In studies, single oral doses of up to 1,500 mg caused no feelings of intoxication. It can cause sleepiness, though, and products that also contain THC are a different matter.
Can I drive when I start CBD?
Small studies found pure CBD did not clearly impair driving or thinking, though some driving comparisons were inconclusive, and CBD can cause sleepiness, especially with clobazam, alcohol or other sedatives. Any product containing THC can impair driving and lead to a positive roadside test. Ask your prescriber about your specific product.
What if CBD is not working for me?
Tell your prescriber rather than raising the dose yourself. TGA guidance says treatment should be stopped if benefit has not been demonstrated. For several common uses, controlled trials found CBD no better than placebo.
This page is general information, not medical or legal advice. Laws and evidence change; we show the date we last checked the facts at the top of every page. Talk to your doctor or pharmacist before starting, stopping or changing any medicine.
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