CBD (cannabidiol) and THC (tetrahydrocannabinol) are both made by the cannabis plant, but they are different compounds with different effects. THC causes the cannabis high. CBD does not.1 They also differ in their risks, in what the research shows, and in how they affect driving and drug tests.
The differences at a glance
| CBD | THC | |
|---|---|---|
| Causes a high | No1 | Yes1 |
| Main action in the body | Barely binds to the CB1 receptor. Acts on many other targets, none proven to explain its effects2 | Switches on the CB1 receptor2 |
| Common side effects | Sleepiness, diarrhoea, reduced appetite, raised liver enzymes3 | Intoxication, anxiety, faster heart rate2 |
| Dependence | No case reports of abuse or dependence with pure CBD2 | Rated as “liked” far more than placebo in abuse-potential testing3 |
| Driving | Did not impair driving in two small studies, though some comparisons were inconclusive45 | Impairs driving4 |
| Drug tests | Pure CBD does not trigger a positive THC test6 | Is what the tests look for6 |
| Registered medicine in Australia | Epidyolex (CBD alone)7 | Sativex (nabiximols, a THC and CBD mix)7 |
Where do they come from?
Both come from the same species of plant. Inside the plant, both are made from the same parent compound, called CBGA. One enzyme turns CBGA into the raw form of THC and a different enzyme turns it into the raw form of CBD.2
Which one a plant makes depends on its genetics. Varieties grown as a drug have more THC than CBD in their flowers. Hemp varieties, grown for fibre and seed, make much less THC and more CBD.2 See the cannabis plant.
Why does THC cause a high and CBD does not?
THC activates a receptor called CB1, which is found mainly in the brain and nerves. In laboratory tests CBD produces no measurable response at CB1 in most studies.2
The difference shows up clearly in people. In one controlled study, healthy volunteers took 600 mg of CBD, 10 mg of THC or a placebo. THC caused intoxication and euphoria, raised heart rate and increased anxiety and psychotic symptoms. CBD did not differ from placebo on any of these measures, even though the dose was 60 times larger.2
More detail is on how CBD works and does CBD get you high?
How do the risks compare?
CBD. The main documented problems are sleepiness, diarrhoea, reduced appetite, rises in liver enzymes and interactions with other medicines.3 The World Health Organization found no case reports of abuse or dependence with pure CBD.2 See CBD side effects and CBD drug interactions.
THC. THC is intoxicating and impairs driving.4 It can cause anxiety and a faster heart rate.2 The Royal Australian and New Zealand College of Psychiatrists warns of the risk of psychosis with high-potency THC products.8 In laboratory testing, volunteers rated a pharmaceutical form of THC as far more “likeable” than placebo, while CBD at doses up to 4,500 mg stayed in the placebo range.3
Neither is suitable in pregnancy or while breastfeeding. The Therapeutic Goods Administration (TGA) says medicinal cannabis is not appropriate for women who are pregnant, planning pregnancy or breastfeeding.9
Is the medical evidence the same?
No, and this is where most confusion starts. Research on “medicinal cannabis” covers CBD alone, THC alone and mixtures. The findings do not transfer from one to another.
- Where CBD alone has strong evidence: add-on treatment of seizures in Dravet syndrome, Lennox-Gastaut syndrome and tuberous sclerosis complex, at high prescription doses.3 See CBD for epilepsy.
- Where the evidence is for products containing THC: a Cochrane review of 25 trials found that nabiximols (a THC and CBD spray) probably reduces spasticity in multiple sclerosis in the short term. That evidence is for THC-containing products, not for CBD on its own.10 See CBD for multiple sclerosis.
- Where CBD alone has been tested and not beaten placebo: in 15 of 16 randomised trials for pain, CBD did no better than placebo.11 See CBD for chronic pain.
When you read that “cannabis helps” a condition, the first question to ask is which compound was tested. Our evidence grades apply to CBD alone.
Does CBD reduce the effects of THC?
It is widely claimed that CBD softens THC. Some studies have found it reduces or opposes certain effects.2 Others have not. In a controlled study of 31 cannabis smokers, 200, 400 or 800 mg of CBD taken by mouth beforehand made no difference to the subjective effects or heart rate rise from smoked cannabis.2
A product that contains both compounds should be treated as a THC product.
What about driving?
In an on-road study of 26 people run by Australian and Dutch researchers, vaporised cannabis containing mainly CBD did not change lane weaving compared with placebo. Cannabis containing THC, with or without CBD, impaired driving 40 to 100 minutes after use. The authors cautioned that the CBD dose was low and the study was small.4 A later simulator study of 17 people found that CBD doses up to 1,500 mg did not cause feelings of intoxication or impair thinking, though some driving comparisons were inconclusive.5
Two cautions. CBD can cause sleepiness, especially with alcohol or sedating medicines.3 And any product containing THC can impair driving and lead to a positive roadside test. See CBD and driving in Australia.
What about drug tests?
Drug tests look for THC or its breakdown products, not CBD. After 100 mg of pure CBD, only 1 of 218 urine samples screened positive at the lowest cut-off and none was confirmed positive. But when the same researchers gave CBD-dominant cannabis containing a small amount of THC (3.7 mg), 2 of 6 people returned confirmed positive tests.6
The practical risk is THC in the product. Full-spectrum CBD extracts contain a little THC, and a study of patients taking one for four weeks concluded they may test positive on a urine screen.12 See Will CBD show up on a drug test? and full spectrum vs broad spectrum vs isolate.
Are they treated the same under Australian law?
Both are prescription medicines in Australia, and you need a prescription to use either lawfully.1 They are not scheduled and controlled in the same way. The details are on Schedule 3, 4 and 8: CBD scheduling explained and Is CBD legal in Australia?
Footnotes
-
healthdirect Australia. Medicinal cannabis, last reviewed February 2026. https://www.healthdirect.gov.au/medicinal-cannabis ↩ ↩2 ↩3 ↩4
-
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 ↩ ↩2 ↩3 ↩4 ↩5 ↩6 ↩7 ↩8 ↩9 ↩10 ↩11 ↩12
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Epidiolex (cannabidiol) oral solution, United States prescribing information. DailyMed, National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=8bf27097-4870-43fb-94f0-f3d0871d1eec ↩ ↩2 ↩3 ↩4 ↩5 ↩6
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Arkell TR, et al. Effect of cannabidiol and delta-9-tetrahydrocannabinol on driving performance: a randomized clinical trial. JAMA, 2020. https://doi.org/10.1001/jama.2020.21218 ↩ ↩2 ↩3 ↩4
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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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Study of urine drug testing after pure CBD and CBD-dominant cannabis, 2019. https://pubmed.ncbi.nlm.nih.gov/31682266/ ↩ ↩2 ↩3
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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 ↩ ↩2
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Royal Australian and New Zealand College of Psychiatrists. Updated clinical memorandum: therapeutic use of medicinal cannabis, 2024. https://ranzcp.org/news-analysis/updated-clinical-memorandum-therapeutic-use-of-medicinal-cannabis ↩
-
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 ↩
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Filippini G, et al. Cannabis and cannabinoids for symptomatic treatment for people with multiple sclerosis. Cochrane Database of Systematic Reviews, 2022. https://pubmed.ncbi.nlm.nih.gov/35510826/ ↩
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Moore A, 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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Dahlgren MK, et al. Urinary tetrahydrocannabinol after 4 weeks of a full-spectrum, high-cannabidiol treatment. JAMA Psychiatry, 2021. https://pubmed.ncbi.nlm.nih.gov/33146684/ ↩
Common questions
Is CBD or THC stronger?
They are not stronger or weaker versions of each other. They are different compounds with different effects. In one controlled study 10 mg of THC was intoxicating while 600 mg of CBD was no different from placebo. Trials use much larger doses of CBD than of THC for that reason.
Does CBD cancel out THC?
Not reliably. Some studies suggest CBD can reduce certain effects of THC, but in a controlled study of 31 cannabis smokers, up to 800 mg of CBD taken beforehand did not reduce the high from smoked cannabis.
Do CBD and THC come from different plants?
No. Both come from the same species, Cannabis sativa. Varieties grown for fibre and seed (hemp) make mostly CBD and little THC. Varieties grown as a drug make mostly THC.
Can a CBD product contain THC?
Yes. Full-spectrum CBD products contain small amounts of THC by design, and studies of unregulated products sold online have found THC in some that claimed to have none. Small amounts of THC can be enough to produce a positive drug test.
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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