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CBD for epilepsy

Large trials found high-dose prescription CBD, added to other medicines, reduced seizures in three rare, severe epilepsies. It is not proven for common adult epilepsy.

Facts checked 13 November 20267 min readHow we research
Strong evidence

Strong for Dravet syndrome, Lennox-Gastaut syndrome and tuberous sclerosis complex only, as an add-on prescription medicine at 10 to 25 mg/kg a day. Not enough evidence for common adult epilepsies.

How we grade evidence

Epilepsy is the only condition where CBD has strong evidence. Large placebo-controlled trials found that a purified prescription CBD medicine, added to existing treatment, reduced seizures in three rare and severe syndromes: Dravet syndrome, Lennox-Gastaut syndrome and tuberous sclerosis complex. The doses were high, and for common adult epilepsies there is not enough evidence to say whether CBD does anything.

What the research shows

All of the main trials tested the same thing: purified CBD oral solution or placebo, added to the seizure medicines people were already taking.

Trial Who Daily CBD dose Result
Devinsky 2017 120 children and young adults with Dravet syndrome 20 mg/kg Convulsive seizures fell from a median of 12.4 to 5.9 a month on CBD, and from 14.9 to 14.1 on placebo1
GWPCARE4 (Thiele 2018) 171 people aged 2 to 55 with Lennox-Gastaut syndrome 20 mg/kg Drop seizures fell by a median of 43.9% on CBD and 21.8% on placebo2
GWPCARE3 (Devinsky 2018) 225 people aged 2 to 55 with Lennox-Gastaut syndrome 10 or 20 mg/kg Drop seizures fell by 41.9% (20 mg/kg), 37.2% (10 mg/kg) and 17.2% (placebo)3
GWPCARE6 (Thiele 2021) 224 people with tuberous sclerosis complex 25 or 50 mg/kg Seizures fell by 48.6% (25 mg/kg), 47.5% (50 mg/kg) and 26.5% (placebo)4

A drop seizure is one that makes a person suddenly fall. Tuberous sclerosis complex is a genetic condition that causes growths in the brain and other organs, and often seizures.

Some points keep these results in proportion:

  • Few people became seizure-free. In the Dravet trial, 5% of the CBD group had no convulsive seizures, compared with none on placebo. The share of people whose seizures at least halved (43% against 27%) was not a statistically significant difference.1
  • Placebo groups improved too, by about 17% to 27% in the Lennox-Gastaut and tuberous sclerosis trials.234
  • The higher dose was not better in tuberous sclerosis. The 50 mg/kg dose worked no better than 25 mg/kg and had a worse safety profile.4
  • Part of the effect may come from an interaction. CBD raises the blood level of the active breakdown product of clobazam, a common seizure medicine, about three-fold. Many trial participants were taking clobazam.5

A 2026 meta-analysis (a study that pools trials) covered 7 randomised trials and 1,154 participants. It found the effect was consistent across the three syndromes.6 An earlier systematic review of 6 trials and 555 patients reached a more careful conclusion: add-on CBD may reduce seizures in severe drug-resistant epilepsy, but bias could explain some of the effect.7 A review of trials in children found CBD probably reduces seizures in drug-resistant childhood epilepsy, with monthly seizure frequency about 20% lower than placebo.8

Longer follow-up exists. In an open-label extension (where everyone knows they are taking CBD), reductions in drop seizures of 48% to 71% were maintained through 156 weeks. With no placebo group, this cannot show how much of that was due to CBD.9

What about other kinds of epilepsy?

The trials above involved rare syndromes that had not responded to other medicines. They do not tell us whether CBD works in the more common epilepsies that most adults have. The TGA’s guidance says the evidence is strongest for children, and that there is not enough evidence to recommend it for adults.10

What doses were tested

The trials used 10 to 25 mg of CBD per kilogram of body weight each day.5 For a 70 kg adult, the Dravet and Lennox-Gastaut range of 10 to 20 mg/kg works out to about 700 to 1,400 mg a day, and the 25 mg/kg used for tuberous sclerosis complex to about 1,750 mg.

That is far above what most people picture when they think of CBD oil. The Australian limit for pharmacist-only (Schedule 3) CBD is 150 mg a day,11 and an Australian review noted that very low doses of about 5 to 25 mg have little evidence of any health benefit.12 No trial has shown that low-dose CBD reduces seizures.

The registered medicine is started low and increased in weekly steps, with the dose set by the prescriber according to body weight, liver function and other medicines.5 See the CBD dosage guide for how prescribers approach this.

What Australian medical bodies say

  • TGA. The Therapeutic Goods Administration registered Epidyolex (cannabidiol 100 mg/mL oral solution) in September 2020 as an add-on therapy for seizures associated with Lennox-Gastaut syndrome or Dravet syndrome in patients aged two years and older.13 More detail is on our page about the registered cannabis medicines.
  • Tuberous sclerosis complex. We could not confirm that this is an approved use in Australia. A submission to subsidise CBD for tuberous sclerosis complex was lodged for the November 2026 meeting of the Pharmaceutical Benefits Advisory Committee. It had not been listed as of the last official update on 23 July 2026.14
  • NPS MedicineWise. Its evidence summary calls the evidence base limited, notes that most studies were rated moderate to very low quality, and lists diarrhoea, sleepiness and decreased appetite as the most common adverse events.15
  • RACGP. The Royal Australian College of General Practitioners describes the evidence for CBD plus seizure medicines achieving a greater than 50% seizure reduction as low to very low quality.16

Risks to know about

Side effects were common at the doses used in epilepsy trials.

  • Sleepiness. Sleepiness or sedation affected 32% of people on CBD against 11% on placebo. Among people also taking clobazam it was 46%.5
  • Liver. Liver enzymes rose to more than three times the normal upper limit in 13% of people on CBD in the Lennox-Gastaut and Dravet trials, against 1% on placebo. The rate was 30% in people also taking both valproate and clobazam. The label calls for liver blood tests before starting and at 1, 3 and 6 months.5 See CBD and the liver.
  • Interactions. CBD changes the levels of several seizure medicines, including clobazam and stiripentol.5 See CBD drug interactions.
  • Other effects. Decreased appetite, diarrhoea, rash and tiredness were also reported more often than with placebo.5
  • Stopping suddenly. As with other seizure medicines, the label warns against stopping abruptly because of the risk of more seizures.5
  • Sesame. The registered oral solution contains sesame oil and is not suitable for people with sesame allergy.5

Unregulated products add another risk. If the amount of CBD in a bottle is not what the label says, seizure control and medicine levels can change without warning. See is what is on the label in the bottle?.

If you are considering it

  • Talk to the neurologist or paediatrician who manages the epilepsy before anything else. CBD for epilepsy is specialist treatment. Our page on CBD for children and teenagers has more for parents.
  • Do not add CBD to seizure medicines, or swap them for CBD, without medical supervision.
  • Questions worth asking: Is the diagnosis one of the syndromes that was studied? Which current medicines interact with CBD? How will liver function be monitored? How will we judge whether it is working, and when would we stop?

Footnotes

  1. Devinsky O, et al. Trial of cannabidiol for drug-resistant seizures in the Dravet syndrome. New England Journal of Medicine, 2017. https://doi.org/10.1056/NEJMoa1611618 ↩ ↩2

  2. Thiele EA, et al. Cannabidiol in patients with seizures associated with Lennox-Gastaut syndrome (GWPCARE4). The Lancet, 2018. https://pubmed.ncbi.nlm.nih.gov/29395273/ ↩ ↩2

  3. Devinsky O, et al. Effect of cannabidiol on drop seizures in the Lennox-Gastaut syndrome (GWPCARE3). New England Journal of Medicine, 2018. https://pubmed.ncbi.nlm.nih.gov/29768152/ ↩ ↩2

  4. American Epilepsy Society. Abstract of the GWPCARE6 phase 3 trial of cannabidiol in tuberous sclerosis complex (published as Thiele et al., JAMA Neurology, 2021). https://aesnet.org/abstractslisting/efficacy-and-safety-of-cannabidiol-cbd-for-seizures-associated-with-tuberous-sclerosis-complex-tsc-in-pediatric-and-adult-patients-from-gwpcare6-a-phase-3-trial-with-open-label-extension-ole ↩ ↩2 ↩3

  5. 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

  6. Meta-analysis of seven randomised trials of highly purified cannabidiol in Dravet syndrome, Lennox-Gastaut syndrome and tuberous sclerosis complex, 2026. https://pubmed.ncbi.nlm.nih.gov/42179430/ ↩

  7. NIHR Evidence. Summary of Stockings et al., systematic review of cannabinoids for epilepsy, Journal of Neurology, Neurosurgery and Psychiatry, 2018. https://evidence.nihr.ac.uk/?p=38801 ↩

  8. Systematic review of cannabidiol for drug-resistant epilepsy in children, 2018. https://pubmed.ncbi.nlm.nih.gov/30515765/ ↩

  9. Open-label extension of cannabidiol in Lennox-Gastaut syndrome, Epilepsia, 2021 (repository copy). https://discovery.ucl.ac.uk/id/eprint/10126054/1/epi.16878.pdf ↩

  10. Therapeutic Goods Administration. Guidance for the use of medicinal cannabis in the treatment of epilepsy in paediatric and young adult patients in Australia. https://www.tga.gov.au/resources/publication/publications/guidance-use-medicinal-cannabis-treatment-epilepsy-paediatric-and-young-adult-patients-australia ↩

  11. Therapeutic Goods Administration. Final decision on down-scheduling of low-dose cannabidiol, 2020. https://tga.gov.au/node/284859 ↩

  12. Arnold JC, et al. Prescribing medicinal cannabis. Australian Prescriber, 2020. https://www.nps.org.au/assets/p152-Arnold-et-al.pdf ↩

  13. Therapeutic Goods Administration. Australian prescription medicine decision summary: Epidyolex. https://www.tga.gov.au/resources/auspmd/epidyolex ↩

  14. Pharmaceutical Benefits Scheme. Medicine status: cannabidiol for tuberous sclerosis complex, updated 23 July 2026. https://www.pbs.gov.au/medicinestatus/document/1675 ↩

  15. NPS MedicineWise. Medicinal cannabis evidence summary: epilepsy in young patients. https://www.nps.org.au/assets/Medicinal-cannabis-evidence-summary-epilepsy-in-young-patients.pdf ↩

  16. Royal Australian College of General Practitioners. Position statement: use of medicinal cannabis products in Australia (2019 update). https://www.racgp.org.au/advocacy/position-statements/view-all-position-statements/clinical-and-practice-management/medical-cannabis ↩

Common questions

Does CBD help epilepsy?

In three rare and severe epilepsy syndromes (Dravet, Lennox-Gastaut and tuberous sclerosis complex), large trials found that prescription CBD added to existing medicines reduced seizures more than placebo. For other types of epilepsy, including the common adult forms, there is not enough evidence to say.

Can I use low-dose CBD oil for seizures?

There is no trial evidence that low-dose CBD reduces seizures. The trials that showed an effect used 10 to 25 mg per kilogram of body weight a day, which is many times more than low-dose products supply. Anyone with epilepsy should talk to their neurologist before taking CBD, because it changes the blood levels of some seizure medicines.

Is Epidyolex approved in Australia?

Yes. The TGA registered Epidyolex, a purified CBD oral solution, in September 2020 as an add-on treatment for seizures in Lennox-Gastaut syndrome or Dravet syndrome in patients aged two years and older.

Can CBD replace my epilepsy medicine?

The trials tested CBD as an addition to existing seizure medicines, not as a replacement. Stopping a seizure medicine suddenly can cause more seizures. Any change should be made by the doctor who manages your epilepsy.

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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