Cannabinoids and epilepsy

Epilepsy is one of the few conditions where the data for cannabinoids goes beyond anecdote. But the gap between “cannabis for epilepsy” and “a specific preparation that works for a specific seizure type” is wide, and the New Zealand prescribing pathway reflects that. the material below names the condition, the outcome, the preparation and the strength of support for each claim, so you can walk into a GP appointment with realistic expectations and the right questions.

Do cannabinoids work for epilepsy, and if so, which medicine, for which seizure type?

The short answer: two purified cannabinoid medicines have strong backing for two rare, severe childhood epilepsy syndromes. General cannabis preparations have weaker support for other epilepsy types. The legal pathway in New Zealand runs through a prescription, not a general cannabis licence.

What the research actually shows

The strongest clinical support for cannabinoids in epilepsy is for Epidyolex (cannabidiol, CBD) as an add-on treatment for two rare, severe syndromes:

• Dravet syndrome, a developmental epileptic encephalopathy beginning in infancy.
• Lennox-Gastaut syndrome (LGS), a childhood-onset epilepsy with multiple seizure types.

Quality of the data: high, based on multiple randomised, placebo-controlled trials. These include a 2018 systematic review and meta-analysis by Stockings et al. (published in the International Journal of Drug Policy) and the 2018 update of the Cochrane review on cannabinoids for epilepsy. In these trials, pharmaceutical CBD (Epidyolex) reduced seizure frequency by 50% or more in a significantly larger proportion of patients than placebo. The effect was consistent across three randomised trials (two in Dravet syndrome, one in LGS). The CBD used was a purified oral solution, not a whole-plant extract.

Outcome metrics from the pivotal trials

In the 2017 trial of CBD for Dravet syndrome (Devinsky et al., New England Journal of Medicine, N=120), the percentage of patients with a ≥50% reduction in convulsive seizures was 43% for CBD 20 mg/kg/day versus 27% for placebo. The 20 mg/kg/day group had a median monthly convulsive seizure reduction of 41% (IQR 0-69) versus 13% for placebo.

In the 2018 LGS trial (Devinsky et al., NEJM), CBD 20 mg/kg/day reduced drop seizures by a median of 44% versus 17% for placebo. Another LGS trial reported a median reduction of 41.9% for CBD versus 13.3% for placebo.

These figures come from the published trials. They are not a guarantee of individual response. The data are specific to Epidyolex (pure CBD oral solution) in these two syndromes, not to cannabis flower or oils generally.

What the 2024 ILAE review concluded

The 2024 systematic review by the International League Against Epilepsy (ILAE) concluded there is high-quality support for pharmaceutical CBD (Epidyolex) in Dravet and Lennox-Gastaut syndromes, but not for other epilepsy types. That review is the single most authoritative recent summary.

Adverse events to watch for

Adverse events were more common with CBD than placebo. Diarrhoea, somnolence, decreased appetite and transaminase elevations were the most frequent. High THC doses can lower the seizure threshold in some patients. THC is not used as a first-line anti-seizure treatment. It is more likely to be prescribed as an adjunct for pain or spasticity.

The New Zealand prescribing pathway

How the Medicinal Cannabis Scheme works

The Medicinal Cannabis Scheme (Misuse of Drugs (Medicinal Cannabis) Regulations 2019) has been in force since 1 April 2020. Medsafe approves products. The Medicinal Cannabis Agency (MCA) issues licences. The Ministry of Health’s 2022 review of the scheme confirmed that no product has yet been fully approved under the scheme. All products are prescribed under Section 29 of the Misuse of Drugs Act (for CBD) or Section 22B for THC-containing products. The prescription must be issued by a medical practitioner. It is an offence to supply without a prescription.

What the NZ Formulary says

The NZ Formulary (2025) lists CBD as a monitored medicine, meaning prescriptions are tracked. Its cannabis product monograph states that support for CBD in epilepsy is strongest for Dravet syndrome and LGS, based on randomised controlled trials. For other epilepsy types, the data are limited. The Formulary does not list cannabis as a treatment for anxiety, depression or sleep as a primary indication. Clinicians are advised to prescribe only products that meet GMP standards.

Which product has a formal indication

Epidyolex (pure CBD, 100 mg/mL) is the only CBD product with a formal indication for seizures. It is approved for Dravet syndrome, LGS and tuberous sclerosis complex. From April 2024 it is funded for patients under 18 with Dravet or LGS, and for treatment-resistant epilepsy in tuberous sclerosis complex. For other patients, Epidyolex is not subsidised and costs several thousand dollars per month.

What you need to know about other cannabis preparations

There is no high-quality support showing that smoked flower reduces seizures. The only condition-specific data for epilepsy are for purified CBD (Epidyolex), not for whole-plant cannabis products. Systematic reviews and clinical guidance consistently note that high-quality trials are limited, that most data are short-term, and that many claimed benefits are not supported by controlled studies. Healthify notes that cannabis-based medicines are not first-line treatment for any condition, and the clearest data for epilepsy are for certain rare childhood epilepsies (Dravet syndrome and LGS).

How to use this information at your appointment

• Ask whether your seizure type matches one of the syndromes for which purified CBD has strong support.
• Confirm that any product discussed is a GMP-standard oral solution, not a whole-plant extract or smoked flower.
• Request the specific responder-rate figures from the pivotal trials so you can weigh likely benefit against the adverse-event profile.
• Check the current funding status of Epidyolex for your age group and diagnosis.
• Verify that the prescribing doctor is registered and that the product meets the Medicinal Cannabis Scheme requirements.