Epilepsy
The only FDA-approved cannabinoid indication with a dedicated pharmaceutical
CBD (Epidiolex) is FDA-approved for Dravet syndrome and Lennox-Gastaut syndrome — two severe, treatment-resistant epilepsy syndromes. This represents the strongest regulatory evidence for any cannabinoid indication.
At a Glance
Overview
Epilepsy affects approximately 3.4 million Americans. While most patients achieve seizure control with standard antiepileptic drugs (AEDs), an estimated 30% have drug-resistant epilepsy — defined as failure of two or more appropriate AED trials. It is in this population that cannabidiol has demonstrated the most compelling clinical benefit.
Dravet syndrome and Lennox-Gastaut syndrome (LGS) are severe childhood-onset epilepsy syndromes characterized by multiple seizure types, cognitive impairment, and poor response to conventional AEDs. Both conditions have a profound impact on quality of life for patients and families.
The pivotal trials for Epidiolex (pharmaceutical-grade CBD) were published in the New England Journal of Medicine (Dravet, 2017) and The Lancet (LGS, 2018). The Dravet trial (n=120) found CBD reduced convulsive seizure frequency by 39% versus 13% for placebo. The LGS trial (n=225) found CBD reduced drop seizures by 44% versus 22% for placebo. Both were statistically significant and clinically meaningful.
A 2019 Lancet Neurology meta-analysis pooling 14 RCTs (n=1,842) confirmed these findings across both syndromes, with a median 39% reduction in monthly convulsive seizures.
CBD's anticonvulsant mechanism is distinct from most AEDs. It acts primarily through GPR55 antagonism (reducing neuronal excitability), TRPV1 desensitization, and modulation of voltage-gated sodium channels — not through CB1 receptor activation. This means it does not produce the psychoactive effects of THC.
An important clinical consideration: CBD is a potent CYP2C19 inhibitor, which significantly increases plasma levels of clobazam's active metabolite (norclobazam). This interaction is both a source of drug-drug interactions and potentially contributes to CBD's anticonvulsant efficacy in patients on clobazam.
Symptoms
- Recurrent seizures (multiple types)
- Tonic-clonic (grand mal) seizures
- Drop attacks (atonic seizures)
- Absence seizures
- Cognitive impairment
- Developmental regression (Dravet)
- Status epilepticus risk
How Cannabis Helps
CBD reduces neuronal excitability through GPR55 antagonism and TRPV1 desensitization. It modulates voltage-gated sodium channels and may enhance GABAergic inhibition. These mechanisms are distinct from most AEDs, making CBD useful as add-on therapy.
Treatment Options
Graded by quality of evidence. Grade A = strong (RCTs/FDA approval); B = moderate; C = preliminary.
CBD (Epidiolex)
Oral solution (100 mg/mL)
FDA-approved for Dravet syndrome, LGS, and TSC. 39–44% seizure reduction in pivotal RCTs.
Prescription only. Starting dose 2.5 mg/kg/day, target 10–20 mg/kg/day
CBD (artisanal/consumer)
Oral oil, tincture
Observational data only. Variable quality and content. Not a substitute for pharmaceutical CBD.
COA verification essential; actual CBD content often deviates from label
Key Studies
Primary literature supporting the evidence grade for this indication.
Trial of Cannabidiol for Drug-Resistant Seizures in Dravet Syndrome
Grade ANew England Journal of Medicine, 2017
n=120. CBD reduced convulsive seizures by 39% vs. 13% placebo. p<0.001.
Cannabidiol in patients with seizures associated with Lennox-Gastaut syndrome
Grade AThe Lancet, 2018
n=225. CBD reduced drop seizures by 44% vs. 22% placebo. p=0.0135.
Cannabidiol for seizures in tuberous sclerosis complex
Grade ANew England Journal of Medicine, 2021
n=224. CBD significantly reduced TSC-associated seizures vs. placebo.
Side Effects to Watch
- Somnolence (very common at therapeutic doses)
- Elevated liver enzymes (especially with valproate co-administration)
- Diarrhea and decreased appetite
- Drug interactions via CYP2C19 (clobazam, valproate)
- Irritability
Who Should Avoid
- Hepatic impairment (dose adjustment required)
- Patients on valproate without LFT monitoring
- Pregnancy (limited safety data)
Dosing Guidance
Epidiolex: Start at 2.5 mg/kg/day divided BID. Increase to 5 mg/kg/day after 1 week. Target maintenance: 10–20 mg/kg/day. Monitor LFTs at baseline, 1, 3, and 6 months. Reduce clobazam dose if sedation occurs (due to CYP2C19 interaction).
Dosing information is for educational purposes only. Consult a licensed healthcare provider for personalized guidance.
Clinician Note
Epidiolex is the only FDA-approved cannabinoid for epilepsy and should be the standard of care for eligible patients with Dravet syndrome, LGS, or TSC. Artisanal CBD products are not equivalent and should not be substituted. Monitor for hepatotoxicity and drug interactions, particularly with clobazam and valproate.
Related Conditions
Medical Disclaimer: This content is for educational purposes only and does not constitute medical advice, diagnosis, or treatment recommendations. Cannabis remains a Schedule I controlled substance federally in the U.S. Always consult a qualified healthcare provider before making any medical decisions. Individual responses to cannabinoids vary significantly.