Does CBD help seizures in tuberous sclerosis?

Yes. This large RCT found CBD at 25 mg/kg/day reduced TSC-associated seizures by 48.6% compared to 26.5% for placebo, a significant 30.1% improvement over placebo.

Is the higher dose better?

No. The 50 mg/kg/day dose was not more effective (47.5% reduction) but caused substantially more side effects, including diarrhea (56% vs 31%) and somnolence (26% vs 13%). The lower dose had a better risk-benefit profile.

Randomized Controlled TrialStrong Evidence2021

CBD Reduced Seizures by About 49% in Tuberous Sclerosis Complex

Add-on Cannabidiol Treatment for Drug-Resistant Seizures in Tuberous Sclerosis Complex: A Placebo-Controlled Randomized Clinical Trial.

In a landmark placebo-controlled trial of 224 patients with tuberous sclerosis complex, cannabidiol at 25 mg/kg/day reduced seizures by 48.6% compared to 26.5% for placebo, with the lower dose showing a better safety profile.

The Dravet trial proved CBD worked for one catastrophic epilepsy. The Lennox-Gastaut trial proved it worked for a second. But both conditions primarily involve generalized seizures — electrical storms that sweep across the entire brain. The question remained: would CBD work for focal seizures, where the electrical chaos starts in one specific region?

Tuberous sclerosis complex was the test case. TSC is a genetic disease that grows non-cancerous tumors throughout the body — brain, kidneys, heart, skin, lungs. In the brain, these growths called cortical tubers create focal seizure hotspots. About 80-90% of TSC patients develop epilepsy, often before their first birthday. The seizures are focal first, though they frequently generalize. And they resist medication.

If CBD worked here — in a structurally different disease with primarily focal seizures — it would prove that cannabidiol's anticonvulsant mechanism was truly broad-spectrum.

The Disease

The Trial

The Results

48.6% vs. 47.5%

seizure reduction at the 25 mg/kg/day and 50 mg/kg/day doses — virtually identical efficacy. But the adverse event profile was dramatically different: diarrhea jumped from 31% to 56%, somnolence from 13% to 26%, and discontinuations from 11% to 14% at the higher dose. More CBD was not better — it was just more toxic.

This is the first CBD epilepsy trial to demonstrate a clear dose ceiling. The Dravet and LGS trials tested only 20 mg/kg/day. This trial showed that doubling the dose adds side effects without adding benefit.

Thiele et al. (2021), JAMA Neurol 78:285-292

Why This Trial Changed the Conversation

The Liver Signal

Myth vs. Reality

✕Myth

CBD is completely safe because it's natural and non-psychoactive.

✓Reality

At therapeutic epilepsy doses, CBD causes elevated liver transaminase levels in 18.9% of patients — nearly 1 in 5. Zero patients on placebo had this finding. The elevation is dose-dependent and worsened by concurrent valproate use. While most cases are reversible with dose reduction, it requires regular blood monitoring. At therapeutic doses, CBD is a drug with real hepatotoxicity risk, not a harmless supplement. This is why Epidiolex is prescription-only with mandated liver function monitoring.

The Evidence

Thiele et al. (2021): 18.9% of CBD patients had elevated liver transaminases vs 0% placebo. Dose-dependent: higher rates at 50 mg/kg/day. Interaction with valproate documented across all three Epidiolex trials (Dravet, LGS, TSC).

Thiele et al. (2021), JAMA Neurol 78:285-292

Frequently Asked Questions

TSC is a genetic disease (affecting ~1 in 6,000 people) caused by mutations in the TSC1 or TSC2 gene, which normally suppress cell growth via the mTOR pathway. When these genes are dysfunctional, benign tumors grow in the brain, kidneys, heart, lungs, and skin. In the brain, growths called cortical tubers create seizure hotspots. About 80-90% of TSC patients develop epilepsy, often in the first year of life. Seizures are typically focal (starting in one brain region) and frequently resist medication.

No. This trial specifically showed that 25 mg/kg/day was as effective as 50 mg/kg/day (48.6% vs 47.5% seizure reduction) but with substantially fewer side effects — diarrhea dropped from 56% to 31%, somnolence from 26% to 13%. The clinical recommendation is to use the lower effective dose. More CBD is not better for seizure control and comes with significantly more adverse effects and hepatotoxicity risk.

CBD has now been proven effective in three distinct epilepsy types: Dravet syndrome (genetic channelopathy, generalized seizures), Lennox-Gastaut syndrome (heterogeneous causes, drop seizures), and tuberous sclerosis complex (structural, focal seizures). This breadth suggests a broad-spectrum anticonvulsant mechanism. However, CBD has not been studied in all epilepsy types, and efficacy in these three severe conditions does not guarantee it will work for milder or different forms. Clinical trials for other indications are ongoing.

CBD Epilepsy

Cite this study

Thiele, Elizabeth A; Bebin, E Martina; Bhathal, Hari; Jansen, Floor E; Kotulska, Katarzyna; Lawson, John A; O'Callaghan, Finbar J; Wong, Michael; Sahebkar, Farhad; Checketts, Daniel; Knappertz, Volker. (2021). Add-on Cannabidiol Treatment for Drug-Resistant Seizures in Tuberous Sclerosis Complex: A Placebo-Controlled Randomized Clinical Trial.. JAMA neurology, 78(3), 285-292. https://doi.org/10.1001/jamaneurol.2020.4607

View on PubMed

More from these researchers

Thiele, Elizabeth A(7)Bebin, E Martina(4)Bhathal, Hari(2)