Can Tetrahydrocannabinol (THC) cause seizures?

Can THC Cause Seizures?

Yes, THC can cause seizures, particularly with high-potency products and concentrated forms, though the relationship is complex and paradoxical—cannabis can both trigger and suppress seizures depending on multiple factors including THC concentration, CBD content, and individual susceptibility. 1, 2

The Paradoxical Nature of THC and Seizures

The evidence reveals a critical paradox that clinicians must understand:

• Whole-plant cannabis can paradoxically both contribute to and reduce seizures, making its use problematic without standardization and quality control 3
• High-dose THC concentrates (up to 70% THC) are particularly concerning for seizure provocation, especially in adolescents and those without prior seizure history 1, 4
• The average THC concentration has nearly doubled from 9% in 2008 to 17% in 2017, substantially elevating seizure risk 4, 5

Clinical Evidence of THC-Induced Seizures

Case Reports and Direct Evidence

• A 17-year-old with no seizure history developed a generalized tonic-clonic seizure after daily vaping of concentrated THC ("wax"), with EEG showing epileptiform discharges that resolved after THC cessation 1
• Pediatric marijuana ingestion cases have documented seizures as a severe complication, particularly in young children exposed to edible products 6
• The clinical and EEG findings in these cases were temporally associated with THC use, suggesting THC can lower seizure threshold and generate epileptiform discharges 1

Species-Specific Vulnerability

• Animal studies demonstrate species-specific susceptibility to cannabis-induced convulsions, with rats developing spontaneous generalized seizures and epileptiform discharges after prolonged THC exposure, while dogs did not 2
• This suggests important interspecies variations in endocannabinoid signaling that may affect seizure susceptibility 2

High-Risk Populations

Adolescents and Children

• Adolescents face elevated risks including neurodevelopmental decline and should avoid cannabis use entirely 3, 7
• Unintentional pediatric exposures increased from 207 cases in 2017 to 3,054 in 2021, with some causing central nervous system depression and seizures 4
• Marijuana products have the potential to provoke seizures and affect the developing brain, making self-medication particularly dangerous in households with children 6

Patients with Epilepsy

• Patients with existing epilepsy using cannabis face unpredictable effects—while pharmaceutical-grade CBD (Epidiolex) is FDA-approved for specific rare epilepsy syndromes, whole-plant cannabis with variable THC content is not recommended 3
• Some pediatric drug-resistant epilepsy cases that failed high-dose CBD showed improvement with THC addition, but this requires careful medical supervision 8

Critical Clinical Distinctions

FDA-Approved vs. Recreational Products

• Only pharmaceutical-grade CBD (Epidiolex) is FDA-approved for seizure disorders (Dravet syndrome, Lennox-Gastaut syndrome, tuberous sclerosis complex), not THC-containing products 3, 7
• Medical marijuana itself has NOT been FDA-approved for any indication despite state-level legalization 7
• The lack of standardization in recreational cannabis products makes seizure risk unpredictable 3

Concentration Matters

• Cannabis concentrates with THC levels up to 70% pose substantially higher seizure risk than traditional plant material 4, 5
• No hepatotoxicity cases were reported with CBD doses under 300 mg/day, but seizure risk with THC is dose-dependent 4

Common Pitfalls to Avoid

1. Do not assume cannabis is uniformly anticonvulsant—the THC component can be proconvulsant, especially at high concentrations 1, 2

2. Do not overlook concentrated THC products (wax, dabs, vaping concentrates) as potential seizure triggers in patients presenting with new-onset seizures 1

3. Do not dismiss marijuana exposure in children with unexplained drowsiness or seizures—consider urine THC testing in unexplained pediatric encephalopathy 6

4. Do not confuse CBD's anticonvulsant properties with THC's effects—they act through different mechanisms and have opposite seizure profiles 3, 9

Clinical Recommendations

• Screen for concentrated THC use in adolescents and young adults presenting with new-onset seizures, particularly if other etiologies are unrevealing 1
• Counsel patients with epilepsy to avoid recreational cannabis products due to unpredictable THC content and paradoxical seizure risk 3
• Consider THC as a potential seizure trigger in the differential diagnosis, especially with high-potency products and in previously seizure-free individuals 1, 6
• Monitor for worsening symptoms if patients are using cannabis therapeutically—consider dose reduction or discontinuation if seizures increase 7