What happens when you take cbd with clobazam?
Clobazam is a 1,5-benzodiazepine used widely for refractory epilepsy, particularly Lennox-Gastaut and Dravet syndromes. The parent drug is N-demethylated by CYP3A4 to N-desmethylclobazam (N-CLB), an active metabolite that accumulates to plasma concentrations several-fold higher than clobazam itself and is responsible for much of the sedative effect. N-CLB is then cleared mainly by CYP2C19. Cannabidiol (CBD) is a potent inhibitor of CYP2C19 - inhibition constants in the low micromolar range, easily reached with anti-seizure doses of Epidiolex.
When CBD is added to a stable clobazam regimen, CYP2C19 inhibition slows N-CLB clearance. In a pivotal interaction study summarized in the FDA Epidiolex label, co-administration of CBD increased N-desmethylclobazam plasma concentrations approximately 3-fold, while clobazam itself rose by a smaller amount. Clinical trial investigators reported sharply higher rates of somnolence in patients on the combination, and pharmacokinetic studies in pediatric epilepsy clinics have shown similar magnitudes.
Why is this important?
The combination is so common - and the interaction so reliable - that the Epidiolex label specifically addresses concurrent clobazam use. Many children and adults on Epidiolex are already on clobazam because both drugs are first- and second-line agents for the same rare epilepsies. Without anticipating the interaction, patients can experience excessive somnolence, hypotonia (low muscle tone), sialorrhea (drooling), ataxia, and confusion within days to weeks of starting CBD. In small children with refractory epilepsy, sedation can be misinterpreted as worsening neurological status, a postictal state, or a new medical illness.
The interaction also has a few important wrinkles. The increase in N-CLB is delayed because the metabolite has a long half-life (~70 hours in adults, longer in children), so somnolence may not peak until 1-2 weeks after starting CBD - well after a typical follow-up visit. CYP2C19 is genetically variable; poor metabolizers (common in East Asian populations) start out with higher N-CLB levels and may experience exaggerated effects. And the interaction goes both ways: clobazam mildly increases CBD exposure through unclear mechanisms.
What should you do?
This is one of the most clinically important CBD interactions and is best managed by the prescribing neurologist or epileptologist, not by self-titration.
- Tell the prescriber about all CBD use, including over-the-counter hemp products, before starting or escalating either drug.
- Expect a planned clobazam dose reduction. The Epidiolex label states that a reduction in clobazam dose should be considered if adverse reactions known to occur with clobazam are experienced when administered with Epidiolex; in practice, many epilepsy programs preemptively cut clobazam by 25% when starting CBD at 10 mg/kg/day, with further reductions at higher CBD doses.
- Ask about therapeutic drug monitoring for both clobazam and N-desmethylclobazam if your center offers it. Targeting N-CLB levels can keep efficacy without oversedation.
- Watch for sedation signs: excessive sleepiness, slurred speech, increased drooling, unsteady gait, behavioral change, or loss of appetite. Report these promptly rather than waiting for the next routine visit.
- Be cautious with other CNS depressants: opioids, benzodiazepines, alcohol, and gabapentin/pregabalin all add to sedation.
Which specific products are affected?
The interaction has been formally characterized for pharmaceutical Epidiolex (cannabidiol oral solution) with clobazam (Onfi, Sympazan, Frisium). The same mechanism applies to consumer CBD products - tinctures, oils, gummies, capsules, vapes - but the magnitude is dose-dependent and the bioavailability of consumer products is highly variable, so the interaction may be smaller in absolute terms but is still real. Full-spectrum and broad-spectrum hemp extracts contain the same cannabidiol and behave the same way. THC-containing cannabis products add their own CNS depression risk and should be considered additive. Clobazam is sold as Onfi, Sympazan (oral film), Frisium, Tapclob, and various generics; all share the same metabolic pathway.
The bottom line
Adding CBD to clobazam produces a reliable, well-characterized 3-fold rise in the active metabolite N-desmethylclobazam, which translates into excess sedation in a large fraction of patients. The interaction is built into the FDA Epidiolex label and is managed routinely in epilepsy clinics through anticipatory clobazam dose reduction and N-CLB monitoring. If you or your child takes clobazam, do not add any CBD product - including over-the-counter hemp oils - without the prescriber's involvement.