Short answer

One cannabis-based medicine carries FDA approval for epilepsy: Epidiolex, a purified cannabidiol (CBD) oral solution. It treats seizures tied to Dravet syndrome, Lennox-Gastaut syndrome, and tuberous sclerosis complex. No whole-plant cannabis product, THC edible, or over-the-counter CBD oil has FDA approval for epilepsy. Epidiolex is a Schedule V prescription drug under federal law. State-licensed cannabis remains Schedule I.

What the FDA approved, and when

Dose runs from 2.5 mg per kg of body weight per day to 20 mg/kg/day, with a top dose of 25 mg/kg/day in some cases. A prescriber sets the dose. The drug is taken by mouth twice daily.

What trials measured

Double-blind, placebo-controlled trials ran from 2016 to 2019. Patients stayed on their other seizure medicines. Median monthly seizure frequency dropped by about 38% to 44% on CBD, against about 13% to 27% on placebo. A share of patients saw seizure counts fall by half or more. No trial reported seizure freedom for most patients. Response varied by syndrome, seizure type, and dose.

THC and epilepsy

THC has no large randomized trials for seizure control. Some patients report benefit from THC-rich products, but that evidence is small and self-reported. THC causes intoxication and can impair memory and balance. Evidence on how THC affects seizure threshold is mixed; case reports describe seizures during withdrawal after heavy use. Tell your neurologist if you use THC.

Side effects and drug interactions

Common side effects in trials: drowsiness, decreased appetite, diarrhea, vomiting, fatigue, and fever. Liver enzyme levels rose in a portion of patients, so prescribers check liver blood work at baseline and during dose increases. CBD inhibits drug-metabolizing enzymes and can raise blood levels of clobazam, valproate, and other antiseizure drugs. Patients on valproate carry a higher risk of liver enzyme elevation and sedation.

Retail CBD versus prescription CBD

These are not the same product. FDA testing found commercial CBD products with little or no CBD, mislabeled THC, synthetic cannabinoids, and traces of heavy metals or pesticides. Dose control matters for epilepsy because dosing is based on body weight and titration steps are narrow. A bottle labeled "CBD 500 mg" can differ batch to batch.

State medical cannabis programs

Medical cannabis for epilepsy is legal in most states with a qualifying-condition list, and epilepsy or seizures appear on many of those lists. Rules differ by state: age limits, physician certification, caregiver requirements, THC purchase caps, and possession limits. A state medical card does not replace an Epidiolex prescription.

Questions for your neurologist

  1. Do I have a syndrome that Epidiolex is approved to treat?
  2. What is my weight-based dose range, and how is titration scheduled?
  3. Which of my current medicines interact with CBD?
  4. When are liver enzyme tests checked?
  5. Will my other antiseizure drugs stay the same?

Bottom line

Prescription CBD has trial data and FDA approval for three epilepsy syndromes. Retail cannabis does not. Seizure control is a medical matter that needs a specialist. Do not change or stop antiseizure drugs without a neurologist.