Short answer

The only cannabis-based medicine the FDA has approved for epilepsy is cannabidiol oral solution, sold under the brand name Epidiolex. Dosing is by body weight, not a fixed milligram amount. The label starts at 2.5 mg per kg two times a day, moves to 5 mg per kg two times a day after one week, and caps at 10 mg per kg two times a day (20 mg per kg per day) for Lennox-Gastaut syndrome and Dravet syndrome. Tuberous sclerosis complex has a higher cap of 12.5 mg per kg two times a day (25 mg per kg per day). The label covers patients age 1 and older.

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Dose steps from the label

  1. Week 1: 2.5 mg/kg two times a day, which is 5 mg/kg per day.
  2. Week 2: 5 mg/kg two times a day, which is 10 mg/kg per day.
  3. Dose increase: the prescriber can raise the dose to 10 mg/kg two times a day if seizures continue and side effects allow.
  4. Ceiling: 20 mg/kg per day for Lennox-Gastaut and Dravet syndromes, 25 mg/kg per day for tuberous sclerosis complex.

Weight changes the pill or milliliter count. A 25 kg child at the starting dose takes 62.5 mg per dose, which is 125 mg per day. The same child at the top Dravet dose takes 250 mg per dose, which is 500 mg per day. A 70 kg adult at the top Dravet dose takes 700 mg per dose, which is 1,400 mg per day.

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Why weight drives the dose

Blood levels of cannabidiol track with milligrams per kilogram, not with a flat amount. Two patients taking the same total milligrams per day can have different blood levels if their weights differ. That is why the label uses mg/kg and why a prescriber records weight at visits. Titration takes two weeks or more. A fast ramp raises the odds of sedation, diarrhea, and liver enzyme spikes. The FDA approved Epidiolex in June 2018 for patients age 2 and older and added tuberous sclerosis complex in 2020. The drug holds a Schedule V slot under federal law.

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Products sold through state programs

State medical cannabis programs sell flower, oil, tincture, and edible products that the FDA has not reviewed. These products contain THC, cannabidiol, or both, and they carry no standard dose. Tests of CBD products sold outside the drug supply have found label amounts that differ from measured content. Neurologists treat these products as unregulated drugs and cannot predict dose from the package. Professional guidance tells patients to report every cannabis product they use, including dose, brand, and batch, at each visit.

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Liver tests

The Epidiolex label calls for blood tests of ALT, AST, and total bilirubin before treatment, then at 1 month, 3 months, 6 months, and within 1 month of any dose change. Enzyme rises happen more in patients who also take valproate. The label advises a lower dose in patients with liver disease. Signs of liver injury include yellow eyes, dark urine, belly pain, and nausea. Patients with these signs should call a doctor.

Drug interactions

Cannabidiol blocks several CYP enzymes. This raises blood levels of some drugs and changes their effect.

  • Clobazam: cannabidiol raises the level of norclobazam, the active metabolite. More sedation and drooling can follow. The prescriber may cut the clobazam dose.
  • Valproate: the pair raises the risk of liver enzyme elevation and of low platelets.
  • Everolimus and tacrolimus: doses may need adjustment when cannabidiol is added.
  • Alcohol and other sedatives: added sleepiness.

Side effects in trials

In the randomized trials that led to approval, cannabidiol lowered monthly seizure counts compared with placebo in Dravet syndrome, Lennox-Gastaut syndrome, and tuberous sclerosis complex. Listed side effects include:

  • Sleepiness and fatigue
  • Diarrhea
  • Decreased appetite
  • Vomiting
  • Liver enzyme elevation
  • Rash, insomnia, and infections in some trials

What the evidence does not cover

Evidence on THC-dominant cannabis for epilepsy is limited, and no accepted mg/kg schedule exists for those products. Whole-plant flower and resin have no standardized cannabinoid content, so a milligram dose cannot be confirmed from the package. Prescribers ask for the exact product, batch, and lab report before they advise a patient. A dose change in an unregulated product is a guess, and seizure control can change with it.

Questions for a prescriber

  • What is my or my child's weight in kilograms?
  • What is the mg/kg dose at each step, and what is the top dose for my diagnosis?
  • When are the liver tests due?
  • Which of my other drugs interact with cannabidiol?
  • Which side effects need a call right away?