In June 2018, the US Food and Drug Administration (FDA) approved Epidiolex, or cannabidiol (CBD), for the treatment of Dravet syndrome and Lennox-Gastaut syndrome, two childhood epilepsies. Even though the drug is now legal, not all patients may be eligible for it. Epidiolex is approved for only those two conditions, and insurance companies may not cover its use in other epilepsies.

Because of this, some patients may consider purchasing CBD from a dispensary, says Orrin Devinsky, MD, FAAN, director of the New York University Comprehensive Epilepsy Center and a lead investigator in ongoing trials of Epidiolex. But Dr. Devinsky cautions that many uncertainties remain about products available through dispensaries.

Differences in Grade

Marijuana sold through dispensaries is not the same as pharmaceutical-grade CBD, says Barry Gidal, PharmD, professor of pharmacy at the University of Wisconsin School of Pharmacy in Madison.

 The CBD in Epidiolex is extracted and manufactured in a controlled and precise environment, ensuring consistent purity and potency.

Lack of Oversight

Currently, no national standards or oversight exist for purity or potency of other types of medical marijuana, so patients and families can’t be sure they’re getting what the label describes. As with any drug, dosing is very important. Doctors often calculate the dosage based on the patient’s weight. But if a dispensary can’t be sure of the precise strength of a compound, it can be difficult to calculate the right dosage.

 Because the botany is so complex, the amount of CBD in a particular plant or part of a plant varies with soil conditions, light, water, and even how close plants are to one another. Extracting precise amounts of CBD and producing consistent batches require a controlled environment and oversight most medical-marijuana producers may not have. Even with dispensaries and producers that may have mastered the process, not enough oversight or data exist to say for certain which products are pure and consistent.

Inconsistent Purity

Consumers can’t be sure dispensary marijuana doesn’t contain THC, pesticides, or other contaminants, says Shlomo Shinnar, MD, PhD, FAAN, professor of neurology at Montefiore Medical Center and the Albert Einstein College of Medicine in New York and president of the American Epilepsy Society. FDA-approved Epidiolex, on the other hand, is a pharmaceutical-grade form of CBD of known purity and strength, he says. That means doctors can be confident of what they are prescribing and patients certain of what they are getting.

Higher Costs

Another potential obstacle to using dispensary marijuana is cost, says Elaine C. Wirrell, MD, FAAN, director of pediatric epilepsy at Mayo Clinic in Rochester, MN. The dosages that worked best in the Epidiolex trials were high compared with the potency available through dispensaries, she says. To purchase the correct dosage through a dispensary could cost as much as $1,000 a month, and insurance companies are unlikely to cover it.

Learn more about cannabidiol and whether it can be used to treat other disorders.