Medical Marijuana for Epilepsy: What We Know

Earlier this year, the Virginia State Legislature voted to expand the medical cannabis oil program in the Commonwealth. I have patients ask me about medical marijuana during every clinic visit. Here are a few talking points that will help guide the discussion with your patients.

Patients usually start the conversation by saying, "I read on my cousin's Facebook wall that smoking marijuana can treat my epilepsy."

Let's take a step back and talk about the clinically important compounds in marijuana. The first is tetrahydrocannabinol (THC). It exerts its effect through a pair of G protein-coupled cannabinoid receptors named, conveniently, CB1 and CB2. The effect of THC on synapses produces the typical "high" that allows you to tolerate 11-minute guitar solos and most items on Taco Bell's late-night menu. Early animal models showed mixed effects of THC on epilepsy and, in some cases, worsening seizures. This is different from cannabidiol (CBD), which interacts with a variety of other receptors. More promising effects reported in early animal models and anecdotal evidence from case reports spurred the movement towards clinical trials measuring the effect of CBD on epilepsy.

Will medical marijuana help my epilepsy?

We don't know which epilepsy syndromes are most responsive to CBD. We don't know the long-term effects of CBD or THC in the brains of patients with epilepsy. We have not agreed on the best dosing strategy for these medications. The best evidence for CBD in epilepsy comes from two recently published trials studying the effect of the drug in patients with Lennox-Gastaut syndrome and Dravet syndrome.^[1,2] These diseases develop in childhood or infancy due to underlying genetic changes and are resistant to treatment.

In the studies, patients who were taking an average of six other antiepileptic medications received CBD as an add-on therapy to conventional medications. At 3 months' follow-up, patients who received the CBD experienced a statistically significant decrease in average seizure frequency compared with placebo.

Can I use commercially available CBD?

Unfortunately, many of the products that are available online or over the counter at your local vape shop are not consistent with labeling. Simply put, there's no guarantee that you are getting what's advertised. In addition to unknown dosing and concentrations of THC and CBD, there is a possibility of contaminants, such as pesticides or other drugs, in the product. We can only guarantee the safety and efficacy of US Food and Drug Administration (FDA)-approved products.

How will CBD affect my other medications?

CBD is metabolized by the liver and inhibits cytochrome P450 (CYP) isoenzymes. This inhibition leads to increased levels of topiramate, zonisamide, eslicarbazepine, rufinamide, clobazam, and valproic acid.

Is it legal?

The FDA recently approved a CBD formulation, but there is currently no formulation of CBD that can be prescribed with a Drug Enforcement Administration (DEA) license. Under federal law, cannabis is still considered a Schedule I drug. It is only available through clinical trials and rare compassionate-use exceptions. Patients and providers should familiarize themselves with local laws before recommending CBD for the treatment of epilepsy.

Any views expressed above are the author's own and do not necessarily reflect the views of WebMD or Medscape.

Cite this: Medical Marijuana for Epilepsy: What We Know - Medscape - Jul 26, 2018.

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