The cannabis plant contains 554 compounds. These compounds, or active chemicals, include 113 cannabinoids, two of which are tetrahydrocannabinol (THC) and cannabidiol (CBD).

“As we look at pharmacological actions and expected therapeutic responses, a name label is not going to help us, but instead knowing whether it's a THC type, or CBD type, or hybrid type,” said Kari Franson, PharmD, PhD, BCPP, professor and associate dean at the University of Southern California.

Although it's still an area of evolving research, cannabinoids such as THC and CBD are known to have different effects on the body. THC binds to cannabinoid receptors in the body, while CBD may interact indirectly with cannabinoid receptors. THC is the chemical responsible for the psychoactive quality of cannabis, but it also has antinausea and analgesic effects. CBD, which has no psychoactive properties, is said to help with inflammation. Other compounds in the plant, such as the terpenes and flavonoids, may play a synergistic role in the therapeutic effects of cannabis—what's known as the “entourage effect.”

Fiona Oxsher, PhD, cofounder and general manager of LKN Extractions, said that learning about the body's endocannabinoid system—which was only discovered in 2002—helps us understand how cannabinoids work.

The endocannabinoid system controls a person's response to stress, as well as one's mood, appetite, energy balance, and more. In an April 21, 2021, APhA webinar, Oxsher explained that our bodies have been increasingly void of cannabinoids because of our environment, the food we eat, and other factors. Plants with cannabinoids are a way to saturate this system—the CB1 and CB2 receptors, specifically—she said.

Cannabinoids are also present in rosemary, echinacea, kava, and other plants. “But cannabis has the highest percentage of cannabinoids,” said Oxsher.

For most neurological diseases, cannabis can help with symptom management. During her presentation, Faulkner discussed the research on a few neurological conditions outside of epilepsy: multiple sclerosis, Parkinson's disease, and headache disorders.

For example, Parkinson's disease is included in the accepted indications for medical cannabis in 17 states, despite statements from organizations like the American Academy of Neurology that say cannabis does not work for motor symptoms or levodopa-induced dyskinesia in patients with Parkinson's disease.

Most pharmacists are probably familiar with patients inquiring about CBD products.

“Patients are already using [CBD] or will come to pharmacists saying they want to explore it,” said Michael Deme, PharmD, a clinical pharmacist at RxClinic Pharmacy in Charlotte, NC, during the April 21 APhA webinar.

Even though data are lacking on CBD and specific drug interactions, Deme said it's an area where a pharmacist's expertise is needed.

“We do know that CBD is metabolized by the liver with enzymes CYP2C19 and CYP3A4,” said Deme. “Most pharmacists know those are major players in all other drug metabolism.”

To cite just one example, if a patient is using a CBD product and is on carbamazepine, which is a CYP2C19 inducer, the CDB dose might not be as effective for them. “Maybe the patient is not getting any benefits from CBD after being on it for a while. Maybe their dose is too low because they are on an inducer medication.” The opposite can also hold true when a patient is on a CYP2C19 inhibitor, in which CBD might not be metabolized as well and could be causing an adverse effect.

According to Faulkner, there are some known drug interactions with cannabidiol. “In particular, it interacts with several of the other antiepileptic medications that we use for the treatment of these same disorders,” she said.

Faulkner said medication doses for diazepam, clobazam, and stiripentol, for example, will likely need to be reduced to prevent toxicity in patients.

She said it's also worth noting that elevations in liver enzymes seem to occur more readily with coadministration of valproic acids. “This is important to know if you have a family member who is seeking out cannabis for use in a child with seizures who is on some of these conventional therapies without the oversight of a medical practitioner,” Faulkner said.