There are currently three cannabinoids available on the pharmaceutical market. Dronabinol and Nabilone are both synthetic tetrahydrocannabinol (THC) which the FDA has approved for treatment of chemotherapy-induced nausea and vomiting (CINV) after the failure of a trial of first-line anti-emetics. Both are also FDA approved to treat anorexia associated with AIDS. Recently, the FDA has also approved a cannabidiol (CBD) product to treat seizures associated with Lennox-Gastaut Syndrome and Dravel Syndrome in pediatric patients. However, there is no FDA approved indication for its use as an anti-emetic. Independently produced cannabidiol extracts are being used increasingly in the general population for many non-FDA approved indications, frequently including nausea and emesis. In states that have decriminalized marijuana, both in recreational and medicinal contexts, products with varying ratios of cannabidiol and THC are also used for their anti-emetic properties.
Cannabinoids and their anti-emetic potential are still under research, and many of the intricacies behind their mechanisms are still unknown or lack universal consensus. Cannabinoids exert their anti-emetic properties through interactions with the centrally located CB1receptors and 5-HT3 receptors in the dorsal vagal complex (DVC), which mediates emesis. A significant contributor to emesis is believed to be via activation of 5-HT3 receptors in the DVC, specifically in the area postrema. Studies in animal models have shown that anandamide, an endogenous cannabinoid, THC, and several synthetic cannabinoids have been shown to have allosteric inhibitor effects on the 5-HT3 receptors in the DVC, providing a mechanism through which emesis control occurs. Animal models have also shown that cannabinoids may work on pre-synaptic CB1to decrease the release of serotonin into the synapse, thus inhibiting the nausea/emesis response.
Animal models have also indicated CBD to have an allosteric inhibitory effect on the 5-HT3 receptor. However, this effect is thought to be largely through its activation of the 5-HT1A receptor. Through activation of the 5-HT1A receptor, there is ultimately a reduction in the amount of serotonin released, and thus a lower potential to trigger emesis. CBD is also thought to activate the CB1 receptors in the gastrointestinal tract, through their G-protein-coupled receptor inhibitory effect, leading to decreased gastrointestinal motility. THC and CBD were once credited with inhibiting fatty acid amide hydrolase (FAAH), leading to an increased concentration of anandamide that could exert its anti-emetic properties at a higher intensity, but recent studies into this mechanism have been equivocal.
Dronabinol can be dosed in both oral pill and oral solution form, available in doses of 2.5 mg, 5 mg, and 10 mg. In CINV, the patients should be instructed to take it 1-3 hours before starting their chemotherapy session, with a repeat dose available 2-4 hours after beginning the session as needed. Nabilone is available in oral pill form, in doses of 1 mg or 2 mg. These doses can be increased or decreased based on practitioner discretion. Patients should be instructed to take one dose the night before starting their chemotherapy session, one dose twice a day during the entirety of the chemotherapy course, and one dose twice a day after chemotherapy has concluded. CBD is sold legally throughout the entire United States without a prescription by many private entities that are not FDA regulated; there are no concrete guidelines in dosing. However, doses generally range from 10 mg to 50 mg at a time, taken either as needed or daily. Products containing significant levels of THC are sold legally by medicinal and recreational dispensaries in several states, depending on legal status. Doses for these generally range between 5 mg and 15 mg and are typically taken as needed as opposed to daily, due to their psychotropic effects.
Adverse effects depend on the cannabinoid administered. The most common adverse effects of formulas containing a THC component are acute intoxication, tachycardia, aboulia, and psychosis. Psychoses manifest most commonly as perceptual alteration, but also frequently include panic attacks, anxiety, paranoia, and depression. Individuals using THC containing cannabinoid products chronically and at a high volume are also at risk of developing cannabis hyperemesis syndrome, which can present as intractable nausea and vomiting. Cannabinoid formulas containing only a CBD component have less potential to cause behavioral side effects, although drowsiness occurs frequently. CBD is a CYP3A4 inhibitor, which can lead to drug interactions and toxicities in molecules metabolized by the CYP3A4 system. In vitro studies have shown an association between CBD and reduced fertility and alterations of cell viability. Dronabinol has reported adverse effects including gastrointestinal upset, dizziness, paranoia, somnolence, and abnormal thoughts. Nabilone has reported adverse effects including acute intoxication, ataxia, headache, drowsiness, and deficits to concentration.
Cannabinoids are contraindicated in individuals with a history of hypersensitivity reactions that can be related to any form of cannabinoid consumption. They should be used cautiously in patients who have experienced intolerable side effects in the past. Dronabinol is specifically contraindicated in patients with hypersensitivity to sesame oil.
Monitoring depends on the clinical manifestation of the patient as there are no streamlined laboratory procedures that can measure cannabinoid serum levels. Monitoring of patients receiving cannabinoids should include checking for tachycardia, orthostasis, and behavioral changes. Use by patients with a history of cannabis use disorder should undergo close scrutiny, as the potential of cannabinoid use disorder relapse in such individuals is high. Precautions in patients with hepatic or renal dysfunction are as yet not investigated. Coadministration with CYP inhibitors may lead to toxicity and with CYP inducers may lead to lower efficacy.
There is not much data on the toxicities of cannabinoids in the literature. The lethal dose 50 (LD50) is as yet undetermined, and both dog and monkey models have shown that doses up to 3000 mg/kg do not lead to fatality. There is no antidote, only supportive therapy can be provided in cannabinoid overdose. Chronic, prolonged, high volume use of cannabinoids can lead to neuropsychiatric effects with IQ and cognition being most impacted. The toxic dose reported for dronabinol is estimated to be at 30 mg/kg. Illicit synthetic cannabinoids are known to lead to toxicity at much lower doses.
Opinions and values regarding cannabinoids in medicine vary by the individual and can range from seeing great potential to ease suffering to believing molecules derived from cannabis have no place in modern medicine. Regardless of personal values, healthcare providers should recognize the existence and use of cannabinoids among their patient population, and take this in to account when deciding on treatment options. Patients should feel comfortable telling their provider if and how they use cannabinoids, and the type (CBD:THC ratio). Dronabinol and nabilone are both legal throughout and are available by prescription in all 50 states. The legality regarding formulas that contain only CBD is more variable. (These products are available legally throughout all 50 states.) Laws are much more variable between the states with regard to restricting products with THC components. If a patient reports to the medical staff they are using a cannabinoid, that information should ultimately be relayed to the primary physician overseeing their care.
The primary specialties that are prescribing dronabinol and nabilone are oncology, palliative care, and infectious diseases. Oncology providers will often order for simultaneous treatment with a cannabinoid alongside chemotherapy regimens. Palliative care and infectious diseases providers will often order cannabinoids to provide comfort in the setting of nausea or to capitalize on their orexigenic components. Providers from varying specialties can order permission for patients with a variety of ailments, including nausea and vomiting, to obtain and use CBD and THC containing formulas in states with legal, medical marijuana. Providers from many specialties have also recommended over-the-counter CBD-only products to their patients for numerous indications, also including nausea and vomiting. The research behind the potential of cannabinoids in medicine is still in its initial phases, and much of the biomedical applications researched are reliant on recent animal models and anecdotal cases. It is essential to take the entire clinical picture into account when deciding whether to initiate cannabinoid therapy.