Chemotherapy is a necessary treatment for many cancers, but it often comes with a distressing side effect: chemotherapy-induced nausea and vomiting (CINV). This not only drastically impacts a patient’s quality of life but in some cases can also lead them to stop treatment altogether. Even with current medications, about a third of patients taking chemotherapies which are moderately associated with causing nausea and vomiting, still experience symptoms.
Alternative therapies are still therefore needed to effectively mitigate nausea and vomiting related to chemotherapy.
What about medical cannabis?
CINV is mediated by several pathways linked to serotonin, dopamine, substance P, and cannabinoid receptors. Past studies have focused on the role of the Cannabinoid 1 (CB1) receptor in CINV, and have found that administration of THC and synthetic cannabinoids (e.g., nabilone), may be associated with improvements in CINV. However, these treatments were also associated with dose-dependent side effects such as dizziness, sedation, and anxiety.
In addition to having anxiolytic properties, some evidence indicates that CBD may be able to reduce some of the neuropsychiatric effects of THC. Administering both cannabinoids may therefore help to reduce the risk of side effects associated with THC alone.
The way CINV works involves several pathways in the body, some of which are linked to cannabinoid receptors – the same ones targeted by compounds found in cannabis, such as tetrahydrocannabinol (THC) and cannabidiol (CBD).
There is already a licensed medical cannabis product for CINV called Nabilone. This is a synthetic compound which acts similarly to THC. According to NICE it can be considered by NHS doctors as an add-on treatment when CINV persists despite first-line treatments.
A Closer Look at the Clinical Trial
A recent randomised placebo-controlled trial aimed to assess the effects of an oral cannabis extract containing both CBD and THC in adult patients who experienced severe CINV despite taking standard anti-sickness medication.
The Treatment: Participants received either capsules containing a 1:1 mix of THC (2.5mg) and CBD (2.5mg), or identical-looking placebo capsules. Everyone also continued their usual anti-nausea medication.
The Study Design: The trial had two phases.
- In Phase II, participants first took either the cannabis extract or the placebo, then switched to the other one for the next round of chemotherapy.
- In Phase III, they continued with whichever treatment they had initially been assigned.
What Did the Trial Find?
- Results with Cannabis: The group receiving THC:CBD had a higher rate of ‘complete response’ (no vomiting and no need for additional medication) compared to the placebo group.
- Less Nausea and Vomiting: They also experienced less nausea overall, vomited less frequently, and needed to use ‘rescue’ medication less often.
- Patient Preference: In Phase II, where participants tried both treatments, 83% preferred the cannabis extract over the placebo.
- Side Effects: Side effects were more common with THC:CBD, mainly sedation and dizziness. A few rare side effects like anxiety and hallucinations were also reported.
Conclusions
In the setting of this trial, THC and CBD showed promise as an add-on therapy for patients whose nausea and vomiting aren’t controlled by standard medications. However, this evidence is not sufficient on its own to suggest THC and CBD is an effective treatment for chemotherapy-induced nausea and vomiting. Further trials will be necessary to evaluate this finding further and assess safety.
