Basic information on the pharmacology of medicinal cannabis and its clinical use is lagging behind regulatory changes and public expectations for access to treatment, Australian experts claim.
Professor Jennifer Martin, who is involved in government-funded cannabis trials in Newcastle, and Melbourne addiction specialist Associate Professor Yvonne Bonomo, contrasted the limited evidence base for cannabis products and use with the requirements for conventional pharmaceuticals.
Writing in the Medical Journal of Australia, they said the missing links include data on the indications, efficacy, safety and dose range of cannabinoids.
“Some cannabis products, for example botanical leaf extract, contain more than one cannabinoid, and several cannabinoids metabolise to compounds that may also be active,” they said.
“Other cannabinoids may consist of one molecule only, similar to most current therapeutic goods on the market. How these different molecules and combination of molecules will be handled is unknown at this stage.”
The Newcastle studies are generating some safety and dose-finding data, but only for vaporised leaf cannabis within a tight dose range in patients with cancer cachexia.
More information is needed on starting doses and likely toxic doses in patients across a range of ages and diseases, they said.
However, registration of cannabinoids and widespread uptake could reduce the impetus for further placebo-controlled research.
Other missing links included confirmation that the drug constituents are consistent and of a high quality, confirmation of drug stability in different storage conditions, and specific prescribing information such as the route of administration and duration of treatment.
Medical supply of a potentially “misusable” substance is a particular concern, given experience with medications including oxycodone, benzodiazepines and atypical antipsychotics.
“Restriction of prescribing to specific practitioners, such as palliative care, pain or addiction medicine specialists will be important, especially in the early stages of prescribing
while the clinical experience is accumulating,” they said.
“In Canada, doctors are gatekeepers for the system, but many cite lack of research and guidance from authorities as the reason for declining to prescribe cannabis, even though most support a perceived public health aspect.”
Professors Johnson and Bonoma emphasised the need to separate discussion about medicinal cannabis from the wider debate about legalising the drug for non-medical use.
Regulatory developments in Australia include amendment of Commonwealth narcotic laws in February this year to allow controlled cultivation of cannabis for medicinal or scientific purposes, and a current discussion with the Therapeutic Goods Administration about reclassifying medicinal cannabis from S9 (prohibited drug) to S8 (controlled drug).