by Philip Ritchie, University of Sydney
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New research shows Australian health care practitioners are often prescribing medicinal cannabis for psychiatric conditions where the evidence for effectiveness is unclear.
But researchers at the University of Sydney who delved into the prescription data say the behavior of these doctors has the potential to unlock avenues of new research.
Their findings are published in Frontiers in Pharmacology, led by Dr. Elizabeth Cairns from the Lambert Initiative for Cannabinoid Therapeutics at the Brain and Mind Center, a world leader in cannabis and cannabinoid research.
"These data confirm many Australians have unmet needs around their mental health and that medicinal cannabis is now frequently being trialed as an alternative to conventional therapies," Dr. Cairns said.
"Medicinal cannabis is not typically prescribed as a first-line therapy, so those using it for conditions such as anxiety and depression likely have not had success with other treatments.
"This provides us with new leads for our clinical trials that will hopefully produce high-quality evidence to support or discourage current patterns of use."
Dr. Cairns and colleagues analyzed the complete record of medicinal cannabis prescribed through Special Access Scheme B (SAS-B), using data supplied by the Australian Therapeutic Goods Administration (TGA) going back to the drug's legalization in 2016, which allowed a diverse range of CBD and THC products to be legally available for medical use.
Prescriptions through this scheme have been increasing annually since the drug made its way into Australia's pharmaceutical market in late 2016. From February 2021 the number of prescriptions started to boom, leaping from 100,000 to 300,000 by September the following year.
After treatment for chronic pain, analysis by the Lambert researchers shows anxiety is the second most common condition being treated with prescribed medicinal cannabis in Australia. However, evidence for the effectiveness of medicinal cannabis products in treating anxiety is surprisingly poor.
There is also increasing prescribing for conditions such as depression, ADHD and autism where an "evidence gap" exists around effectiveness.
Psychiatric prescriptions, used to treat mental, emotional, developmental and behavioral disorders, make up 33.8% of total approvals.
"Despite prescribing for a variety of different psychiatric indications, there is limited published high-quality evidence of efficacy to support this prescribing," Dr. Cairns said.
"The key here is not that the evidence shows cannabis products don't work, more that high-quality studies supporting current prescribing just haven't been done."
Medicinal cannabis has been approved for anxiety disorders far more than any other psychiatric condition, making up 22.6% of all SAS-B prescriptions, and the type of medications used to treat anxiety caught the interest of scientists at Lambert.
"The anxiety data are really interesting because more than three quarters of the products prescribed contain THC (tetrahydrocannabinol), but THC is often thought of as anxiety-inducing, with cannabis use sometimes associated with paranoia and social anxiety," Dr. Cairns said.
"It makes you think, is there something about THC that we've missed historically?
"At the Lambert Initiative, we can examine these issues in a variety of ways because we have the whole range of pre-clinical and clinical researchers, something that is unique in university-based research."
Dr. Cairns suggested more priority research funding is needed to examine the effectiveness of medicinal cannabis products at improving mental health and quality of life.
The researchers said healthcare professionals often struggle to find reliable information about prescribing the hundreds of medicinal cannabis products available, and whether THC or CBD products are best used for different psychiatric conditions.