Follicular fluid samples from more than 1059 IVF patients were analysed, of which 62 tested positive for THC metabolites (the product of metabolism).
The researchers found an association between higher THC levels and rates of embryos with incorrect chromosome numbers. They compared and supported their finding with independent lab experiments in which immature donor eggs were exposed to THC and had similar abnormalities.
They recommended patients be advised about potential risks of cannabis consumption, and said the research provided the groundwork for regulatory bodies to establish new guidelines.
The effects on sperm of THC, one of the main active compounds in medicinal cannabis products, have been well researched. It has been found to reduce sperm count, concentration, motility (movement) and structure.
But the latest study is the first into THC’s effect on the human egg and ovarian follicle.
AMA president Dr Danielle McMullen said it was encouraging to see research into THC’s effect on female reproduction.
“My takeaway from this paper is that it shows the use of cannabis or things containing it, either recreational or prescribed, may impact aspects of [women’s] fertility,” she said. “It’s yet another reason why it’s really important to visit your GP when planning a pregnancy and get advice on how to optimise your health before trying to fall pregnant.”
Lead researcher Dr Cyntia Duval told CNN that the study could only show an association between THC exposure and egg damage, not a direct cause and effect, and that she did not want the public to become fearful.
“More studies are needed to verify our findings and determine how or even if the changes we observed affect reproduction,” she said.
Dr Polyakov said an important finding was that levels of THC in the blood of patients whose samples were analysed were the same as those in follicular fluid, meaning all eggs were exposed to equal concentration. Because higher levels of THC suggested eggs were more likely to have their chromosome distribution disrupted, it could raise the miscarriage risk of younger women to that of older women.
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Two medicinal cannabis products are licensed by the Therapeutic Goods Administration: one to treat spasticity in multiple sclerosis, and the other for severe epilepsy syndromes in children. But medicinal cannabis is also promoted as an anxiety treatment.
Most products in a local industry estimated at $445.6 million are unapproved and require medical practitioners to prescribe them using clinical justification. The industry is under scrutiny because of a surge in prescribing raising concerns about profit-driven models, aggressive marketing and patient safety.
The Australian Health Practitioner Regulation Agency is cracking down on unsafe practices and misleading advertising by telehealth companies. The TGA is reviewing the Special Access Scheme regulations.
With off-label prescription booming, University of Western Sydney research found in 2020 that one in 10 women with endometriosis pain used medicinal cannabis to self-manage symptoms.
Clinical data is lacking, but the compound is anecdotally linked with reduced pelvic pain caused by chronic gynaecological disorders.
The president-elect of the Royal Australian and New Zealand College of Obstetricians and Gynaecologists, Dr Nisha Khot, said the Canadian study was a great addition to knowledge about cannabis and fertility.
“My advice to women trying to conceive is always a zero approach to alcohol, nicotine, cannabis or any other substances,” she said, “[while] acknowledging the barriers women face to achieving this.”
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