Cannabis may cause defects in human egg cells, study suggests

Cannabis use may affect women’s fertility by causing defects in egg cells, according to new research in IVF patients.

The study examined samples from women undergoing IVF in Canada. Samples that tested positive for tetrahydrocannabinol (THC) – the psychoactive compound in cannabis – showed poorer outcomes.

Researchers in Canada and Israel analysed 1,059 samples of follicular fluid, the liquid in ovaries that surrounds and nourishes developing eggs.

Sixty-two samples tested positive for THC metabolites, showing cannabis use.

These THC-positive samples had fewer embryos with a normal number of chromosomes. Chromosome abnormalities are linked to miscarriage, implantation failure and conditions incompatible with life.

The team also tested immature egg cells from 24 donors to mimic THC effects. At concentrations similar to those found in patient samples, THC was more likely to cause errors in chromosome distribution, raising the risk of IVF failure.

The egg maturation rate – the proportion of eggs that developed ready for fertilisation – was also affected, but only at higher THC levels than typically found in patients.

Cyntia Duval, the study’s lead author and director of translational research at Toronto-based CReATe Fertility Centre, said measuring THC directly rather than relying on self-reporting was a strength.

Duval told Euronews Health: “Our method gives us a much more accurate picture and helped us figure out the exact concentrations to use for our in vitro experiments.”

She noted many women do not disclose cannabis use in self-reported studies.

The authors cautioned their findings apply only to a specific type of immature egg cell.

The study also did not account for other factors, such as age, that influence egg quality.

Duval said it was not clear how often or how much cannabis the women used.

Previous studies have linked cannabis to poorer sperm quality and suggested wider effects on fertility.

More research is needed to confirm how cannabis affects pregnancy outcomes through the pathways identified here.

The researchers stressed that because cannabis use is common, understanding its impact on reproductive health is important for patient care.

Duval said: “Our main goal is simple: to educate people with ovaries and IVF patients that cannabis might impact oocyte maturation and IVF outcomes.

“As cannabis becomes legal in more places, people need access to this kind of information now more than ever.”