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• Posted September 11, 2025

High THC Levels May Affect Egg Quality and Fertility, New Study Finds

High levels of THC — the compound in marijuana that causes a “high” — may affect how eggs develop and could lead to fertility problems, miscarriages and chromosome issues in embryos, new research shows.

The findings were reported Sept. 9 in the journal Nature Communications.

Researchers analyzed more than 1,000 samples of ovarian fluid from patients undergoing fertility treatment. They compared unfertilized eggs (oocytes) from 62 women who tested positive for THC with a control group who did not use cannabis.

The study found that women with detectable levels of THC had a higher egg maturation rate. But they also produced fewer embryos with the correct number of chromosomes.

“Chromosomes need time to align perfectly to be ready to be fertilized by sperm and create healthy embryos,” Cyntia Duval, who led the study as a postdoctoral fellow at the University of Toronto, told CNN. “So yes, we have more oocytes that are mature, but at what price if they don’t have the right number of chromosomes?”

The immature eggs were donated by women undergoing fertility treatment and were not suitable for use, Duval said.

When the eggs were exposed to THC in a lab for 24 hours, researchers found more altered spindles — structural issues that affect chromosomes. These changes can interfere with healthy embryo development.

However, Duval noted that the study can't prove cause and effect.

“This is a hypothesis, and the worst thing I would want is for the public to read this and become fearful,” she told CNN. “More studies are needed to verify our findings and determine how or even if the changes we observed affect reproduction.”

The findings dovetail with a rise in marijuana use during pregnancy. A June study found that past-month cannabis use among pregnant women more than tripled in the U.S. between 2002 and 2020.

“The findings of this study are concerning and highlight the importance of a cautious approach in using cannabis when planning to conceive,” Dr. Jamie Lo, an obstetrician and associate professor at Oregon Health & Science University in Portland, told CNN.

She added in an email that the results could support a harm-reduction strategy.

“With this information, these patients can consider reducing the amount of cannabis that they are using to mitigate adverse outcomes to their babies," Lo explained.

THC potency has quadrupled between 1995 and 2022, with some cannabis concentrates reaching 40% THC or higher, according to the National Institute on Drug Abuse.

"Higher THC concentrations have been associated with a greater likelihood of cannabis use progressing to cannabis use disorder, among other health concerns," the Institute’s website says.

As such, Lo offered a cautionary note.

"Because it’s hard to know the specific level of THC in various cannabis products on the shelves, I advise my patients to consider safer alternatives to treat the symptoms they’re using cannabis for or at least try to reduce the frequency of their use," Lo said.

More information

The American Academy of Family Physicians has more on cannabis use during pregnancy.

SOURCE: CNN, Sept. 9, 2025