A new study has found the first direct evidence that cannabis use can cause chromosome errors in human embryos, with women who had detectable tetrahydrocannabinol (THC) levels showing a 9 percent increase in genetically abnormal embryos during fertility treatments.
The research, published in Nature Communications, analyzed more than 1,000 women undergoing in vitro fertilization (IVF) treatment and provides insights into how marijuana affects female fertility at the cellular level as cannabis use among women of reproductive age continues to rise.
The study, conducted by Cyntia Duval, a clinical embryologist at CReATe Fertility Centre and lead author, was based on two studies carried out by her team in Toronto.
In the first study, researchers exposed immature human egg cells to THC, the psychoactive component of cannabis, for 24 hours. The exposed eggs showed a 9 percent higher rate of chromosomal errors and a greater frequency of spindle abnormalities (errors in the cell structures that separate chromosomes), both linked to IVF failures.
In the second study, the team analyzed samples from women undergoing IVF treatment, more than 60 of which tested positive for THC.
“[Cannabis] can also reduce egg quality and increase time to conception, and decrease success with in vitro fertilization,” Dr. Trisha Shah, an endocrinologist and fertility doctor at Conceptions Florida who was not involved in the study, told The Epoch Times.
In the second study, only 60 percent of embryos in the THC-positive group showed the correct number of chromosomes, compared with 67 percent of embryos in the THC-negative group.
“Cannabis intake might be associated with a higher rate of aneuploidy [having an incorrect number of chromosomes] in oocytes [eggs] and embryos, especially for patients undergoing IVF treatments,” Duval told The Epoch Times.
She noted that these chromosomal errors could be associated with lower implantation rates in IVF or a higher risk of miscarriage, although the study was not designed to measure pregnancy outcomes directly. Researchers also did not measure drug use frequency or dosage in IVF patients, meaning that they lacked exact information on cannabis intake.
“We do not know their consumption habits and if they are chronic users or not,” Duval said, noting that this is a factor that will change the distribution, elimination, and overall THC levels found in the body.
The researchers also acknowledged that the study was conducted in the lab and did not examine effects within the human body or account for patient age, which is known to influence egg quality.
The findings come as marijuana use during pregnancy has more than tripled from 2002 to 2020 among U.S. women, with those aged 19 to 30 now using cannabis at higher rates than men. This trend coincides with broader fertility challenges, as birth rates continue declining across developed nations.
Previous research has already linked cannabis use during pregnancy to autism, low birth weight, premature birth, and stillbirth. Studies have also shown that marijuana reduces male fertility, with one finding a 28 percent reduction in sperm count and concentration among users.
Dr. Tiao-Virirak Kattygnarath, an OB-GYN and fertility expert at CARE Fertility and Women’s Health in Toronto who was not involved in the study, told The Epoch Times that the research reinforces existing recommendations. He said cannabis use may interfere with ovulation, hormone balance, and how the uterus prepares for pregnancy.
“Women who use cannabis may take longer to conceive,” Kattygnarath said. “The safest approach is to avoid cannabis when trying to get pregnant.”
He advised that women who use cannabis recreationally stop before trying to conceive and during pregnancy and breastfeeding.
“Even small or occasional use can lower the chances of pregnancy per cycle,” Kattygnarath said. “If cannabis is used for medical reasons, it is best to discuss safer alternatives with a doctor.”
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