New Research Warns of Female Fertility Risks From Marijuana Use

Researchers found that cannabis use may interfere with egg health, raising the risk of failed fertilization or unhealthy embryo.

A worker removes leaves from marijuana plants to allow more light for growth at Essence Vegas's 54,000-sq-ft marijuana cultivation facility on July 6, 2017. Ethan Miller/Getty Images

Exposure to marijuana could affect the health of a woman’s eggs and raise the risk of genetic problems in embryos, a new study suggests.

In a study published on Tuesday in Nature Communications, researchers at a Canadian fertility clinic found that higher levels of tetrahydrocannabinol (THC)—the main compound in cannabis that produces a “high”—may interfere with how eggs mature, possibly leading to chromosomal errors that can cause birth defects.

For their study, the team examined more than 1,000 ovarian fluid samples from women undergoing fertility treatment. Among them, unfertilized eggs from 62 women who tested positive for THC were each compared with two matched controls from women who didn’t use cannabis.

The comparison suggested that eggs exposed to THC tended to mature faster and, as a result, might be less likely to develop into embryos with the correct number of chromosomes. When chromosomes don’t align perfectly, the egg may fail to be fertilized or may form an embryo with defects.

Unfertilized eggs, or oocytes, “need sufficient time to reach cytoplasmic maturity,” the researchers wrote, referring to a stage that marks the completion of all biochemical and structural changes necessary for successful fertilization and the development of healthy embryos. The process depends on the “precise and faithful” packaging of key materials, including the mother’s messenger RNA (mRNA) transcripts, which are the only source of instructions for early embryo growth until the embryo’s own genes become active.

“Taken together, THC exposure seems to impact critical transcripts involved in key oocyte maturation processes, fertilization, early embryo development and implantation,” they concluded, while noting that the specific mechanisms by which THC affects these processes in human oocytes remain unknown.

Another part of the study looked at very immature eggs grown in a test tube in a lab setting. These eggs, donated by women undergoing fertility treatment and not suitable for use, were exposed to THC under controlled conditions.

After 24 hours, the eggs exposed to higher levels of THC showed more defects in their spindles—the tiny structures that guide chromosomes into place during cell division. Such errors could potentially prevent an embryo from developing normally.

“Collectively, this data presents compelling evidence that cannabis consumption may negatively impact female fertility,” the researchers wrote.

The findings add to a growing body of literature on how cannabis affects female reproduction. In May, scientists at Oregon Health & Science University conducted a systematic review of 51 studies involving more than 21 million people. They found that using cannabis during pregnancy was associated with higher risks of preterm birth, low birth weight, and even infant death.

Unlike alcohol and nicotine use, which have declined among pregnant women in recent years, cannabis use has risen as laws and norms around marijuana have relaxed. A June study in the American Journal of Preventive Medicine reported that self-reported cannabis use in the past month more than tripled among pregnant women in the United States between 2002 and 2020.

The impact of cannabis on male fertility has been more extensively studied and better documented. As early as the late 1990s, University at Buffalo researchers found that THC activates the same brain receptors as anandamide, a naturally occurring cannabinoid in the body that can prevent sperm from fertilizing an egg. Heavy users of marijuana, they said, risk jeopardizing fertility by “overloading” this natural signaling system that regulates sperm motility.

Follow-up studies at the university suggested that men who frequently smoke marijuana tend to have lower volumes of seminal fluid, reduced overall sperm counts, and abnormal sperm behavior. In many cases, sperm moved “too fast too early,” burning out before they reached the egg and making fertilization unlikely.

More recent research has reinforced these concerns. A 2020 study of 229 Jamaican men, for instance, found that even moderate cannabis use was linked to a three-and-a-half times greater likelihood of producing misshapen sperm, significantly lowering the chances of successful fertilization.