Does cannabis affect your fertility?
While there are a lot of unknowns about marijuana use and fertility, researchers think it's important for patients to know the risks.
For many women, fertility can be a frustrating and stressful journey filled with unanswered questions. Some turn to cannabis to help deal with the stress, but now, a new study hints that the drug might actually make fertility issues worse.
“Some people might think that it's a plant, so therefore it's natural, therefore it might not be as risky as other drugs,” says Cyntia Duval, a clinical embryologist at a Toronto clinic called CReATE Fertility Centre and lead author of the study. “I think people with ovaries need to know how it can potentially affect their oocytes”—the technical term for immature egg cells.
Published September 9 in Nature Communications, the study is among the first to examine cannabis and female fertility. It’s still unclear how this could play out in the body, whether different forms of cannabis present different risks, and how the drug compares to more established risky substances like alcohol.
(How does cannabis affect the body?)
Linking THC with fertility red flags in IVF
Duval’s team studied in vitro fertilization (IVF) patients—both people donating eggs and retrieving their own eggs. The team used byproducts of the process to understand how the process of oocytes maturing changes in the presence of tetrahydrocannabinol, known commonly as THC. It’s the primary psychoactive cannabis compound or cannabinoid in marijuana and creates the high associated with the drug.
First, the team looked at follicular fluid, which surrounds oocytes. The higher the concentration of THC—and the products it breaks down into, known as its metabolites—found in a patient’s follicular fluid, the faster the oocytes matured.
To become an egg, all oocytes must mature, but disrupting the normal rate of this delicate process can cause the eggs to develop incorrectly: Fewer embryos developed with the correct number of chromosomes when the eggs came from people with THC in their follicular fluid. Such embryos are rarely implanted during IVF. If they are, they often result in a miscarriage or a stillbirth.
Duval and her colleagues also looked directly at immature oocytes, which are often discarded during the IVF process. Exposing the oocytes to THC at both average and high levels seen in participants produced similar results: Chromosomes were again less likely to properly divide.
Still, it’s impossible to directly link THC to maturation rate issues. Though many participants were donors and younger, some IVF patients were older, which could also impact maturation rates—something the researchers could take into account for the follicular fluid experiment but not the oocyte lab tests.
The results don’t mean women can’t get pregnant while using cannabis, Duval says. “If the ‘70s showed us something, it’s that you can get pregnant by being high,” she says. “That's not a question. It’s really how [cannabis] can impact the human oocyte by itself. It’s one of the most precious and unique cells in the body and the hardest to study, in my opinion.”
What we know about cannabis and fertility
Despite its limitations, the study adds to a field plagued by limited data. Very few studies have been done on oocyte responses to cannabis, and even fewer focused on human oocytes. Other studies on cow and mice oocytes have yielded mixed results, although they didn’t study metabolites of THC in addition to the compound itself.
In studies of male fertility alongside THC use, the results are similar: Cannabis users were less fertile. In one study, men who reported smoking marijuana more than once a week had a 29 percent decrease in sperm count compared to those who didn’t. In other studies, marijuana users also had an increased count of abnormally shaped sperm.
“I was able to find a lot of information about the impact of cannabis on male fertility, the impact of cannabis on pregnancy, but almost nothing, or only in animal models, on the impact of cannabis on female fertility,” Duval says.
Part of the reason why more studies exist on THC and male fertility is that it’s simply easier to study. Even though men have just slightly lower infertility rates compared to women in the United States, the process of testing sperm is far less invasive than obtaining an oocyte.
(These recent scientific findings change what we know about cannabis.)
Why is it so hard to study cannabis and female fertility?
With humans involved in a study like this, the ethical concerns are higher, which is why everything used in this study was a byproduct of elective IVF that would have been discarded otherwise.
While IVF provides a venue to study cannabis and fertility, it alone is an intense process, and getting participants to sign up for a research study on top of that is a big ask. “You have to go through this IVF process and ovarian stimulation and then oocyte retrieval. It's a needle across the vaginal wall, and they have to puncture the ovaries to get access to the follicular fluid and the oocyte,” says Duval. “It's much more invasive than the male counterpart.”
Marijuana’s status as a federally illegal drug also makes research like this harder to conduct, and people may be reluctant to share drug use. “I think especially in pregnancy, there's a high social desirability to not use any substances, and so patients are much less willing to disclose use in any setting,” says Torri Metz, a maternal fetal medicine physician at University of Utah Health who was not involved in the study.
And, in around half of U.S. states, healthcare professionals are required to report prenatal substance use. “Many pregnant patients fear the consequences of truthful reporting of prenatal substance use to their healthcare providers,” says Qiana L. Brown, an epidemiologist at Rutgers University who was not involved in the study. “While state laws and associated policies on this issue vary widely, being reported for prenatal substance use can result in separation of mother and baby shortly after birth if the baby has been exposed to substances in utero,” she says.
In the IVF analysis, 73 percent of participants who tested positive for THC and its metabolites did not report cannabis use when completing their patient intake questionnaire. Testing follicular fluid gave researchers an accurate assessment of marijuana use, but in many cases, researchers rely on self-reporting, which can often be inaccurate.
(Scientists are finally studying women’s bodies. This is what we’re learning.)
How could cannabis disrupt fertilization and pregnancy?
The human body produces its own cannabinoids, and they trigger a network of signals and receptors that manage essential functions like emotional processing, sleep, and memory. During conception and throughout a pregnancy, this system is especially active and helps with embryo transport and placenta implantation.
So, when someone consumes THC, it hijacks this system, binding to receptors and altering things like memory and appetite. “Whenever you have a pathway that has receptors in the body to do something specific, and then you interrupt it by bringing in cannabis that can interact with those receptors in an unanticipated way and potentially disrupt those natural processes, that's when we worry about these adverse effects,” Metz says.
But we don’t know the exact mechanisms of THC in potential fertility issues, nor do we know how different consumption of the substance—whether through smoke or edible products—may impact oocytes.
Still, “we know that cannabis affects sperm. We know that cannabis affects the pregnancy, and now this study really demonstrates that it also affects the oocytes and fertility,” Metz says.
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How cannabis fits in with other risks is unknown
Some people turn to cannabis to remedy nausea and pain symptoms that can come with IVF and pregnancy—though it’s unclear how well it works compared to alternatives, and could even exacerbate nausea, says Ilina Pluym, a maternal fetal medicine physician at UCLA who was not involved in the study.
“There's a lot of misinformation and marketing that people say it will help your nausea. I actually see the opposite,” Pluym says. “There's certainly other medications that are safer that we can use to treat their nausea, to treat their anxiety, to treat their sleep.”
And, because THC can take several weeks to dissipate in the body, the best thing to do is to avoid it altogether if you’re trying to get pregnant, actively pregnant, or breastfeeding, Pluym says.
There are still a lot of unanswered questions about how marijuana may impact fertility, pregnant people, and fetal development, especially when compared to other drugs like alcohol, which have named syndromes for their effects. “We're really in relative infancy in the field in terms of cannabis exposure and what those health risks are,” Metz says.
The lack of research on marijuana compared to these other substances doesn’t mean it’s less dangerous, even if it becomes legal in more states. “I think that it’s maybe not perceived as harmful as tobacco, as alcohol, even though it can be,” Pluym says. “Just because it’s legal, doesn’t mean it’s safe.”
