Exploring the Truth
[dropcap class=”kp-dropcap”]S[/dropcap]cience has long indicated that when it comes to fertility, cannabis may not be your friend. Studies on animals have suggested that when it comes to reproduction for both males and females, cannabis has damaging effects—but when it comes to studies on humans, the research is less consistent. Most of the existing research indicates that consuming cannabis may not be a wise choice if you’re struggling to conceive a baby.
A recent study challenges this body of knowledge, however. The Boston University study, called “Marijuana use and fecundability in a North American preconception cohort study,” headed by Dr. Lauren A. Wise came out in December 2017. Unlike previous studies, this one’s findings suggest that cannabis has essentially no effects on fertility, negative or otherwise. Despite her extremely busy schedule, Dr. Wise made time to answer some questions for CULTURE about her recent findings, and how they relate to existing research on this subject.
“In humans, some studies of men report that chronic marijuana use in men is associated with lower testosterone and LH levels and poor semen quality, but many studies have not confirmed these findings, and reversible effects have been observed five to six weeks after initiation.”
Were you surprised at your initial findings that indicate cannabis seemed to have an essentially benign impact on fertility?
Dr. Wise: Yes, we were somewhat surprised. Animal studies have reported adverse effects of the active ingredient marijuana on reproductive hormones and sperm morphology. Studies among humans have also suggested adverse effects of marijuana use on reproductive hormones (both sexes), ovulation and semen quality, but results have been less consistent. And some studies indicate that humans may develop tolerance to the adverse reproductive effects of marijuana over time. So, we went into this thinking we would find an adverse effect of marijuana use on fertility for both females and males.
Where did the previous belief that cannabis lowered sperm count come from? Were there previous studies that supported this or is it basically just a myth?
No, it is not a myth. Several animal studies have shown inhibition of Leydig cell function, reductions in testosterone, gonadotropins and testicular size and abnormal sperm morphology following acute exposure to the active ingredient in marijuana, delta-9-tetrahydrocannabinol (?9-THC). In humans, some studies of men report that chronic marijuana use in men is associated with lower testosterone and LH levels and poor semen quality, but many studies have not confirmed these findings, and reversible effects have been observed five to six weeks after initiation. A large population-based Danish study actually reported an increase in testosterone levels among recent marijuana smokers (which we would expect to be associated with better semen quality). So the results are somewhat mixed even for semen quality. It was a strength that we studied fecundability directly, instead of semen quality (a more indirect measure of fertility), because several studies have shown that poor semen quality is only weakly associated with fecundability.
How does cannabis affect female fertility?
In our paper, we summarized the research on cannabis and females as follows: “In female animals ranging from rodents to non-human primates, delta-9-tetrahydrocannabinol (?9-THC), the active ingredient in marijuana, has been associated with reduced gonadotropin levels (via suppression of luteinizing hormone (LH) pulsatile secretion), disrupted ovulation and menstrual irregularities. However, in one study of primates, normal menses returned after 3–4 months of chronic exposure. In women, studies are more conflicting. One study found a 30 percent decrease in LH levels among marijuana smokers in the luteal phase, but little effect in the follicular phase. In another study, exposure in the periovulatory stage was associated with increased LH levels. While intensive marijuana smoking was associated with normal menses in one study, other studies have shown increased anovulation, longer follicular phases and shorter luteal phases. Finally, recent marijuana use has been associated with reduced oocyte retrieval and fertilization among couples undergoing in vitro fertilization and an increased risk of ovulatory infertility.”
“The extent to which our results were influenced by mis-reporting of marijuana use is unclear.”
Where do you see the future when it comes to cannabis and fertility?
More research is needed to see whether a consistent finding of no effect emerges from other studies of marijuana use and fertility. The extent to which our results were influenced by mis-reporting of marijuana use is unclear. Future studies with day-specific data on marijuana use might better be able to distinguish acute from chronic effects of marijuana use, and evaluate whether effects depend on other factors, such as marijuana dose, mode of ingestion, duration and recency of use, and timing of use relative to phase of menstrual cycle.
As Dr. Wise stated, more research must be done on this fascinating subject before there are any definitive answers one way or the other. Still, it’s encouraging to hear that with more research, there is a possibility we may find evidence to support what many cannabis users likely already believed—of all the substances that may impact your ability to reproduce, cannabis is pretty low on the list.
