Marijuana affecting fertility has been a hotly debated topic for decades now, preceding the push for legalization by decades. Now that researchers can obtain high quality marijuana for experimentation, we are starting to get a clearer picture of its effects on the body. For now, we will look at how marijuana can impact both the male and female reproductive systems.
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Marijuana and the Female Fertility
A fantastic article was recently published by RxLeaf concerning marijuana use and pregnancy. In this article, Philip Ghezelbash points out the confusing and sometimes opposing findings common in burgeoning scientific fields.
The article also points out that marijuana seems to have a pronounced effect on the length of certain parts of the menstrual cycle. One study, for example showed a longer follicular phase correlated with higher self-reported use of marijuana, resulting in a delayed ovulation . A similar result was found in Rhesus monkeys who had been given THC during certain stages in their menstrual cycles .
It is thought that these changes happen due to marijuana’s effects on the hypothalamic-pituitary-ovarian (HPO) axis . Essentially, it is thought that THC suppresses the release of specific hormones, causing downstream effects in the anterior pituitary gland. These chemicals are responsible for promoting follicular maturation and inducing ovulation.
The endocannabinoid system has also been shown to be expressed in several tissues in the female reproductive system; including the ovaries, fallopian tubes, myometrium, and endometrium. Though specific mechanisms are still unknown, it has been shown that the endocannabinoid system is active during folliculogenesis . This means that during the period when the body is producing mature eggs, the endocannabinoid system is actively modulating at least some of the process.
The endocannabinoid system is also highly active after fertilization, regulating implantation of the egg into the uterine lining  and development of the placenta . While this is not a direct linkage between marijuana and changes in the female reproductive system, it suggests that there may be some effects brought about when ingested.
Marijuana and Male Fertility
The same article mentioned previously also shines some light on how marijuana can affect male fertility. Importantly pointing out two studies with opposing conclusions. One study shows ingesting marijuana (at least at some point) with higher sperm counts and the other correlating marijuana use with lower sperm concentrations.
Currently, research tends to lean towards marijuana having a slightly adverse effect on male fertility, and its consumption leading to lower count and concentrations . Some other studies also point out adverse changes in sperm production and function .
Interestingly, males have their own version of the HPO axis, called the hypothalamus-pituitary-gonadal axis, due to a lack of ovaries. Like in females, the endocannabinoid system also has an important role in this context as well. Some research suggests that males are even more sensitive to changes in endocannabinoid levels than females . Sperm themselves even have both CB1 and CB2 receptors present, indicating a role of the endocannabinoid system in sperm function .
The effects of marijuana on the HPG axis are wide reaching though research is still somewhat contradictory . High levels of marijuana seem to lower testosterone and raise estrogen levels. Animal studies also show some detrimental effects, including reducing testicular size and activity . It is important to note, though, that these findings have been replicated in humans.
Overall, marijuana very likely does have at least some effect on fertility in both males and females. Whether this is as striking as affecting menstrual cycles and changing how sperm cells functions is still up for debate. Of course, if you are considering getting a medical marijuana recommendation, always talk to your physician regarding any questions and concerns you may have.