Marijuana and the Menstrual Cycle: What the Research Says (Episode 552)

Full Transcript: Episode 552

Lisa Hendrickson-Jack:

This is the Fertility Friday Podcast, episode number 552.

Today I’m sharing a brand new episode in my FAMM Research Series, and I thought today’s episode would be a great follow-up to last week’s episode where we were focusing primarily on the impact of marijuana on sperm quality and fertility. So in today’s episode, we’re looking at a study that examined the impact of marijuana on the menstrual cycle — the follicular phase length in particular. And so we’ll be delving into what the research has to say about how marijuana affects the menstrual cycle and fertility as well.

The name of the study in question is “Lifestyle and Reproductive Factors Associated with Follicular Phase Length.” And as the title indicates, it’s not only looking at marijuana, but it’s also looking at a few other different lifestyle factors, including birth control pill use. And so there’s some interesting parallels there.

Now, one of the interesting aspects about the study is that they are looking at the follicular phase in particular. And if you’re kind of curious as to why they would single that part of the menstrual cycle out — so for anyone who isn’t familiar, we could take the menstrual cycle and divide it in half and look specifically at the pre-ovulatory phase, so what is happening leading up to ovulation, and the post-ovulatory phase, what is happening after ovulation takes place. Now that pre-ovulatory phase can also be referred to as the follicular phase, because ultimately it is characterized by that follicular growth and development. In the pre-ovulatory phase of the cycle, our eggs are developing and preparing for ovulation. And so that’s why we also refer to it as the follicular phase. And the second half of the cycle can also be referred to as the luteal phase. And that’s because after we ovulate and the egg is released from the follicle, it changes and turns into what’s called the corpus luteum, which then starts to produce progesterone. And we see the effects of progesterone in our cycle in the second half.

And one of the reasons why the researchers would be focusing on the follicular phase in particular is because it’s actually the follicular phase that’s most sensitive to insults, whether that be stress or nutritional changes or a variety of lifestyle factors. When we’re looking at cycle irregularities — women who have cycles that tend to be longer or shorter, or they’re fluctuating more than eight days at a time — it’s really most predominantly changes in the length of that follicular phase. So essentially, if ovulation is delayed, or delayed by how much, that is causing the majority of those fluctuations of the menstrual cycle. And one of the reasons for that is that although there can be some fluctuation in the luteal phase of the cycle, it does tend to be more limited. So the corpus luteum has a very specific life cycle. And the average luteal phase typically falls somewhere between 11 to 17 days. So there’s less room for change.

So although there can be some fluctuation of a couple of days, unlike the follicular phase — because the follicular phase, a woman could have a 28-day cycle, a 21-day cycle, a 45-day cycle, a 90-day cycle, a 150-day cycle. So there’s certainly a great deal more variation possible in the follicular phase. So I think that’s one of the reasons that the researchers decided to focus on it.

And one of the things that they were saying when they were kind of setting up the study is that they wanted to identify some of the factors that do affect menstrual cycle length, hoping that it can provide some insight into even how these functions work in the body. There was a comment that the researchers made that I thought was really interesting. They said the timing of ovulation can be extremely variable — which is true — so as we talked about, the follicular phase is so variable because ovulation can be delayed due to these lifestyle factors and other factors. So they said the timing of ovulation can be extremely variable both within and between women, and the sources of this variance are essentially unknown. I thought that that was a really interesting comment — that they’re saying we have no idea why ovulation would be varying.

Because when you’re diving into the weeds through cycle charting as your main tool and you’re able to track what’s happening in the cycle, if you track your cycles, you know that you can also note down things that are happening in your life. You can note down your exercise routine, sleep habits, stress — you could write down how well you’re sleeping. I have clients that have tracked almost anything you can think of. They may look at certain symptoms, digestive complaints. And it’s not to say that every possible complaint or every possible thing is going to have a direct impact on your cycle or be directly related to your cycle, but when you start to look at your health situation, symptoms, different things in the context of your menstrual cycle, then these shifts and changes in ovulation become less unknown and less impossible to know — and more, you kind of have a much better sense of, like, oh well, I didn’t really look at it that closely, but that cycle that my ovulation was delayed for seven days and my period came essentially a week later than it usually comes — I also happen to be moving across the country, or I also happen to be traveling, or I also happen to be in my sister’s wedding or whatever. And all of a sudden, now you kind of have a better understanding of how your body and your hormonal cycle and your ovulatory cycle may be impacted by a variety of different factors.

So that’s just some background information, and I wanted to make a comment because I was looking through the study and I thought that’s an interesting thing to say — what do you mean, essentially unknown? Like, we have no idea. Because when you’re tracking the cycle, of course you can — it doesn’t mean you can know definitively in every situation, but the more that you do and you see, the more that you track and you kind of observe your different patterns, you can be more and more certain that this event is not just a coincidence, that it coincided with your ovulation being changed or different than it normally is.

Okay, so they’re laying the groundwork. They’re talking about how the variability in length of the follicular phase is the major contributor to menstrual cycle variability — which is another fancier way of saying what I said at the outset. So they’re really zoning in on this particular part of the menstrual cycle to see if it’s going to fluctuate.

So in order to study this question, the researchers gathered 221 women who they say were trying to become pregnant. And when they enrolled, they discontinued using hormonal birth control in order to conceive. So in this study, they did have women who had recently discontinued birth control, and so certainly as you can imagine, that played a role in the variability of the follicular phase.

In order to identify when ovulation was taking place in the study, they actually had these women provide urine samples so that they could detect the presence of estrogen metabolites and progesterone metabolites. And that was one of the ways that they determined when ovulation was happening and they were able to use that data to assess how long the follicular phase is.

They looked at a variety of other factors as well. They were looking at the women’s alcohol consumption and caffeine consumption, so they did find a way to track and monitor some of the other factors that may have had an impact. And so in order to assess marijuana use and how frequently this was done, by a questionnaire asking the women how many times they smoked marijuana in the past three months. And so they identified different categories — low frequency users versus high frequency users, depending on how much they typically smoked.

They also divided the follicular phase into three groups. Short follicular phases were defined as less than or equal to 11 days. Average follicular phase lengths were considered to be between 12 and 18 days. And a long follicular phase was considered to be 18 days or more.

So what’s interesting about these research studies that look at menstrual cycle length, or a variety of different factors related to the menstrual cycle in particular, is that pretty consistently, no matter what study that you look at, the average follicular phase length or the average date of ovulation, it’s typically somewhere around that 15-day mark. And this study was no different. They found that the average follicular phase length was about 15.5 days. And the range for this average was anywhere from 12 to 19. The women in the study ranged in age from age 21 to age 42, with an average age of about 29 years.

Now, unsurprisingly, the women who had recently come off of oral contraception did have a longer follicular phase compared to those that hadn’t — so on average about 2.3 days longer, which is interesting. It’s not surprising because when we look at the studies of menstrual cycle characteristics when women are immediately discontinuing contraceptives, we do find that some of the most common things that we see in women during that post-pill transition phase would be a longer — that can be in the first few cycles where it’s taking a bit of time for them to have their first ovulation. But typically those first several cycles are a little bit on the longer end in terms of the overall length, and that means that essentially it’s taking longer for these women to actually reach ovulation. So the follicular phase length is longer. It’s also common to see a shorter luteal phase during that time as the body starts to restore its natural hormone cycling situation. So that wasn’t much of a surprise.

But when we actually look at the impact of marijuana use on the follicular phase, I think that that’s where things get interesting, because marijuana use was also associated with a longer follicular phase length after they had adjusted the data and the results for the impact of oral contraception. So compared with the women who did not use marijuana, marijuana users that were occasional users — their follicular phase was longer by about three and a half days on average. And then the more frequent users — their follicular phase was just under about two days longer on average. So they only found these two factors to be associated with a longer follicular phase, which indicates that it is possible, theoretically, that marijuana use is somehow disrupting normal menstrual cycle function — certainly potentially disrupting hormonal balances — because the length of that follicular phase is directly related to what’s happening hormonally.

For example, if your follicular phase is 15 days versus 25 days, that’s 10 additional days of estrogen exposure, because it’s during that follicular phase that those follicles are developing. And as those follicles are developing, they’re making estrogen. So if the use of marijuana is somehow delaying or disrupting normal follicular development, then theoretically it is possible that it is also having a disruptive impact on hormones.

And so what’s interesting about this study is that according to this research, at least, they did find that there was an impact. Marijuana did have an impact on the menstrual cycle. It was pretty consistent. And at least in this case, it was specific to the follicular phase in particular. They didn’t find any evidence to suggest, at least among their study participants, that it had any impact on the luteal phase, or the second half of the cycle. But they did see this marijuana association with delaying ovulation. They also found some evidence of disrupted hormonal balance. They found that the marijuana users had lower prolactin levels and a slightly lower level of peak luteinizing hormone — peak LH levels. They also found that the users had a slower post-ovulatory rise in estrogen and progesterone.

So the researchers did find that there was some level of disruption in specific relation to prolactin levels, LH levels. And LH — luteinizing hormone — has a lot of different functions, but it’s best known for its function in ovulation. And so what happens is about 24 to 36 hours prior to ovulation, we would typically experience what we call an LH surge. And that is actually what triggers ovulation to happen.

So if in this situation maybe the peak LH level was a little bit lower — I mean, at this point we’re kind of extrapolating here — but there is enough information to say, well hey, maybe it’s disrupting, it’s having an effect of delaying ovulation, and maybe it’s causing it to have a slower rise. So it certainly would be a great topic for further research to clarify what exactly is it doing to the cycle, how is it having this impact of delaying ovulation on average, overall, in these women in the study. And then if it’s having an effect post-ovulatory, slowing the rise of estrogen and progesterone — again, what is it doing? Is it having some sort of impact? Is it inhibiting hormone production? Is it lowering it? How is it interfering with it? So these are questions that would be really, really interesting to look at in further research studies.

So another interesting finding is that when they isolated chronic marijuana users, they found a slightly higher proportion of anovulatory cycles compared to the women who did not use marijuana. And so they didn’t necessarily say that this was a significant finding because it’s not like there’s so many cases of anovulation. So they did note that it’s not really that big of a deal because it’s pretty rare to have an anovulatory cycle, so it probably doesn’t mean anything. But they still noted it and they said they found an excess of anovulatory cycles among marijuana smokers. Three of the seven confirmed anovulatory cycles were in marijuana smokers. So 43% of those who had anovulatory cycles were also marijuana smokers, compared to 15% of the marijuana smokers in the study population. So what that means is that marijuana smokers were much more heavily represented in the anovulatory group. So they had a much higher chance of anovulation if that was something that was going to occur.

So although this point doesn’t necessarily reflect what the researchers found in the study, they did mention an animal study that was done in rhesus monkeys to identify if there was an impact of marijuana on ovulation specifically. I mean, in the study they did it very, very differently — I don’t think you can get monkeys to smoke pot. So they had these monkeys, they gave them daily injections of THC, the active component of marijuana, and they did that throughout the cycle. So they gave these injections daily. And interestingly, what happened in the study is that the follicular phase was delayed in these monkeys, or the intervention entirely prevented ovulation. So in that particular study with these monkeys — obviously they are not human beings, so we can’t necessarily directly apply it to what’s happening with us — but in that particular study they did see a very distinct effect, a distinct inhibitory effect on ovulation, where it was either delaying or stopping ovulation from happening. And they mentioned a longer-term study that was also done along these lines, and they found that over time the impact of the THC declined. So initially it would have these kind of strong inhibitory effects, but over time the effects would lessen — so maybe indicating that the monkeys were building up a tolerance to the THC.

So there are obvious differences in these studies that limit our capacity to just blanket say that they’re related to what’s going to happen in a human woman. Obviously in this case they’re injecting the monkeys with it, so that’s going to have a different effect than potentially the inhalation that is typically how women are using it — versus maybe even ingesting, like in the case of gummies, although this study was primarily looking at the smoking of marijuana. So there’s a lot of differences, but again, they pointed it out because there is some evidence to suggest that there could be this negative effect on ovulation, there could be this negative effect on fertility, especially if it’s delaying or preventing it.

And so that’s kind of what is warranting the study here — they’re kind of looking at some of these effects that they’ve seen in animal studies and saying, well, what is the effect in human women?

So what do we do with this information? Where do we go from here? I think that it’s always interesting — obviously I’m super keen to look at what the research has to say. I love delving into studies to see what people are studying and what they’re finding, and I think that it helps us to gain a better understanding of the world.

What’s interesting about this topic is that again, the research on male sperm quality is a lot more definitive because when you can just provide a sperm sample and look at the motility, morphology, look at the count — it’s math. You have a lot more specific data, and you can be a lot more, just if you’re checking boxes or if you’re a very right-brained individual, it gives you more specific data. Whereas with egg quality, although we do have markers of ovarian reserve, it’s not the same in that we can’t have a specific count and we can’t just pull out a woman’s eggs and examine them every couple of months with a test.

So in this instance, when we look at what the research is showing about the impact of marijuana on fertility, there is a more well-established effect of marijuana use related to male fertility than for female fertility — just because of the differences in how we would be looking at the quality. So within the realm of marijuana, though, there’s a lot more research on the female side, specifically on pregnancy-related outcomes. For example, women who smoke marijuana have been found to have lower pregnancy rates, lower infant birth rates, and an increased risk of pregnancy loss. So we do have data on the impact of marijuana potentially on fertility, on pregnancy, and birth outcomes. And then there’s limited studies looking specifically at the impact on the menstrual cycle specifically. So I think that’s where this information is interesting, because it is providing some additional data on how marijuana could potentially affect the cycle itself.

And anything that has an effect on ovulation — whether it’s delaying ovulation, lengthening the cycle, if it’s having a negative impact on the hormones — then it is telling us that it’s doing something, it’s disrupting. Because not all factors have that significant of an impact on the follicular phase in general. And interestingly, in this study, it seemed as though the marijuana smoking had a higher impact than the contraception, and that’s very interesting in and of itself — that it would have such a significant impact on the follicular phase length.

So a couple things to consider with the study. They said at the outset that they were looking at women specifically who were trying to get pregnant and just kind of monitoring their use and their self-reported use of marijuana and things like that. And so one of the things that the researchers mentioned was that there’s a fairly limited number of women who would potentially be actively trying to conceive who are currently moderate to heavy marijuana users, because many women who are trying to conceive are going to modify their behavior to optimize their chances. So there’s not necessarily this large group of women actively trying to get pregnant who are also using marijuana — is what they were saying. And so certainly what this means is that there’s more room for research in this area, and I suppose from a research standpoint it may be a challenge.

Maybe one of the reasons they chose this specific population of women who were specifically trying to conceive is because these are women who wouldn’t be on contraceptives, where they could actually access the menstrual cycle in its natural form and see what the impact is. Whereas in the general population, I don’t know how easy it is to find 200 women who are not actively taking contraceptives in one shot. So that could be one of the reasons that they chose this population, and that could be one of the challenges to actually ascertaining this information — to actually find women who are not on hormonal birth control, who are cycling naturally, who are using marijuana, where they can actually check to see how it’s impacting or at least comparing the marijuana users to the non-marijuana users, but not having the confounding issue of hormonal contraceptives — because of course, if someone’s on hormonal contraceptives, they’re in most cases not ovulating regularly, and therefore you wouldn’t be able to assess the direct impact of marijuana on the actual cycle length or any of these other cycle factors.

So I think the bottom line in the study — although I feel like the sperm studies are a little bit more satisfying, a little bit more definitive — it does tell us that it’s having an impact. So if you are looking to try to conceive, I don’t think this is surprising. I don’t think anyone thinks marijuana is like a health food or that it’s going to boost your hormones or anything like that. I don’t think we’re under any assumption that marijuana is actually really good for us or anything. But it is useful to see what the research has to say about it. And so I think what we can draw from the study is that there is a potential that marijuana could disrupt ovulation to some degree, it can delay it, and it has the potential to disrupt the natural hormone balance.

Now, to what extent may depend on the quantity of marijuana, because again, it really depended on the amount of use — where the moderate users seem to have the greatest impact. One thing about the study that I thought was interesting — so if I compare how they went about it in this study versus the previous one that we talked about last week related to the men — in last week’s study they were more specific about the use and they had a lot more clearly defined categories. Their questionnaire was more detailed, so you got a better sense of how frequently the users were using it and just a better sense of how much they were using. Whereas in this particular study, based on what they shared about how they asked about it, it was more like how frequently did you do it in the last three months. So I think there is also an opportunity to be more specific so that we could get more data on, like, is it related to how frequently, is it related to how much they’re using? Is a binge user — someone who smokes a whole lot in one day but doesn’t do it every day — do they have the same impact as someone who does a little bit every day? That kind of stuff.

So I think, as with all research, there are still lots of questions that could be useful to have answers to. But with that said, it doesn’t seem like it’s beneficial. So whether you know, binging it a lot versus doing it daily versus once in a while — we can get into the weeds on that — but overall it doesn’t seem like it’s going to have a positive impact on egg quality, which is a surprise to exactly no one.

We should also be concerned about the animal studies. Of course, they can’t be replicated in human beings — like, I just don’t see it being ethical to inject people with straight THC for the purpose of research to see what impact it has on their menstrual cycle. But we should be concerned that when they injected the THC into the monkeys, some of them stopped ovulating. I think we should be concerned about that. And I think again, we can’t draw specific conclusions from that, but looking at that, we can ask a lot of questions and say, maybe it’s not good for fertility and for ovulation if that’s the potential.

And then the fact that they built up a tolerance and eventually it didn’t have as strong of an effect — I mean, that’s also interesting. But again, not a health food.

So I hope that you found today’s episode interesting. I hope that you found it to be a useful follow-up to our discussion of marijuana use in men. I always find it interesting to jump into these topics to see what the research has to say and see what we can gather from it. So I hope that you’re having fun nerding out on these topics as much as I am. And so with that said, I hope you have a wonderful weekend — whenever you’re tuning into the show. If you can think of someone who would benefit from hearing this, if you have a friend or a colleague or a client who you think would really enjoy a deep dive into this type of a study, then feel free to share. The share link is fertilityfriday.com/552. And so of course, I hope you enjoy the rest of your day, and as always, until next time — be well and happy charting.