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THCM: And What It Means for Pregnant Women

THCM from cannabis smoke, and pregnant women
Written by Sarah Friedman

THCM is a byproduct of cannabis smoke that is used to test pregnant women for cannabis use

It’s not good to smoke when pregnant, but that’s obvious because it’s not good to smoke in general. Recently pregnant women have been checked for the compound THCM, to see if they’ve smoked weed while pregnant. What are the implications of the test, and does this make sense?

What is THCM?

First it was THC, and that’s all we talked about with weed. Several years ago CBD became a big name what with the 2018 US Farm Bill. In the last few years, its been all about other minor compounds found in the plant, like delta-8 THC, HHC, THCO, and synthetics like delta-10. There are so many letter combinations, its hard to follow, and even now we don’t really know a lot about these compounds. What we do know, is that they either occur in nature, or were made in a lab.

THCM doesn’t fit into either of those categories. Officially called 11-Nor-Delta-9-Tetrahydrocannabinol-9-Carboxylic Acid {Carboxy-THC}, it was discovered in 1997 (or 1977 depending on your source, for which there aren’t many good ones), and has never been isolated from the cannabis plant, so its effects – and most other information – are unknown. It’s not actually found in the plant, but it is used for a specific purpose.

So far, THCM has only been found, not in cannabis, but as a byproduct of cannabis smoke. To be clear, its not a byproduct of using cannabis in general, but a byproduct that comes from lighting the weed on fire and breathing it in. So if you’re tested for it, and you use cannabis edibles, or vapes, a test for THCM won’t turn up anything. The testing for it is highly specific, and only applies to pregnant women right now.

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How is a person tested for cannabis?

A regular weed test is generally done using urine. And the results depend greatly on the amount a person uses. It picks up THC that entered the system in any way (edibles, vaping, smoking, etc…) For an occasional smoker, it might only show up in the urine for a few days, but this varies by person. Things like body fat content, exercise regimen, and diet can play a big role in how long THC stays with us. For a heavy user, it can take as long as 30 days after the final smoke. For moderate smokers, its likely to be in the middle – maybe 10-15 days.

Then there are blood tests for THC, but we don’t hear about them often. They’re used when the circumstance of testing involves some kind of criminal activity. For example, this testing method is employed more and more on roadways, if a state designates a blood THC level for driving. These tests are way more accurate, but can only tell if weed was used within the last two days. So they don’t cover as much time, and are best for circumstances that involve very recent use.

There are also hair tests, but they’re not very reliable. THC in hair can be detected for months after use, but these tests aren’t terribly specific to use. How many times have you sat in a room filled with weed smoke? You know what else was with you? Your hair. Testing hair doesn’t necessarily mean that a person smoked, it just means they were around smoke. Realistically, you likely won’t ever be given a hair test because of the lack of accuracy.

Why is THCM tested for?

All the above tests are essentially looking for THC, as that’s the psychoactive part of the plant. And while urine tests can usually pick up that a heavy smoker smoked within the past month, and a blood test can tell the same for the past couple days, there is one other way to test for longer periods. Whether it’s actually useful or not is hard to say, but its certainly happening, so I’ll share it with you.

As mentioned, THCM is a byproduct of cannabis smoke. Not of other forms of weed use. It acts as a biomarker, which is “A biological molecule found in blood, other body fluids, or tissues that is a sign of a normal or abnormal process, or of a condition or disease. A biomarker may be used to see how well the body responds to a treatment for a disease or condition. Also called molecular marker and signature molecule.” In this case, it marks whether a person smoked cannabis within the five months before birth.

Yup, it’s used on pregnant ladies to determine if they smoked weed. So let me repeat again, its not whether a person ‘used’ weed in the five months prior to birth, it’s whether a woman ‘smoked’ weed in that time. So, its not testing for weed use technically, its testing only for if a woman smoked it. While it can detect if a fetus was exposed to cannabis smoke in-utero, it doesn’t apply to other forms of weed intake within that same time period; that will only show in urine or blood.

The dangers of smoking while pregnant

We already know smoking is bad. In general, and during a pregnancy. Let’s remember, smoking is the #1 death toll drug; even if its not about a specific compound, but a means of intake. And that’s what it is about. It doesn’t matter if its weed, cigarettes, or some herb given to you by a shaman; if its lit on fire and breathed in, its smoking. And that’s the issue. Tobacco, for example, has plenty of medicinal uses, and its simply the lighting it on fire and breathing it in that’s bad.

As far as what it can do during pregnancy? This isn’t like weed where there are questionable studies making questionable connections. We have years of data on this. Cannabis is not related to the health issues of smoking; so it makes sense to question whether its the cause of issues in-utero, especially when smoking is included. Smoking is not just about cigarettes. (And as a side note, its horrifying I have to keep pointing this out; and that its repeatedly confused in the minds of the public what the actual risks of smoking are, and where they come from.)

Study after study has turned up the results that this review did: Health outcomes of smoking during pregnancy and the postpartum period: an umbrella review. Main results of the 64 studies it analyzed when looking at smoking during pregnancy (SDP) and 46 different health issues?

“The highest increase in risks was found for sudden infant death syndrome, asthma, stillbirth, low birth weight and obesity amongst infants. The impact of SDP was associated with the number of cigarettes consumed. According to the causal link analysis, five mother-related and ten infant-related conditions had a causal link with SDP. In addition, some studies reported protective impacts of SDP on pre-eclampsia, hyperemesis gravidarum and skin defects on infants. The review identified important gaps in the literature regarding the dose-response association, exposure window, postnatal smoking.”

Even this insinuates that how much is smoked and when its smoked is important, and still unaccounted for in much of the research out there. All included studies were done prior to 2017, but I don’t see that as making much difference at this point. What it does show is the continued and measurable aspect of the negative effects of smoking on a fetus.

Dangers of smoking vs vaping while pregnant

So much research comes up on the topic that its hard to deny. Take this paper that was published in The Obstetrician & Gynecologist in 2019 called Smoking in pregnancy: pathophysiology of harm and current evidence for monitoring and cessation. It also reviews tons of literature to come up with many of the same issues. Its first key point is that “Smoking in pregnancy is a risk factor for miscarriage, stillbirth, placental abruption, preterm birth, low birthweight and neonatal morbidity and mortality.”

Dangers of smoking while pregnant
Dangers of smoking while pregnant

Having said that, even this study shows gaps in understanding. While it mentions in one place that “The adverse effects of cigarette smoke are primarily driven by carbon monoxide, tar and nicotine,” it goes on to stipulate later that “Electronic cigarettes are more popular among smokers, but evidence of their safety and effectiveness in pregnancy are lacking.” This actually indicates that nicotine isn’t where the risk is. If it were, electronic cigarettes would automatically come up as causing the same damage, and as of yet, they have not. Contradictions like this should always be noticed in a study, as they can be factors of personal bias, or a researcher’s own misunderstanding of the research they review.

Vaping has shown specifically not to cause the same issues like cancer, heart disease, and pulmonary disease in the general population. And definitive links to the same birth issues are not found with vaping, whereas you literally can’t get away from them when looking at smoking studies. Which indicates again, this isn’t about tobacco or nicotine, no matter how many times the line is said. This doesn’t mean that inundating a fetus with nicotine is okay either, but the bigger health implication, is simply in the act of smoking something.

Do THCM tests matter then?

The reality is that the jury is out on why picking up THCM matters. Cannabis itself is not definitively associated with birth issues, so it’s a bit odd. Studies blaring titles like Birth Outcomes of Neonates Exposed to Marijuana in Utero, go on to stipulate “However, at this time, there are no data to differentiate smoking itself (ie, inhalation of marijuana smoke) vs ingestion of the cannabinoids as the main factor associated with an increase in adverse events, to our knowledge.” As in, this whole study was done, without considering how the cannabis was used. And that if it was smoked, these results are more likely related to the actual smoking, than the weed.

In fact, that study is scarily similar to this study which attempted to link using cannabis to a raised rate of heart attack (myocardial infarction). The big, glaring issue? It only looked at people who smoked it; as in, no other cannabis use was a part of the study at all. And at not one point did the investigators speak about the general dangers of smoking. Its an entire study that backs up that smoking can lead to increased risk of heart attack, but not cannabis.

I have yet to see a real connection made anywhere beyond these smear campaign articles (what else can you call that?) The pregnancy study is no different. As the main method of cannabis consumption in the world is still smoking, that study likely acted as a study on the effects of smoking to a fetus in-utero, not on the effects of cannabis use to a fetus in-utero.

Since there isn’t great research on the actual topic of the direct effect of weed compounds on a fetus when the co-morbid factor of smoking is eliminated; there’s no real reason for the test in my mind. Co-morbid means the existence of two different factors. In research this can cause problems because if one specific thing is being studied (cannabis use on a fetus), and a co-morbid factor exits (smoking), if the co-morbid factor isn’t controlled for, the results are useless. With a lack of info on weed effects to babies in-utero, a THCM test has no value beyond the idea of smoking in general.

Pregnant woman
Pregnant woman


Truth is, a THCM test like this can cause problems for an expecting mother, which are unnecessary. After all, pregnancy is stressful enough, and as cigarette smoking (the real danger) isn’t illegal while pregnant, there’s no reason to test a woman for this. Especially when it might indicate nothing more than a single joint hit from a months before; and that it hasn’t been ruled out that simply having been in a smokey room, won’t bring on a positive result.

*As a note, I am not encouraging any pregnant woman to use any substance. I am merely questioning the usefulness of this specific test.

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About the author

Sarah Friedman

I look stuff up and and write stuff down, in order to make sense of the world around. And I travel a lot too.