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Is It Safe to Use Cannabis During Pregnancy?


After widespread legalization across the U.S., medical and recreational cannabis use is becoming more acceptable. Thanks to the untiring efforts of biomedical scientists, the medicinal benefits of cannabis are being proven beyond a reasonable doubt. As medical marijuana use increases, so do the safety concerns for the general population as well as special groups, such as elderly people, children, and pregnant women.

While marijuana use in pregnancy is already a hot topic for scientific debate, a recent study has warned that pregnant women must shun cannabis to avoid complications, particularly for their unborn child. Upon reviewing several published studies, this particular study concluded that maternal cannabis use can increase the risk of anemia in pregnant women by 36%, while the unborn’s in utero cannabis exposure can increase the risk of low birth weight by 77% and related neonatal intensive care unit (NICU) admission two fold. As marijuana is becoming more accessible, understanding both the benefits and side effects, particularly in this special population, stands as our top priority.

Just because something has been published in peer-reviewed scholarly journals doesn’t mean it is scientifically accurate or the final opinion of the scientific community. As an independent scientist, I’m here to critically appraise the scientific strengths, limitations, and possible/potential biases of this review study.

Limitations of the Study

Upon reviewing the study, all I can say is – the study did not come without limitations. Let’s have a look at in detail.

  1. The study exclusively relied on self-reported measures of cannabis use and potentially underestimated the prevalence or history of other drug(s) use of pregnant study subjects. Other drug(s) use may be due to social desirability, drug dependence, and addiction.
  2. As with other similar studies, the present study did not exclude subjects with history of poly-substance use/abuse. Most hard drug abusers, tobacco users and alcoholics are cannabis users but not vice versa. Hence, the exact ‘cannabis-only effect’ on pregnancy has not been determined by researchers. Properly designed, additional studies are required to draw definitive conclusions.
  3. Certain maternal and fetal outcomes were measured using the same cut-off points in most of the reviewed studies. Furthermore, different studies reported varied outcomes that were not reported in other studies. For example, one study has reported incidence of jaundice with low birth weight while two other studies reported incidences of fetal distress with low birth weight and hypoglycemia with low birth weight. With varied outcomes, the study could not draw any definitive conclusions.
  4. The meta-analyses study included 24 studies including case–control studies, cross-sectional, and cohort studies but not a single randomized-controlled study, which is universally considered as a reliable clinical trial study design to reduce/eliminate study bias. This is a notable limitation of the study.
  5. Although, the review and meta-analyses study found prevalence of maternal anemia among cannabis users, the study cannot find any association between the incidence or prevalence of maternal anemia and cannabis use. The study authors warned that the results should be interpreted with caution, and recommended further studies to confirm their findings.
  6. Similarly, the study found an increased rate of neonatal intensive care unit/hospital admissions for cannabis-exposed infants. However, some of the important neonatal outcomes and growth parameters, such as head circumferences, gestational age and length were not significantly demonstrated in the present study. Other observed growth parameters remained notably inconsistent. These drawbacks call for a question about the viability of this study.
  7. The study mostly focused on Apgar score as a neonatal assessment variable among in utero cannabis exposed infants, but the results could not demonstrate significant association. Additionally, the effects of cannabis use on neonatal assessments including, Prechtl and NBAS, were not adequately discussed in the literature.
  8. The inclusion and exclusion criteria were not properly designed. The study did not strictly include the relevant studies with subject’s maternal age of 18 years and older.

To understand and assess the effects of a drug, understanding the fetal and maternal outcomes are essential. Other confounding factors, such as heavy alcoholism and tobacco use, can cause adverse outcomes such as low birth, maternal anemia, anomaly and in utero low weight problems etc. Even the researchers of this study were not sure whether the observed adverse events were related to cannabis use or due to other drugs use (tobacco and alcohol). Meaning, the cause-and-effect of cannabis use and these adverse outcomes could not be established by the study. Hence, additional studies are warranted to eliminate the confounding factors with utilization of appropriate age-matched control groups.

Reported Results are Mixed and Conflicting

Surprisingly, the meta-analyses and review study that I’ve critically appraised is not the only study that reported inconclusive results. Here are the other botched-up studies with either mixed or conflicting results.

In one study, no plausible association was observed between 1 and 5 minute Apgar scores and neonatal behavioral assessment scales among in utero cannabis exposed infants. Similarly, a demographic study conducted in Jamaican and Costa Rican people (recreational cannabis use) have failed to show any negative effects in cannabis-exposed unborn.

Among the five studies that investigated the association between the gestational age and in utero cannabis exposure, four studies observed a null association between these two factors, while one study found a significant decrease in gestational age among in utero cannabis exposed infants. Additionally, further studies on fixed-effects models have failed to demonstrate significant association between gestational age and in utero cannabis exposure.

Other independent studies have found no remarkable association between in utero cannabis exposure and number of hospital stay days, risk of developing jaundice, abnormal fetal resuscitation, occurrence of respiratory distress syndrome and other complications such as perinatal mortality, anomaly, abnormal fetal tests, fetal heart rate of the pulmonary arteries or aorta, aortic peak systolic velocity, sepsis, hypoglycemia, spontaneous abortions, intubation requirement after delivery, abruption and fetal distress.

Despite these conflicting evidences, one study has found a notable increase in mutant lymphocytes in the blood samples of pregnant mother and the unborn. However, another study has found no increased risk of chromosomal abnormalities (spontaneous abortion karyotypes) in pregnant cannabis users.

Taken together, the study has shown some degree of correlation between cannabis use and NICU/ICU admission. With these limitations, the study results do not appear to be conclusive and further assessment of these results in a homogenous population is required.

A scientifically-sound study with conclusive results could benefit pregnant women to help them better understand the pros and cons of cannabis use, and also to make informed decisions.

Looking into the Reality

Forget about the reported side effects of this study, if we look at the other studies and historical evidence, cannabis appears to be useful to treat various gynecological and obstetrical problems. Self-reporting and anecdotal evidence has shown that weed can help pregnant women to treat morning sickness. The American Medical Association has called for warning labels for marijuana (both medical and recreational use) about the possible risk during pregnancy but it has not been imposed. It seems most pregnant women are not concerned by these study results. They tend to use marijuana to relieve morning sickness, labor pain, and also for quicker labor.

As endocannabinoids may influence the modulation of parturition and pregnancy, cannabinoids may mediate a direct role in myometrial contraction via CB1 receptor action. This benefit might be helpful to induce labor, nonetheless only if the potential benefits of cannabinoids outweigh possible adverse events.

If these studies have reported several obstetrical benefits, why are there no mentions about any side effects in the unborn? Are these fears unnecessary?

I want to leave these questions to you, the readers, but would love to hear their thoughts.

Based on my review of this study, I’m not here to say marijuana is completely safe to use during pregnancy.

“Nothing is a medicine, nothing is a poison – the right dose differentiates the poison and medicine.” – Paracelsus (Father of Pharmacology)

As legalization of medical cannabis is underway, it is very difficult to initiate/conduct clinical trials right away, for all ailments. It may take some time. So, it is not possible to determine the effective dosage, side effects and contraindications in patient population, particularly in pregnant women and unborn. Until it happens, we need to be in wait-and-watch mode.

Better safe than sorry!


  1. Thank you for looking so closely at the review study. Although you acknowledge cannabis may have beneficial effects during pregnancy, I predicted while reading this that you would nonetheless advise against using it (as pretty much all male writers do). I certainly agree there needs to be more study on the issue. In the meantime, I have talked with mothers who have decided against using cannabis during pregnancy despite severe morning sickness (which often lasts all day); more than one of them has lost their child due to effects of HG. You err when you say there were no ill effects among Jamaican mothers in a behavioral study; in that March of Dimes sponsored study Melanie Dreher found that babies born to marjuana-using mothers scored BETTER on developmental tests than the babies of nonsmoking mothers, and the children of Roots Daughters who smoked the most ganga did even better. (A second follow up study was not funded.) Also endocannabinoids are found in breast milk and may be important for the suckling response (see: http://wecan702.com/cannabinoids-like-those-found-in-marijuana-occur-naturally-in-human-breast-milk/). A recent study of some 5000 mothers out of Australia showed a correlation between marijuana smoking and a few (11) pre-term births if mothers continued to smoke after 20 weeks; the correlation was not found for mothers who smoked at 15 weeks (see: http://www.sciencedirect.com/science/article/pii/S0890623816300715). This could be good news for mothers since many experience the most severe nausea early in their pregnancies. More studies are reviewed at: http://norml.org/about/item/breathe-push-puff-pot-use-and-pregnancy-a-review-of-the-literature; also see: http://tokinwoman.blogspot.com/2014/11/please-let-princess-kate-smoke-pot.html. I try to analyze and post studies as they come out at: https://www.facebook.com/tokinwomen/

    • Thank you for your interest in this article.

      Yes, I want this special population in a safe harbor position, because it’s good to stand with evidence-based medicine. I can’t wait to see large-scale studies.

      Of course, Hyperemesis gravidarum is dangerous if left untreated. I believe cannabis has the potential to treat HG, Its not about efficacy but safety. At this point, safety studies are badly needed. I think, cannabis might be safer than any other approved drugs and even nutritional supplements. But until see have the proof, it is better to avoid it.