Cannabis and pregnancy is a topic of hot debate. On one hand, women have been using cannabis for various purposes during pregnancy for centuries. On the other, the cannabis that we have now is far different from what our ancestors were using. Coupled with legal barriers to scientific study, the overall effects of cannabis on a fetus are shrouded in mystery. Here’s why a group of medical students are demanding more studies on cannabis and pregnancy.
A lack of research
When it comes to research on cannabis and pregnancy, we have a lot to discover. Much of the research on prenatal cannabis use in humans is lacking.
Because of legal restrictions and ethical concerns over testing cannabis on pregnant women, much of the human research thus far is observational, based on self-reporting, and intermixed with other confounding factors like tobacco and alcohol.
Unfortunately, strict research barriers block much of the access to THC for study in laboratory models. So, much of the research that looks into the cellular mechanisms of action of the psychoactive are restricted to animals.
While other mammals also have an endocannabinoid system, there are a variety of ways that cannabinoids work differently in animals like rats and monkeys than they do in humans. This makes piecing together a complete picture of how cannabis affects a fetus very difficult.
Yet, a group of Georgetown medical students decided to try.
Medical students dive into molecules
A group of four medical students from Georgetown University dove into the available research on prenatal cannabis use. They hoped to develop an understanding of the molecular mechanisms by which THC interferes with fetal growth and development.
The team looked at all research from 1975 to 2015 and their study was published in BioMed Central Pharmacology and Toxicology. Some of the primary concerns include:
- Struggles with fertility (miscarriages, inability for an embryo to implant)
- Changes in the fetal brain during crucial moments of development
- Interference with the use of folic acid (key to fetal development and growth)
- Birth defects
- Prolonged exposure to THC because the compound takes a long time to clear the maternal body
- Changes in stem cells
- Changes in blood vessel growth
- Changes in gene expression that lead to cognitive defects
A fetus is like cancer…?
The study’s senior investigator, G. Ian Gallicano, Ph.D., associate professor of biochemistry and molecular and cellular biology at Georgetown, suggests that THC’s tumor-killing properties may also make the chemical harmful to a fetus. He explains,
We also know that THC is a promising agent for treating cancer, because it negatively affects tumor growth and can cause the death of cancer cells. Embryo development has similarities to tumor formation – it turns on growth pathways that are necessary for development. The fact that THC seems to stop cancer growth suggests how damaging the chemical could be for a fetus.
The majority of the information presented in this study came from animal and cell line studies. Many of the studies also looked at either THC or nonpsychoactive CBD in isolation. The fact that we have few studies that look at cannabis in humans, and test the herb in the way it is actually used by humans make the overall effects difficult to gauge.
A meta-analysis of observational studies in humans published earlier this year  found no correlation between prenatal cannabis use and decreased growth, premature birth, or birth defects. These discoveries were made after controlling for tobacco use and other confounding factors.
Older human research from back in the 1980s followed over 20 cannabis-exposed children from birth to 5-years-old. That study found no difference between cannabis-exposed children and non-exposed controls. The children were evaluated for cognitive and behavioral performance as well as overall health status after birth.
These studies were not included in the Georgetown analysis as they did not examine the molecular interaction between cannabis compounds and embryonic or placental cells. So, there seems to be a bit of a disconnect between the cellular research done in animals or outside of the body and the observational studies on cannabis-using mothers.
All in all, the Georgetown students are correct. There is a strong need for more rigorous research on how cannabis interacts with a developing fetus.
However, we need large-scale, longitudinal observational and epidemiological studies just as much as we need studies on molecular mechanisms of action. The body is a complicated network of cells, chemicals, external inputs, and symbiotic microorganisms.
Looking at just one thing in isolation without long-term observational and epidemiological evidence does anything but paint a clear picture of what’s going on in a developing human being.