Into the Weeds- Marijuana, CBD, and Brain Health

by Kayee Liu MS, RDNLifestyle
Marijuana plant on a desk

How many words do you recognize from this list: marijuana, cannabis, hemp, cannabidiol (CBD), CBD oil, 9-tetrahydrocannabinol (THC), weed, pot, hashish, kief, terpenes, ganja, grass, herb, blunt, joint, reefer, bud, Mary Jane, skunk, boom, blaze. It’s overwhelming- so many words, so many connotations. Since the recent legalization of marijuana, conversation about marijuana has been at an all time high (pun intended). So let’s delve into what this little herb is and how it could affect your health.

Are hemp and marijuana the same?

Before we get into the history, let’s clear up some common misconceptions. Marijuana and hemp are part of the same species but are VERY different plants. Cannabis is a genus of the Cannabaceae family (the order goes Family → Genus → Species). In this genus are three known species, Cannabis Sativa, Cannabis Indica, and Cannabis Ruderalis. Hemp and marijuana are both from the Cannabis Sativa species. However, much like cows from different parts of the world differ from each other, so do these Cannabis plants.

Most of the THC, the psychoactive ingredient that gets people “high”, is found in the leaves of the Cannabis Sativa plant. Hemp plants are tall with thin leaves and longs stems; not surprisingly, they also have high CBD and low THC (<0.03%) content. Marijuana plants are bushier with broader leaves and shorter stems; they have low CBD and high THC. Both varieties will have THC, but the CBD in hemp minimizes the psychoactive aspects of THC. The long stems of the hemp variety are also very fibrous and can be used for industrial/commercial purposes including paper, textiles (fabric), clothing, biodegradable plastics, paint, insulation, food, and animal feed. The broad-leafed, marijuana plant is often packed with THC and used medicinally or recreationally for various reasons.

History of Cannabis

The history of cannabis dates as far back as 10,000 years ago with early recorded use of hemp around Central Asia in the regions of what are now Mongolia and Southern Siberia; cannabis carries the distinction as one of the oldest cultivated crops in recorded human history. Many bold claims have been made about its spread. Ancient legend reported marijuana use began at approximately 2737 B.C. (approximately 5000 years ago) under Emperor Shen Neng in China; marijuana was used medicinally and found to manage gout, rheumatism, malaria and absent mindedness. From approximately 2000-1400 B.C., India found uses for the plant medicinally, recreationally, spiritually, and religiously. The next recorded civilizations using marijuana were the Europeans around 500 A.D. as a form of folk medicine. Marijuana reached Persia and North Africa in the form of hashish (because alcohol was banned religiously) at approximately the 12th century.

Multiple claims exist on its passage to the Americas with no clear consensus, with some saying it reached the New World during the Columbian Exchange while others saying the Spanish brought cannabis with them to South America, all around the 1500s. The English brought the hemp crop to Jamestown in the 1600s along with tobacco and farmed them on plantations. The use of hemp has been pervasive in North American history and was a staple product used for various supplies like rope, paper, and clothing. In 1850, marijuana entered the U.S. Pharmacopeia (the book on every medicinal drug) for its uses in rheumatism, nausea, and labor. The Mexican Revolution in 1910 brought many immigrants along with recreational marijuana use. Anti-racial sentiment throughout the 1910s and 1920s led to a gradual villainization and criminality associated with its use that was often blamed on black and Mexican communities. The term “cannabis” was eventually replaced with “marijuana” to draw attention to its Mexican etymology and associated with a negative connotation. By the 1930s, it became a primary target for the post-Prohibition drug wars led by the early Drug Enforcement Agency. Unlike the Prohibition, federal marijuana laws have consistently stymied their production, sale, and criminalized possession. In 1970 during Nixon’s “War on Drugs”, marijuana was categorized as a Schedule 1 drug along with heroin and LSD with the Controlled Substances Act. Since 1993, marijuana has gained positive traction in public opinion; greater than half the US states, including California (which makes up 12% of the US population), have broadly legalized the substance for medicinal use.


What’s the difference between these two chemicals you might ask? Cannabidiol (CBD) and 9-tetrahydrocannabinol (THC) are both phytochemical compounds called cannabinoids found in Cannabis Sativa. They imitate our bodies natural endocannabinoid system by acting on the receptors that allow cells to communicate and stimulate further reactions in our body. Basically they pretend to be our bodies chemicals and activate receptors that are involved with inflammatory, respiratory, cardiovascular or our immune cells. CBD is non-psychoactive while THC is psychoactive; both have found uses in certain areas of medicine. CBD has been developed into drugs in early 2018 to manage symptoms of epilepsy while THC has been made to produce drugs like Marinol, a medication used for treating nausea and vomiting that is often associated with cancer and chemotherapy. Recent trends have seen CBD being introduced into foods and have been suggested to treat various illnesses including but not limited to: cancer, chemotherapy, glaucoma, post-traumatic stress disorder, cachexia, muscle spasms, epilepsy, severe nausea, eating disorders and pain management. However, the strength of the research on these other suggested effects are generally unclear.

What about the health risks of smoking?

Hopefully you already know that smoking is bad for your health. But is smoking weed any different than cigarettes? Most uses of marijuana are often in the form of smoking so it’s inevitable we think about the health of our lungs. The NIH (National Institutes of Health) reports that, so far, researchers haven’t found higher risks of lung cancer in marijuana smokers. This decision was made based on a consensus report from the National Academies Sciences (The Health Effects of Cannabis and Cannabinoids, 2017) . These statements mainly pull their sources from a study done in 2015 that says after pooled analyses; there was little evidence of increased lung cancer risk in habitual or long-term smokers (Zhang et al., 2015) . Hold on. They continue further saying “although the possibility of potential adverse effect for heavy consumption cannot be excluded”. Other earlier studies have stated heavy cannabis use was associated with 2- fold risk for lung cancer, even after adjusting for tobacco use, age, alcohol consumption, socioeconomic status and respiratory conditions. (Callaghan, Allebeck, & Sidorchuk, 2013) Something of note is that the studies are specific when mentioning heavy use of marijuana as opposed to medium or low use of the drug in their findings. At the end of it all, the research is still conflicting as to its effects but it seems like heavy usage of the drug (and of smoking in general) is likely putting your body at risk.

It should also be noted that maternal exposure to marijuana during pregnancy could lead to dysregulation of the immune system of the developing fetus. This could potentially lead to immune deficiencies, infection, and even cancer later in life (Dong et al., 2018). All drug use should be avoided during pregnancy and lactation for the safety of the fetus.

How does marijuana affect brain health?

So what does marijuana actually do to my brain health? Great question. I’ll start with dopamine; in its most simplistic sense, dopamine is a neurotransmitter that is released in the brain that essentially makes rewards enjoyable. Based on current research, cannabis works by raising dopamine levels in the striatum, the part of your brain that manages reward. Typically, drugs work by either increasing how much dopamine is released or blocking the place where neurotransmitters, like dopamine, go. Marijuana is not associated with lower dopamine uptake, that deadening of the reward system that causes dopamine to float around longer, which is the hallmark of using narcotics (Ghazzaoui & Abi-Dargham, 2014). Though marijuana uses the same neurotransmitter as certain illicit drugs, like amphetamine or meth, it does not work the same way. It is also notable that dopamine spikes are not as strong as those seen in hard drugs like meth (Bossong et al., 2015).

What researchers have also found is that severe cannabis use means a possible deficit in the dopamine releasing mechanism; so, marijuana can be harmful to the brain if you use it too much. The researchers also wanted to make a note that rather than marijuana causing low dopamine release, patients might already have low dopamine, which pushes them to use cannabis in the first place, a chicken and the egg dilemma of which came first (Van de Giessen & Weinstein et al., 2015). Another study noted mild to moderate cannabis use is not associated with striatal dopamine deficit; using less marijuana  doesn’t have this dopamine deficit effect on the brain. However, those who start using at a younger age, or had a longer duration of use, did see lowered dopamine release over time. (Urban et al., 2012)

What’s the takeaway?

Overall, from the studies we’ve seen so far, marijuana doesn’t seem to cause problems when used for a minimal amount of time. Abuse and overuse of the drug has been shown to cause negative effects on brain health, so if you choose to use marijuana, make sure you’ve done your research and have properly weighed the risks and benefits. And of course, find a way to use this plant without smoking it. On a final note, I want to say that quality research (that controls and accounts for other factors) into marijuana has been lacking because of the Schedule 1 title. Now that marijuana is starting to become legalized in the U.S. and fully so with our friendly neighbors North of the border, new research is finally being conducted on the potential efficacy and safety of these substances. If you’re interested, try to keep an eye out in the near future for research about marijuana. Who knows what interesting findings will come from such a young, budding industry.


Bossong, M. G., Mehta, M. A., van Berckel, B. N. M., Howes, O. D., Kahn, R. S., & Stokes, P. R. A. (2015). Further human evidence for striatal dopamine release induced by administration of ∆9-tetrahydrocannabinol (THC): selectivity to limbic striatum. Psychopharmacology, 232(15), 2723–2729.

Callaghan, R. C., Allebeck, P., & Sidorchuk, A. (2013). Marijuana use and risk of lung cancer: a 40-year cohort study. Source: Cancer Causes & Control, 24(10), 1811–1820.

Dong, C., Chen, J., Harrington, A., Vinod, K.Y., Hegde, M.L., & Hegde, V.L. (2018). Cannabinoid exposure during pregnancy and its impact on immune function. Cell Mol Life Sci. DOI:10.1007/s00018-018-2955-0

Elsmarieke van de Giessen, Jodi Weinstein*, Clifford Cassidy, Margaret Haney, Zhengchao Dong, Rassil Ghazzaoui, Najate Ojeil, Lawrence Kegeles, Xiaoyan Xu, Nehal Vadhan, Nora Volkow, Mark Slifstein, A. A.-D. (2015). Deficits in Striatal Dopamine Release in Cannabis Dependence. Neuropsychopharmacology : Official Publication of the American College of Neuropsychopharmacology, 40 Suppl 1(Suppl 1), S106-271.

Ghazzaoui, R., & Abi-Dargham, A. (2014). Imaging dopamine transmission parameters in cannabis dependence.

The Health Effects of Cannabis and Cannabinoids. (2017). Washington, D.C.: National Academies Press.

Urban, N. B. L., Slifstein, M., Thompson, J. L., Xu, X., Girgis, R. R., Raheja, S., … Abi-Dargham, A. (2012). Dopamine Release in Chronic Cannabis Users: A [ 11 C]Raclopride Positron Emission Tomography Study. BPS, 71, 677–683.

Zhang, L. R., Morgenstern, H., Greenland, S., Chang, S.-C., Lazarus, P., Teare, M. D., … Hung, R. J. (2015). Cannabis smoking and lung cancer risk: Pooled analysis in the International Lung Cancer Consortium. International Journal of Cancer, 136(4), 894–903.