The effect that weed has on the body’s immune system is a highly contested subject, full of contradictions and misleading studies. A 1992 review paper in the Journal of Psychoactive Drugs went so far as to say that “Few areas of scientific research have been as controversial as the effect of marijuana on immune defenses.” The study into this field began mostly in the 1970s and then was invigorated with studies on the effects of cannabis regarding AIDs patients in the 1980s. However, even by 2017, there seems to be no consensus on the issue. In this article, we will try to elucidate out some of the facts concerning how smoking weed will affect you when you have a cold, and separate them from the myths. 

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What Causes A Cold?

The common cold is not just one disease, it is actually a general term for the condition caused by over 200 different types of viruses, most often Rhinoviruses and Adenoviruses. When we are exposed to this virus through various transmission vectors, then our body is either able to fight it off or we become sick. Symptoms include inflammation of the throat and lungs, excess mucus production, runny nose, sneezing, and headaches.

The factors determining how well equipped our body is to fight off such viral infections are broad and difficult to quantify but include things like sleep, exercise, diet, stress, and other internal and external factors that affect our immune health. There is plenty of evidence to show that cannabis acts as a pain reliever, anti-inflammatory, and sleep aid; all of which are intuitively good when considering cold symptoms. However, some studies have implied that cannabis consumption reduces immune responses, thus increases chances for infections.

woman drinking hot tea and feeling comfortable iStock / tommaso79

The Endocannabinoid System and Immunity

Over the last two decades, the science behind the body’s endocannabinoid system has been progressing rapidly. We know understand that this system plays a vital role in the regulation of multiple systems of the body, including the immune system. It was also found that nearly all of the various types of immune cells contain receptors for the bodies endocannabinoids, and thus science is able to describe a mechanism for the action which exogenous cannabinoids such as the THC, CBD, and others from cannabis play.

According to a 2014 review, the current understanding is not that these cannabinoids necessarily support or suppress the immune system, but act in concert to maintain homeostasis within the body, making sure the immune system is never too weak nor too strong. There are many parts of the immune system, including macrophages and white blood cells.

Macrophages certainly can play a role in viral defense, however, the cell most directly responsible for killing cells infected with viruses is the cytotoxic T cell. This type of cell detects when normal cells are infected by viruses and then releases cytotoxins to kill that cell. Small molecules called antibodies and interferons also play an important role. Macrophages come into play as they have a role in activating T and B cells and they engulf and kill viruses and bacteria that are marked with antibodies.

Weed and Immunity to Colds

Throughout the 1970s there were several studies and reviews published claiming negative effects of cannabis on immune health. However, most of these studies are contested based on multiple grounds, including researcher bias, conclusions made from animal studies, and studies that used extremely high doses of THC. In a 1992 review, it was concluded that of all the studies performed thus far, in no way did any of them show evidence of immunosuppression, and there was great inconsistency between studies and an inability to replicate them. Even though some studies did show negative effects, these were largely on rats or in petri dishes.

Some studies looked more closely at how each particular immune cell responded THC and CBD. Several dozen studies were reviewed in the Journal of Immunology in 1998 which found that various cells either increased or decreased with exposure to cannabis. In the studies, T Cells either decreased or stayed the same, B cells either increased or decreased, and both macrophages and Natural Killer cells neither increased or decreased. This variability gives further evidence for the immunoregulatory effects of cannabinoids, rather than a conclusion of immune support or suppression.

However, it should be noted that although many studies did find changes in the abundance or proportion of various immune cells, no study ever found that those effects directly affected human immunology nor did any study determine that cannabis users had a higher risk of infections, although THC was found to be immunosuppressive in vitro. A recent review from 2017 concluded that there is just not enough scientific evidence, despite so many studies, to support or deny any of the claims regarding cannabis use and immunity.

OG Kush OG Kush strain (iStock / HighGradeRoots)

So, should I smoke weed when I have a cold?

Cannabis has been shown to positively affect some of the symptoms of a cold, reducing inflammation, relieving pain, and improving sleep. However, don’t grab that joint just yet. Although the cannabinoids and terpenes in weed may help you feel better, smoking most likely will not. Several studies have shown that smoking, whether it be tobacco or non-tobacco products, leads to a higher rate of chronic bronchitis, production of sputum, wheezing, and reduced lung function.

Other studies have also found that smoking itself reduces the abundance of viral fighting macrophages in the lungs and thus increases the chances of infection by a variety of airborne pathogens. Lastly, sharing joints or smoking devices can further spread the disease, and should be avoided when you are sick. Even though the science is still ambiguous if you think weed is the answer to help relieve some of your cold symptoms, instead of smoking it you may want to try other routes of consumption. Teas, edibles, and tinctures are most likely your safest bet and can be combined with other helpful herbs such as echinacea, lavender, lemon balm, or ginger.