Motion Sickness, Stress, and the Endocannabinoid System

Motion sickness is annoying and messy. For those with motion sickness, traveling becomes a drawn-out torture scenario with every turn of the road or spin of the fair ride or rocking of the boat. Your eyes see one thing, your ears sense another, your muscles feel something else, your brain receives all these mixed signals, and you end up feeling clammy and sick. Many of us have been there. Many of us have tried almost everything to make it stop. A lot of us have also wondered what goes on in our bodies when it happens. That’s what we will dissect here today.

What Causes Motion Sickness?

It has been found that between 7 and 28% of individuals experience motion sickness while traveling by road, air, or sea. The traditional science behind motion sickness points at “neuronal mismatch theory”. When you are in a car, plane, or a boat, your body receives inputs from three sources - inputs from the position and movement of your body, inputs from the inner ear, and visual input. For those with motion sickness, these inputs fail to coincide with those expected on the basis of previous exposure history.

While this theory talks about motion sickness in general, it does not explain individual susceptibility to motion sickness or risk prediction. Recent studies have shown that a large part of individual susceptibility to motion sickness can be attributed to genetic predisposition. While it could be in your genes, the question is, how exactly is nausea triggered? Nausea and vomiting symptoms are linked to the activation of two things in the body:

1. Glucocorticoids, which are steroid hormones produced by the adrenal glands
2. Symphaticoadrenergic stress response systems which is a group of organs and nerves that regulate our cardiovascular functions. This system is responsible for stimulating the body’s fight or flight response.

In addition to the above, the enteric nervous system, also known as the gut-brain interaction kicks into action in stressful situations for those with acute motion sickness. Such gut responders experience nausea and vomiting. Interestingly, what regulates the interaction between the gut and the brain is the endocannabinoid system (ECS).

What is the Endocannabinoid System?

The endocannabinoid system is a network of chemical signals and cannabinoid receptors spread throughout the brain and the body that maintain a state of equilibrium in the physiological functions of the body. It comprises two receptors named CB1 and CB2, cannabinoid molecules that send signals for the receptors to pick up, and some biosynthetic enzymes that create and disintegrate these cannabinoids.

The ECS works like traffic cops across the body that regulate our physiological functions by turning up and down the activity of the system that needs to be adjusted - like appetite, stress, temperature, attentiveness, mood, etc. The ECS has a profound hold on the gastrointestinal functions in the GI tract, also known as the gut. Apart from the ‘gut feeling’, the gut is also famous for its response to stress which is one of the main reasons why you feel nauseous when you are anxious.

The ECS connects the physical and emotional stress responses with the gut functions and energy regulation. This means your ECS tells your body to either react to or not react to the three sensory inputs (discussed above) that trigger motion sickness, in an attempt to restore balance in your body. This is why the ECS is also known as a general stress recovery system.

How is the ECS Connected With Stress & Motion Sickness?

Several studies have been conducted on how the endocannabinoid system reacts to motion sickness triggers and what actually goes on behind the scenes. One study was conducted on 21 volunteers in an aircraft using parabolic flight maneuvers that mimic zero-gravity conditions inside the aircraft. Blood samples were taken inside the aircraft before conducting the maneuvers, in between the maneuvers, after the end of the maneuvers in-flight, and also 24 hours later to study the activity of the ECS. 

Volunteers that developed acute motion sickness had significantly high stress scores, which is quite obvious. Surprisingly, they also exhibited low endocannabinoid levels during the parabolic flight. Specifically, the endocannabinoid, 2-AG dropped during the maneuver and remained unchanged throughout the experiment. On the other hand, participants without motion sickness symptoms had higher levels of endocannabinoids, both 2-AG and anandamide. 

Another noticeable distinction was observed in the gene expression of these two groups of participants. Gene expression is a process by which information in a gene is converted into a functional product, such as a protein, through mRNA molecules. Gene expression is how a cell responds to changes in the external environment. For those with motion sickness exhibiting nausea and vomiting, the mRNA expression in leucocytes (also known as white blood cells, which counteract foreign substances in the body) was found to be significantly lower than those without.

A different observation from the same experiment showed a more detailed and interesting finding. The two endocannabinoids, anandamide and 2-AG play different roles in response to stress and motion sickness. Change in the anandamide level happens early in the parabolic flight maneuver and seems to be associated with nausea and stress reaction. But the 2-AG level increases later and brings in a stress recovery response immediately after the maneuver. 

How CBD Helps

One crucial conclusion can be drawn from the above experiment - a failure to up-regulate and maintain endocannabinoid signaling during the external triggers can result in a high risk of developing motion sickness with the full package of nausea and vomiting as well as a stress response. Now the question is, how to stop motion sickness?

Turns out, there’s a way around this problem. Plant-derived cannabinoid, CBD has been found to optimize the functioning of the endocannabinoid system by protecting the anandamide levels in the blood, which otherwise drops significantly causing nausea and vomiting. CBD does this by inhibiting the enzyme, fatty acid amide hydrolase (FAAH) whose role is to break down the endocannabinoids. This keeps the anandamide level intact, which in turn activates the ECS receptors located in the nausea-triggering region of the brain. A higher level of anandamide keeps motion sickness at bay.

In short, CBD keeps the sympathetic nervous system (remember fight or flight?) from going all crazy as soon as the flight takes off or you hit the gas, thus kicking both stress and nausea to the curb. 

Conclusion

Here’s a quick summary of what we have learned so far. The traditional theory behind what causes motion sickness goes something like this - it is triggered by a disparity between the sensory inputs when we are in motion and past exposure history. Some of it can also be attributed to genetic disposition. However, a more modern theory suggests that the endocannabinoid system has a role to play in motion sickness. Studies have confirmed that endocannabinoid levels drop significantly in subjects that have motion sickness, causing nausea and vomiting. Even though there is no definite answer to how to stop motion sickness, CBD has been found to have some positive effects given its ability to optimize ECS functions. In other words, if you suffer from motion sickness, CBD might just be the solution you were looking for.