Effect of Using CBD Placebo Under Stress: Measuring Heart Rate, Mean Arterial Pressure, and Reported Stress Level

Evelynne Morris, Ireland Buckley, Gabbi Marchelli, Dena Quigley, Ph.D.

This experiment studied whether a cannabidiol (CBD) placebo, coconut oil, plays a role in relieving stress. Acting as a stress-inducing stimulus, the Stroop test is a video that requires participants to say the color of the word rather than the word itself when projected on the screen. While administering the Stroop test to a group of college participants ranging from 19 to 21 years of age, change in heart rate and mean arterial pressure were measured using a blood pressure cuff and pulse plethysmograph. Coconut oil, the CBD placebo, was administered to the participant’s temples and neck before repeating the Stroop test. Mean arterial pressure was found to be significantly lower when the participant believed they were using CBD. Heart rate also decreased when the placebo was used. At various intervals during the study, personal surveys asked for the participant’s current stress level on a standardized scale from 1-10 and their view on the given drug. Recorded results displayed a general decrease in indicated stress levels after the CBD placebo was administered. The findings from this study are expected to spike interest in continuing to study the uses and effects of CBD.

Abstract

Introduction

Recent studies focusing on cannabidiol (CBD), a Cannabis sativa constituent, have shown the drug’s powerful effect on treating neuropsychiatric disorders. Specifically, CBD has been shown to possess anti-inflammatory and anti-anxiety properties (Aubrey, 2018). As cannabidiol has increasingly become well-known as a “magic” drug, it is unknown to what extent a psychological factor, the placebo effect, influences the decrease of stress-induced heart rate and blood pressure. By measuring the effect of a placebo in place of CBD, we will learn how influential the placebo effect is at mitigating stress-related symptoms. Evidence has shown that patient expectations about medicines influence how the patient feels after taking medication (American Cancer Society, 2015). The placebo effect can be verbally induced or result from conditioning, as well as prior experiences (Munnangi, 2019). Optimistic expectations lead to a positive response, and negative expectations lead to inhibition of the desired response (Benedetti, 2013). For instance, if someone expects CBD to work, there should be a higher chance that the given CBD placebo will show a decrease in the stress factors of heart rate and blood pressure on a person. This is the main hypothesis being tested in our experiment. We hypothesize that, as a psychological factor, the perception alone of using CBD oil will decrease blood pressure and heart rate in response to a stressful stimulus. In our research, the stressful stimulus is a Stroop test video. In this test, participants had to say aloud the color of the word that they saw flash before them on the screen. As the video progressed, the flashing of words on the screen increased in speed. The final round (Round 4) projected words on the screen at such a high pace that made it difficult to process the word before the next appeared (MindfulThinks, 2017).

Although it does stem from the marijuana plant, the removal of tetrahydrocannabinol (THC) leaves CBD oil with none of the psychoactive components. The use of CBD interacts with several receptors that regulate fear and anxiety, such as the cannabinoid type 1 receptor (CB1R), the serotonin 5-HT1A receptor, and the transient receptor potential vanilloid type 1 (TRPV1) (Blessing, 2015). As part of the endocannabinoid system, CB1R functions as an inhibitory Gi/o protein-coupled receptor that is densely distributed in the basal ganglia. The CB1R involves the cAMP signal transduction pathway. In this pathway, when the ligand binds to the G-protein coupled receptor, the alpha subunit migrates to adenylyl cyclase creating cAMP from ATP. When the CB1R is activated, Gi activates, which decreases intracellular cAMP concentration by inhibiting the production of adenylyl cyclase, the main enzyme used in this pathway (Blessing, 2015). Described as an anxiolytic, CBD has in the past few years been used as a therapeutic drug to combat anxiety disorders and PTSD. By administering CBD, acute increases in heart rate and blood pressure were typically reduced (Blessing, 2015).

Regarding the myocardial physiology, heart rate is determined by the conductive autorhythmic cells in the heart which demonstrate pacemaker activity (Costanzo, 2018). The action potentials travel down along cardiac muscle membrane

and down into the T-tubule. In the T-tubule, a voltage gated channel opens in response to the action potential. The opening of this channel allows calcium to enter into the cardiac muscle cell. The calcium moves into the smooth endoplasmic reticulum and mediates calcium release back out of the smooth endoplasmic reticulum. In the autorhythmic cell, the action potential consists of sodium “funny” channels and T-type calcium channels. Sodium “funny” channels allow sodium into the cell causing the cell to depolarize. T-type calcium channels then open, which causes calcium to enter the cell and depolarizes it even more. The effects of these two different channels create the threshold potential. At threshold, voltage gated L-type calcium channels are activated and opened which results in rapid depolarization as more calcium enters the cell. Finally, the voltage gated potassium channels open and allow potassium to leave the cell resulting in repolarization. After repolarizing, the “funny” channels kick in again and the cycle starts over again. The voltage provided from the autorhythmic cells activate the sodium gated channels in contractile cells. This all leads to contraction of the heart at a regulated pace (Costanzo, 2018). For blood pressure, one needs to take into account the systolic and diastolic pressure. The systole event in the cardiac cycle marks the time where the cardiac muscle is contracting and the blood in the ventricle is ejecting (Costanzo, 2018). In contrast, the diastole event in the cardiac cycle is the time where the cardiac muscle is relaxing and the ventricle is filling with blood. Blood pressure is reported as the systolic pressure over the diastolic pressure. In other words, blood pressure is the peak pressure in the arteries over the minimum pressure in the arteries (Costanzo, 2018).

Materials and Methods

The objective of this experiment was to discern the differences in heart rate and blood pressure measurements in participants who watched a stressful video with and without using a CBD oil placebo. Coconut oil was given as the placebo CBD oil. The 24 subjects observed consisted of 17 females and 6 male Baylor University undergraduates with ages ranging from 19 to 21. Additionally, each individual was placed in both a control group and experimental group.

First, the participants filled out a survey to evaluate their current stress levels and were asked if they had any allergies. A blood pressure cuff was wrapped around the participant’s left arm, a pulse plethysmograph was placed on the participant’s right index finger, and noise cancelling headphones were given to the participant in order to diminish ambient noise. Prior to watching the stressful video, the participant’s resting blood pressure and pulse were measured. A Stroop test video was chosen for the participants to watch. The video included three different levels that each increased in speed. Participants were given instructions to say aloud the color of the word that appeared on the screen rather than the word itself. For approximately one minute, they watched the YouTube video as their heart rate was continuously measured. As soon as the video ended, blood pressure and heart rate were measured for the second time. During the neutral time between video clips, the participants filled out a post-survey regarding their new stress level and conducted a casual conversation with the experimenters. Before showing the Stroop test video for the second time, the participant was instructed to use CBD oil on their temples and back of the neck. No additional information about CBD in general was given. The video then played for one minute as heart rate was continuously measured. Right as the video ended, blood pressure and heart rate were measured for the third time. Afterwards, the participant then completed a final survey evaluating their overall experience and personal view on CBD. This procedure was performed on every individual on each data collection day. Approximately six participants were seen each day, over a span of four trial days. To control for confounding or outside variables, if a participant asked for more information on CBD, we answered with a generic reply stating that it is in a lot of products to avoid any confirmation bias. This allowed us to test each participants response based solely on their previous knowledge of CBD. Three bar graphs were created. The first graph presented data collected from the participants’ survey results on their current stress level. The second graph reported the differences in heart rate. Collected heart rates for all participants were then averaged every 10 seconds using (V1+V2)/2. Finally, the third graph reported the differences in mean arterial pressure (MAP). Collected blood pressure using systolic and diastolic pressure was then calculated using (SBP+ (2×DBP))/3. All three of the bar graphs are split up into the following sections: resting, without CBD placebo, and with CBD placebo. To further analyze the data, two paired t-tests were used in order to observe significance of the change in heart rate and blood pressure between using the placebo and not using the placebo.

Results

All figures are shown on the following page. In Figure 1, the second column (without CBD placebo) is the highest and depicts an increase in recorded stress level between the participants resting and post-Stroop test. At the moment in the experiment marked by the third column (with CBD placebo), participants reported a dramatic decrease in stress level in comparison to their stress level after watching the video for the first time. Unbeknownst to the participants, the “CBD” they applied to their temples was merely a placebo. The coconut oil should have had no effect on the participants, however, the participants still recorded a decrease in stress level. In Figure 2, there is an increase in heart rate in participants from resting to taking the stressful test without the CBD placebo. There was a decrease in heart rate with the CBD placebo, as opposed to without. Since this study is primarily focusing on the placebo effect on the body, we ran paired t-tests using the CBD placebo and without using the CBD placebo. This created an even field where the main differences were personal background and belief about how CBD would affect stress level while performing the same Stroop test. After conducting paired t-tests on heart rate with the CBD placebo and without the placebo, a t-stat value of 4.004 (p-value of 0.05) showed a significant difference between the two. This can also be seen in Figure 2, where using the CBD placebo decreased the average heart rate by about 6 beats per minute. An alternate paired t-test based on mean arterial

Indicated Stress Level 5.4 5.2 5.0 4.8 4.6

4.4 Resting 4.75 Without CBD Placebo

Participant State 5.42

With CBD Placebo 5.00

Figure 1. In each of the three surveys, we asked for the participant’s current stress level on a scale from 1 to 10. This bar graph represents three consecutive surveys: when resting before the Stroop test video, after watching the video without the CBD placebo, and after the second time watching the video when participants were told they were using CBD. All 24 of the participants’ scores were averaged together for each recorded stress level. Individual differences are indicated by the error bars given.

Average Heart Rate (bpm) 100 90 80 70 60 50 40 30 20 0 10

Average Dierences in Heart Rate

76.625

Resting 87.965

Without CBD Placebo Participant State 82.083

With CBD Placebo

Figure 2. The heart rate, measured as beats per minute, for each participant was averaged together among the 24 total participants for each section of the experiment. When resting, heart rate was measured once. When watching the Stroop test video without the CBD placebo and when participants were told they were using CBD, heart rate was measured every 10 seconds and then averaged together. Individual differences are indicated by the error bars given.

Mean Arterial Pressure (mmHg) 93 92 91 90 89 88 87 86 85 83 84

Average Dierences in MAP

90.679

Resting 87.212

Without CBD Placebo Participant State 90.379

With CBD Placebo

Figure 3. The mean arterial pressure (MAP), calculated from diastolic and systolic blood pressure for each participant, was averaged together among 21 of the participants for each section of the experiment. (3 participants’ blood pressures were excluded from data collection because of the blood pressure cuff not working). Blood pressure was measured once for each of the three states: when resting, after watching the Stroop test video without the CBD placebo, and after the second time watching the video using the CBD placebo. Individual differences are indicated by the error bars given.

pressure (MAP) when told they were using CBD compared to without provided an insignificant t-stat of -0.966 (p-value of 0.05). This can also be seen in Figure 3, where MAP actually slightly increased the second time after watching the Stroop test video.

Discussion

Overall, the results support our original hypothesis. As a psychological factor, the perception of using CBD oil decreased heart rate in response to a stressful stimulus. From our statistical findings, there was a significant drop in heart rate once participants took the Stroop test after being told to apply “CBD” to their temples. On the other hand, the statistical data was insignificant regarding the change of blood pressure between taking the Stroop test with and without the CBD placebo. Because we did not see a consistent decrease in blood pressure similar to the decrease in heart rate, we can still conclude that most of our hypothesis was correct. This is because heart rate and blood pressure do not necessarily increase at the same time (American Heart Association, 2019). Healthy blood vessels respond to increased heart rate by dilating to maintain blood pressure. Since our participants reported no health complications, we can conclude that the insignificant change in blood pressure does not truly affect our results. Psychologically, participants felt a difference between taking the CBD placebo as well. From the psychological perception that the participants’ stress levels would decrease, their heart rates also decreased. As this study relied on the placebo effect of CBD, it was shocking to see how many of the college students had little to no knowledge about this substance. Approximately half of the responses given in the final survey were stated as “I do not know what CBD is,” and “I’m unsure of its effects.” Other responses given were “I believe CBD is medically beneficial,” and “I do not know if there is not a lot of data to back up the uses.” Although they had no information about how CBD would affect them, none of the participants refused to use the substance during the trial. One of the participants even believed CBD was the same as THC and weed. This shows the lack of educational programs given about marijuana. In the state of Texas, where laws regarding CBD use are continually passed, it is important that students are educated about this prevailing substance (McGaughy, 2019). Similar in reference to alcohol and other drugs, being uninformed can cause poor decision making. The responses from the final survey revealed that many people did not have any knowledge of CBD. All of the participants were willing to use the product in our experiment even if they knew little information on the substance. Many of the participants did not ask any additional information about the product when we asked them to rub CBD oil on their skin. After observing our participants’ body language and attitudes, every single participant did not even hesitate before administering it to their temples and neck. Only one participant asked a question to clarify if the product was an ingredient in marijuana as she was rubbing the CBD oil placebo into her skin. Because we did not want to affect her perception of the product before completing the experiment, we answered her question very vaguely by not disclosing any additional information. This trend was interesting because we noticed that this attitude towards unfamiliar substances is consistent with many things in society. Many teenagers and young adults try products without knowing the ingredients or the risk factors behind the substance. Using substances without knowledge of its makeup can be dangerous due to allergies, drug interactions, and other side effects. Throughout the experimental trials, we noticed several other trends in our observations. In the beginning, when we asked participants to complete the pre-survey, they seemed slightly anxious about not knowing the experiment. This anxiousness was shown in their preliminary heart rate. As the participant began to relax before we started the first part of the experiment, their resting heart rate became stable. An interesting observation we made was with each individual during the Stroop test video. When the Stroop test began to move at a quicker pace towards the end of the video in Round 4, all of the participants started to laugh. Some participants laughed consistently and did not even attempt Round 4 at all. The point in which everyone started laughing was also when we saw a trend in a rise in blood pressure among all of the participants.

Before starting this study, we tried controlling any outstanding variables or confounding circumstance that would cause deviations in our experiment. Although we tried to prevent these causes, there were sources of error that might have been responsible for small differences in our results. To record each participant’s stress level, we required three surveys to be filled out throughout the experiment. Because we used a selfreporting survey, the variations in actual stress level could have been slightly off compared to what was reported in the survey results. Many times, surveys can cause biased or misleading information to be gathered because participants are not fully honest or fail to report all necessary information. Another source of error could have occurred using the headphones. We decided to use noise-cancelling headphones in our experiment to diminish outside conversations and distractions in the classroom during the stress stimulus, the Stroop test. For the first day, we conducted our experiment using Apple AirPods. Although these headphones kept some noise constant, they did not block out all background noise. For the remaining experimental days, we used Bose noise-cancelling headphones to help control the background noise we found in our first day of experimental study. Because we switched headphones from the first group of participants, there might be a slight variation in the results due to differences in distracting background noise. However, the main source of possible error is rooted in the Stroop test video. We decided to use the same stress stimulus to assure our stress stimuli for each trial were of the same caliber. Because the same video was viewed, there was a possibility that watching the video the second time was not as stressful as the first time because of the familiarity effect. We did, however, choose to continue using the same video because of the specific content in the Stroop test. Because the words in the video move rapidly, a viewer cannot easily remember their specific order to increase results like in other videos. After conducting this experiment, we discussed additional options for research in the future. To strengthen results, another study could be conducted in the same fashion but with a

different stress stimulus. This additional research could confirm the CBD placebo effect by stimulating the participants in a different way and coming to a similar conclusion. Another study could potentially use a different method to measure stress. With more advanced technology, cortisol levels can be compared in saliva testing. These levels of cortisol correlate relatively to the participant’s stress level. By comparing cortisol levels rather than self-reported stress levels, accuracy and precision of the experiment would increase. In accordance to real world applications of our experiment, we concluded that common effects found in CBD can be partially attributed to the patient’s belief in the products abilities. Because our results had some variations, we could not conclude that every participant had felt the CBD placebo’s effects solely from their belief in the treatment. This allowed our group to infer that CBD’s stress-reducing abilities are assisted by the patient’s prior thoughts, making it have a greater and more positive effect overall. Because there has been some controversy over CBD recently due to it becoming a prominent product in the media and in correlation to marijuana, this study is applicable to the topic at hand. Because CBD is relatively new, many people are searching for research that can serve as the foundation to their stance on the product itself. This experiment can serve as a spark for other studies to seek additional information on the overarching controversy surrounding CBD.

References

Anxiety Relief Without The High? New Studies On CBD, A Cannabis Extract. (2018, April 23). NPR.Org. Retrieved October 10, 2019, from https://www.npr.org/sections/ health-shots/2018/04/23/604307015/anxiety-reliefwithout-the-high-new-studies-on-cbd-a-cannabis-extract Benedetti, F. (2013). Placebo and the new physiology of the doctor-patient relationship. Physiological Reviews, 93 (3), 1207–1246. Blessing, E. M., Steenkamp, M. M., Manzanares, J., &

Marmar, C. R. (2015) Cannabidiol as a potential treatment for anxiety disorders. Neurotherapeutics, 12 (4), 825–836. Blood Pressure vs. Heart Rate (Pulse). (2016, Oct 31). Www.

Heart.Org. Retrieved November 17, 2019, from https:// www.heart.org/en/health-topics/high-blood-pressure/thefacts-about-high-blood-pressure/blood-pressure-vs-heartrate-pulse Costanzo, Linda S. Physiology. Elsevier, 2018. Gov. Greg Abbott signs law legalizing hemp production, CBD products in Texas. (2019, June 11). Dallas News. https:// www.dallasnews.com/news/politics/2019/06/11/gov-gregabbott-signs-law-legalizing-hemp-production-cbdproducts-in-texas/ Haapanen, H. (2018, July 3). How to measure stress?

Medium. https://medium.com/inmehealth/how-tomeasure-stress-d770da69152e How Fast Is Your Brain? The Stroop Test. (2017, April 11).

Retrieved March 19, 2020, from https://www.youtube.com/ watch?v=gjesfzWozo4 Munnangi, S., & Angus, L. D. (2020). Placebo Effect. In

StatPearls. StatPearls Publishing. http://www.ncbi.nlm.nih. gov/books/NBK513296/ Placebo Effect. (2015, April 10). Retrieved October 10, 2019, from https://www.cancer.org/treatment/treatments-andside-effects/clinical-trials/placebo-effect.html Placebo Genetics | Project CBD. (2019, May 6). Retrieved

November 17, 2019, from https://www.projectcbd.org/ news/quick-hits/placebo-genetics Studies on CBD and Stress. (n.d.). Retrieved October 10, 2019, from https://www.projectcbd.org/cbd-for/stress What Are the Benefits of CBD? - The New York Times. (2019,

October 17). Retrieved October 20, 2019, from https:// www.nytimes.com/2019/10/16/style/self-care/cbd-oilbenefits.html