Essay: The Effects of Chronic Marijuana Usage on Neurocognition and Cognitive Abilities in Adolescents

Abstract
This study seeks to observe the effects of chronic marijuana usage on the neurocognition of adolescents and the extent to which such effects, if any, influence their cognitive abilities. This longitudinal study will analyze various factors, such as: age at onset of usage; frequency of usage, duration of usage; and gender; and whether these factors affect neurocognitive functioning and subsequent cognitive function. In addition, the study will analyze whether the cognitive changes (if any) remain after cessation of using marijuana and, if so, whether the effects on cognition can be reversed by abstinence following heavy usage. In the event that any effects on cognitive functionality can be reversed by abstinence, we wish to establish a correlation between the reversal of these neurocognitive and cognitive changes and time.
Background
Societal views towards marijuana use have significantly changed in the 21st century. Once an illicit drug across all 50 states, legislation has been enacted legalizing marijuana for recreational use for people 21 or older in many states, including Alaska, California, Colorado, Maine, Massachusetts, Nevada and Washington; as many as 17 other states across the United States are expected to follow suit in the near future. Arcview Market Research has estimated that the recreational cannabis market grew 74% in 2014. This staggering increase has earned marijuana the title of the fastest growing US industry, which has attracted a significant amount of investment capital over the past two or three years.
Legislation legalizing recreational marijuana use creates an increased importance on understanding the various effects of marijuana on humans. Despite the recreational marijuana laws allowing for people only 21 years or older to acquire and use cannabis, it is widely assumed that allowing marijuana use for those 21 and older will have a secondary effect of providing adolescents with easier access to marijuana. While the acute effects of smoking marijuana have been well-documented (short-term memory loss, increased appetite, and slower reaction times), the long-term effects on neurocognition and subsequent cognitive abilities are less established among the scientific community due to conflicting methods and results among experiments conducted to date. These conflicting results are attributable to a lack of longitudinal studies and the difficulty of adequately controlling marijuana usage among test subjects. This study seeks to resolve these conflicting views and provide a broader picture of the effects of marijuana usage over an extended period of time.
1. Introduction
Neurocognition is defined as any form of cognition that is associated with the functioning of one or more specific areas of the brain. Neurocognition influences cognitive processes, which together encompass cognition. Cognition encompasses processes such as knowledge, attention, memory, working memory, judgment, reasoning and language. While development of overall brain size is complete at a relatively young age, specific structural and functional changes continue into and beyond adolescence, leading to an increase in cognitive efficiency.
The principal objectives of this study are to determine whether or not permanent neurocognitive, and subsequently cognitive processes, change occurs from using marijuana in adolescent users and, if so, whether any of these changes are more significant in adolescents as compared to adults. Many diverse viewpoints exist on these issues, which vary based on onset age of usage, frequency/quantity and duration of usage, period of abstinence after heavy/long-term usage and gender.
1.1 Onset Age of Marijuana Usage
The principal factor for this experiment is the onset age of marijuana usage and how significantly onset usage age affects neurocognition and cognitive abilities. The most prevalent viewpoint of development psychologists is that those who begin to use marijuana at an earlier age are more susceptible to the longer-term consequences of cannabis toxicity than those with cannabis exposure at a later onset age [1]. This group of developmental psychologists suggests that given the continued neurodevelopment throughout adolescence, adolescents are far more vulnerable than adults to certain neural consequences of heavy marijuana use [2]. Animal models using rats have identified dysfunctional pre-attentive filtering of sensory information, impaired object recognition, and reduced motivation in adolescent rats after prolonged use, while adult controls did not display any neurocognitive behavioral deficits [2]. Studies have also shown that heavy marijuana usage in early adolescence shares a strong correlation with cortical thinning and induction of schizophrenia, particularly in men, whereas heavy marijuana usage in later years did not indicate that strong correlation [3].
In contrast with these findings, another group of developmental psychologists believes that adults are just as susceptible as adolescents to the harmful effects of marijuana use on the human brain. Studies featuring adult subjects have shown changes in higher-order cognitive functioning and neural processes that are more pronounced immediately following THC administration and persist after prolonged cessation of use [4]. Other studies have revealed functional changes across cognitive domains in both adult and adolescent cannabis users [5]. While these studies illustrate that adults are affected just as intensely as adolescents, the studies do not address the onset age of marijuana use in subjects and are not longitudinal. These failures make it difficult to quantify the lasting impact on neurocognition and subsequent cognitive processes made by heavy marijuana use with respect to onset age; it is possible that the effects on cognition might permanent in adolescent users but not adult users. Other, less prevalent groups of development psychologists have alternative opinions. For example, some point to a study concluding that after controlling for potential confounding variables such as alcohol, tobacco, and hard drug use, adolescence-limited users of marijuana were not more likely than users starting in later years or low/nonusers to experience mental health issues in their mid-30’s [6]. This result is significant with respect to neurocognition, as neurocognition has a profound impact on mental health [7]. Unfortunately, however, this study did not assess the cognitive abilities of its subjects.
1.2 Frequency/Quantity of Marijuana Usage
Another factor that is subject for debate with respect to the study is the correlation between frequency of marijuana usage and its effect on neurocognition. Some scholars argue that heavier, more frequent usage of marijuana is more likely to hinder neurocognition and subsequently cognitive processes. One study found that as the number of marijuana cigarettes smoked per week by subject increased, performance decreased on tests measuring executive functioning and psychomotor speed [8]. Other studies have concluded that the quantity and frequency of marijuana usage each has strong implications on the quality of recall memory abilities in adolescents [9]. Another study revealed memory deficits after six weeks of abstinence in adolescents that heavily use cannabis but did not have a long-term history of heavy cannabis use [10].
In contrast with these findings, some scholars argue that heavier frequencies and quantities of marijuana use have the same effects on cognition as light usage of marijuana, or no usage at all. One study found no evidence of long-term deficits in working memory and selective attention in heavy cannabis users after one week of abstinence [11]. It should be noted that this study found that while cognitive abilities are not hindered, subjects displayed altered neurophysiological dynamics in the left superior parietal cortex during working memory processing. Another study concluded that after 28 days of abstinence, former heavy marijuana users did not display any deficits on a series of ten neuropsychological tests [12].
1.3 Permanence of Cognitive Deficits Following Cessation of Marijuana Use
This experiment further seeks to explore the permanence of neurocognitive/cognitive effects (if any) following the cessation of marijuana use. Among the different factors of marijuana usage on neurocognition, this area of study contains the least amount of consensus among scholars. While many studies have revealed cognitive deficits, these studies found difficulty establishing whether these effects were temporary (e.g., due to a residue of cannabinoids in the brain or to acute withdrawal effects from cannabis) or long-lasting and permanent (e.g., due to a neurotoxic effect of long-term cannabis exposure). One group of developmental psychologists believes that abstinence does not reverse the adverse effects of chronic marijuana usage in adolescents. One particular study found that even after four weeks of monitored abstinence, adolescents who regularly smoke marijuana performed poorer on performance tests measuring learning, cognitive flexibility, visual scanning, error commission, and working memory [13]. Another study concluded that while attention and working memory are restored at three weeks of abstinence from marijuana, deficits in decision-making, concept formation and planning remain hindered even after three weeks of abstinence [14].
In contrast to the studies discussed above, some scholars argue that the adverse effects of marijuana use on cognition cannot be found or are insignificant if users abstain from use for a significant period of time. A particular study, which was a twin study to control for differences in genetic vulnerability, failed to find any long-term CNS alterations among heavy marijuana users who had ceased marijuana usage for at least one year [15]. The study is meritorious, but it should be noted that not all subjects in the study had been heavy users in adolescence; some were heavy users who began using marijuana in early adulthood. Another study, using 77 current heavy marijuana users who had smoked cannabis at least 5,000 times in their lives, revealed that after 28 days of abstaining from marijuana usage, very few significant cognitive differences existed between users and controls on the test measures. The authors of this study conclude that cannabis-associated cognitive deficits are reversible and related to recent cannabis exposure, rather than irreversible and related to cumulative lifetime use [16].
1.4 Gender Differences in Neurocognitive Effects among Marijuana Users
The final factor that this study will seek to assess, which is the least studied of all factors by development psychologists, is how gender affects cognition with regards to heavy marijuana usage. A group of developmental psychologists believes that gender has a significant impact on cognitive deficits that result from heavy marijuana use. One study found that despite similar levels of marijuana usage, psychomotor speed and sequencing deficits were particularly more present in adolescent male marijuana users as opposed to adolescent female marijuana users. This study suggests that males are particularly vulnerable to white matter changes leading to slower psychomotor speed [17]. This increased vulnerability would make marijuana usage a greater cognitive risk factor in males than in females. In contrast, other studies reveal that adolescent female users of marijuana experience significant changes in amygdala structure and size relative to their adolescent male counterparts [18]. While the amygdala is not directly responsible for regulating cognitive processes, it is responsible for regulating emotion, which can have a significant influence on cognitive processes [19].
2. Methods
2.1 Basic Subject Requirements
In order to obtain optimal and uncontaminated results, there are a few baseline requirements for every subject that wishes to participate in this experiment. Each participating subject would be required to sign a waiver and release, acknowledging the potential harmful effects that could occur to his/her brain over the course of the experiment and releasing the experimenters from any liability. Subjects who are under the age of 18 would be required to have the wavier and release signed by a parent or legal guardian. In order to incentivize parents to allow their adolescents to participate in this experiment, we will offer monetary compensation to all subjects in the amount of $50 for each cognitive testing session and $1,000 upon full completion of the experiment. In addition to the waiver and release, all subjects must sign a statement that affirms that they have used marijuana less than five times prior to their involvement in the experiment. The goal of this requirement is to ensure that the subjects do not have any significant prior experience with marijuana, as prior usage could skew test results, particularly among the control groups. Subjects must also agree in writing that they will not smoke or ingest any marijuana away from the test site premises during the study so that the conductors of the experiment may accurately measure the quantity and frequency of marijuana usage throughout the course of a given week. In addition, non-marijuana users in the control group will be required to sign an agreement that they will not use marijuana at any point during the experiment, will submit to a urine test once per week and will be subject to random urine tests during the experiment. The urine samples will verify that subjects in the control group (non-marijuana users) are remaining abstinent from marijuana use. Finally, each subject must have a general intelligence quotient (IQ) of 95-105 upon the onset of the experiment. While IQ scores may not be the most indicative test with regards to cognitive functioning, they play a role in determining executive function and will help establish a group of subjects with a similar level of intelligence.
2.2 Marijuana Quality/Quantity
In order to ensure unadulterated results for this experiment, the subjects will receive the marijuana that they will use during the experiment from the testing center. As stated above, all subjects in this experiment will be prohibited from using marijuana outside of the testing premises in order to ensure that the experimenters have appropriately accounted for the quantity of marijuana being used by each particular subject. The testing will be performed in a state where recreational marijuana use is legal, and the marijuana will be purchased from a dispensary with a government-verified retail marijuana license. The purpose behind these requirements is tri-fold. First, we are prohibited by law to purchase marijuana other than from an unverified source. Second, we wish to obtain the quality of marijuana that is currently sold in states where it is legal because, as marijuana continues to be de-regulated/legalized in additional states over the coming years, we presume that a similar quality of marijuana will be sold in marijuana dispensaries in these states as well. Finally, and most importantly, we wish to ensure that the marijuana being used by the subjects is not laced with any other substances (e.g., MDMA, Cocaine, PCP). While it is extremely rare for marijuana to be laced with these substances when purchased from unverified retail sellers, there are documented cases in which unverified retail sellers sold marijuana containing these substances. By purchasing the marijuana used in this study from a verified retail seller, we will ensure the safety of our subjects and the transparency of our results.
2.3 Subject Demographics
The demographics of our subjects will vary significantly as there are several factors that we wish to study in this experiment. The first significant factor in our experiment is onset age of marijuana usage. There will be six age groups: 14, 15, 16, 17, 18 and 25. In order to be included in a certain age group, a subject must be within three months of this/her birthday for that age. (Example: A subject that is 14 years and 10 months of age will be placed in the age 15 group, despite not having reached his/her 15th birthday.) Based on our research, adolescents begin using marijuana as early as age 12 [20]. Despite this evidence, frequent usage of marijuana at this age is actually extremely rare, and we deemed it immoral to expose possibly pre-pubescent children to potentially permanent altered neurocognition and cognitive abilities. We deemed age 14 to be an adequate age to begin testing, as this is typically the age in which an adolescent enters high school and is most susceptible to peer pressure to try marijuana [21]. We then chose the subsequent ages of 15-18 because previous studies have shown age 17 to be the critical age with respect to the effects of marijuana on the adolescent brain, with adolescents frequently using marijuana before the age of 17 having significantly more neurocognitive changes than adolescents frequently using marijuana after the age of 17 [1]. Finally, we decided to incorporate a 25-year-old age group into our study, based on the rationale that while some studies have shown that age 17 is the critical age with respect to marijuana effects on the adolescent brain, other studies have shown that an adolescent’s brain maturation continues well into their 20’s [22]. We hope to display that the effects of marijuana usage on this age group will be significantly less radical than on the younger age groups.
Gender will also be an important element to study in this experiment. As a result, we determined that each age group will be split 50% male and 50% female in order to adequately observe the effects of gender on neurocognition and subsequent cognitive abilities.
2.4 Basic Experiment Outline
Subjects will be divided into different groups of study based on age, gender, duration of usage, and frequency/quantity of marijuana used per week. The division of groups based on these criteria can be found on Table 1 on page 21. The duration of usage and quantity used per week will be randomly assigned. Quantity will be measured by “joints,” a common term for a marijuana cigarette. Each marijuana cigarette will contain one gram of marijuana. For example, a subject who smokes four “joints” weekly will be smoking four grams of marijuana per week. The total duration of the experiment for each subject will be ten years. Subjects in the experimental groups (subjects that are using marijuana) will be required to visit the testing center in order to smoke their assigned quantity of marijuana. Subjects will NOT be allowed to smoke more than one “joint” per day. (Example: A subject that is required to smoke four “joints” per week will be required to come and smoke four separate times per week on four separate days.) Each subject will be required to undergo tests that measure cognitive abilities on several occasions: before the subject begins marijuana usage; once every six months during the subject’s marijuana usage; and once every six months in the five subsequent years succeeding his/her marijuana usage. While performing these cognitive abilities tests, the subjects’ neurocognitive activity will be monitored by a Functional Magnetic Resonance Imaging (fMRI) machine. Subjects will be required to abstain from marijuana for at least 12 hours prior to cognitive testing and will be strongly encouraged NOT to perform cognitive tests outside the testing premises as these exercises could potentially improve their cognitive abilities and skew results.
2.5 Cognitive Abilities Tests
As stated above, all subjects will be tested on cognitive abilities while an fMRI machine monitors neurocognitive activity every 60 days for a period of ten years. Set forth below is a description of the cognitive tests that will be performed on all subjects.
2.5.a Recognition Test
An experimenter will list 50 words for the subject at a moderate pace of one word every four seconds. Following a five-minute intermission, the experimenter will list 50 words again. During the second session, the experimenter will list 25 words that were mentioned in the first session, and 25 words that were not mentioned in the first session, but sound similar to a word mentioned in the first session. (Example: “Book” is listed in the first session, and “Look” is listed in the second session.) An on- looking experimenter will record the number of correct responses and average subject response time.
2.5.b Recall Test
A screen will display five objects of varying shape and color for ten seconds. Following a 30 second resting period, the subject will be asked to recall the specific shape, color and location of the five objects. Subjects will perform three rounds of this test. An on-looking experimenter will record the number of correct responses. A response that contains the proper shape, color and location will be considered a correct response.
2.5.c Judgment Test
The subject will view a screen displaying two similar images, with ten slight variations. The subject will be asked to identify the variations by clicking on the location where the variation exists on both images. An on-looking experimenter will record the number of variations that were correctly identified by the subject. A second on-looking experimenter will record the amount of time it takes the subject to identify the ten variations. Subjects will perform three rounds of this test.
2.5.d Attention Test
Subjects will be shown a five-minute informational video. The video clip will contain a faint background noise intended to break the subject’s concentration. An on-looking experimenter will record the number of times the eyes of the subject divert away from the screen. In addition, subjects will take a ten-question quiz at the end of the video which tests them on the content of the informational video. An on-looking experimenter will record the number of correct/incorrect responses and the average completion time of the quiz.
2.5.e Inductive Reasoning Test
Subjects will be shown a sequence of numbers or shapes with a pattern, and then will be asked to extrapolate the next number or shape in the pattern in the sequence. Subjects will perform this exercise for ten rounds. Unbeknownst to the subject, an on-looking experimenter will record the response time as well as the number of correct responses. An example of this assessment can be found in Figure 1.
Figure 1. Inductive Reasoning Test. Subjects will be asked to complete a sequence of numbers or shapes. In this figure, the subject would be required to draw a square within a triangle in order to achieve a correct response.
2.5.f Basic Short Term Memory Test
Subjects will be asked to recall ten basic actions/events that have occurred recently. Subjects will be questioned on personal actions/experiences, such as what they ate for breakfast that morning or dinner last night, the last person they were with before entering the test center, or yesterday’s weather. Response times will be recorded and averaged per subject. An on-looking experimenter will also record responses such as “I don’t remember” and “I’m not sure.”
2.6 Method for Determining Results
As described previously in section 2.5.a-f, an on-looking experimenter will record the results of each cognitive assessment. Based on the recorded results, a “Cognitive Assessment Score” will be determined for each subject for each occasion on which he/she was assessed. The recorded results that will be used to determine the “Cognitive Assessment Score” can be found in Section 2.5. Using the resulting Cognitive Assessment Scores, we will run a linear regression using the following independent variables: age of onset of marijuana usage, frequency of marijuana usage, total duration of usage and gender. The relationship of these independent variables with respect to the dependent variable of their “Cognitive Assessment Score” will be assessed to a significance of p= .055. Neurocognitive effects will be assessed as well. fMRI will reveal differences in brain structure and function among subjects. By the conclusion of our study, explicit files will be compiled on each individual subject, containing fMRI images from each testing session.
Predicted (and Alternative) Results
3.1. Predicted Effects of Onset Age of Marijuana Usage
Based on pre-existing literature, we predict that a younger onset age of marijuana use will lead to more neurocognitive changes and subsequent cognitive deficits in a subject. The majority of literature suggests that subjects ages 17 and under will undergo the most significant changes. We also predict that age will negatively correlate with the permanence of cognitive deficits in subjects. In summary, we predict that younger onset age of marijuana usage will result in a higher level of cognitive deficit and greater permanence of cognitive deficit.
Possible Alternative: A younger onset age of marijuana usage will lead to more cognitive deficits, but the permanence of these results will be uniform across all ages.
Possible Alternative #2: A younger onset age of marijuana usage will lead to a similar level of cognitive deficits across all ages, but these deficits will have greater permanence among the younger onset users.
Possible Alternative #3: The cognitive abilities of subjects will remain relatively uniform across all ages, but greater neurocognitive changes will negatively correlate with onset age of usage.
3.2. Predicted Effects of Quantity of Marijuana Consumed
Based on previous studies, we predict that frequency and quantity of marijuana used will positively correlate with the number of neurocognitive changes and level of cognitive deficit observed. We do not believe that heavier quantities of marijuana consumed will lead to greater permanence of cognitive deficits.
Possible Alternative #1: Changes in neurocognition and subsequent changes in cognitive abilities will not be significant with respect to the frequency and quantity of marijuana consumed.
Possible Alternative #2: Higher frequency and heavier quantities of marijuana consumed will result in more significant neurocognitive changes, but cognitive abilities will not be compromised.
Possible Alternative #3: Higher frequency and heavier quantities of marijuana consumed will not be significant with respect to neurocognitive/cognitive change, but will be significant with respect to the permanence of neurocognitive/cognitive change.
3.3. Predicted Effects of Total Duration of Marijuana Consumption
Based on previous studies, we predict that longer duration of marijuana usage will not be significant with respect to the level of cognitive deficits observed, but will reveal a significant correlation with the permanence of such cognitive deficits. For example, a subject who uses marijuana once a week for five years will suffer more cognitive deficits during the five year period after cessation of marijuana usage as opposed to a subject who uses marijuana once a week for six months.
Possible Alternative #1: Duration of marijuana consumption shares a strong positive correlation with level of cognitive deficits observed AND permanence of these cognitive deficits.
Possible Alternative #2: Duration of marijuana consumption shares a strong positive correlation with level of cognitive deficits observed, but has no significant effect on the permanence of these deficits.
Possible Alternative #3: Duration of marijuana consumption shares a positive correlation with neurocognitive changes, but does not share a correlation with changes in cognitive abilities.
3.4 Predicted Effects on Marijuana Usage with Respect to Gender
Based on previous studies, we predict that male subjects who use marijuana will undergo more neurocognitive changes than their female counterparts, particularly with respect to their levels of white matter. As a result, we expect male marijuana users to experience more cognitive deficits relative to female subjects.
Possible Alternative #1: Males experience more neurocognitive changes than their female counterparts, but no significant cognitive deficits will be observed with respect to gender.
Possible Alternative #2: No significant neurocognitive or cognitive differences are observed with respect to gender.
Possible Alternatives #3 and #4: Our prediction or alternative #1 is observed, but female subjects experience more neurocognitive changes and/or deficits than the male gender.
4. Conclusion/Significance
4.1 Conclusion
By performing this experiment, we hope to obtain data on an increasingly more prevalent issue in society that elicits various conflicting opinions in our society. This longitudinal study seeks to establish how factors such as age at onset of marijuana usage, frequency/quantity and duration of marijuana usage, and gender impact neurocognitive functioning, and subsequently cognitive function and abilities. We predict that earlier onset age of marijuana usage will lead to more significant and permanent cognitive deficits. In addition, we predict that higher frequencies and quantities of marijuana usage will correlate with higher levels of cognitive deficits. We also believe that longer duration of marijuana usage will correlate with more prevalent permanence of cognitive deficits. Finally, we believe that males will experience more neurocognitive changes and subsequently more cognitive deficits than their female counterparts.
4.2 Significance of This Study
The results of this study could have potentially major legislative repercussions in the United States, at both the federal and state levels, as well as internationally. In the event that major neurocognitive changes and cognitive deficits are observed in earlier onset users of marijuana, these results could cause legislators to enact stricter penalties for providing/selling marijuana to minors not only in states in which marijuana is legal for recreational use, but also in states in which it is illegal. In the event that permanent cognitive deficits are observed across any age group, these results could potentially halt or lessen the current push to legalize marijuana in the United States and/or lead to a repeal of legislation enacted and/or referenda approved in states in which recreational marijuana use is legal. In the event that heavier quantities of marijuana usage are observed to lead to more significant and more permanent cognitive deficits, further legislation could be enacted limiting the quantity of marijuana that can be acquired at dispensaries in states in which the sale and use of recreational marijuana is legal. Finally, in the event that significant cognitive deficits are observed with respect to gender, these results could dictate different and more focused educational methods in anti-drug programs, such as D.A.R.E and CADCA.
6 months 1 year 2.5 years 5 years
No smoke (Control) Age 14: 4 subjects
Age 15: 4 subjects
Age 14: 4 subjects
Age 17: 4 subjects
Age 18: 4 subjects
Age 25: 4 subjects Age 14: 4 subjects
Age 15: 4 subjects
Age 14: 4 subjects
Age 17: 4 subjects
Age 18: 4 subjects
Age 25: 4 subjects Age 14: 4 subjects
Age 15: 4 subjects
Age 14: 4 subjects
Age 17: 4 subjects
Age 18: 4 subjects
Age 25: 4 subjects Age 14: 4 subjects
Age 15: 4 subjects
Age 14: 4 subjects
Age 17: 4 subjects
Age 18: 4 subjects
Age 25: 4 subjects
1 “Joint” per week Age 14: 4 subjects
Age 15: 4 subjects
Age 14: 4 subjects
Age 17: 4 subjects
Age 18: 4 subjects
Age 25: 4 subjects
Age 14: 4 subjects
Age 15: 4 subjects
Age 14: 4 subjects
Age 17: 4 subjects
Age 18: 4 subjects
Age 25: 4 subjects Age 14: 4 subjects
Age 15: 4 subjects
Age 14: 4 subjects
Age 17: 4 subjects
Age 18: 4 subjects
Age 25: 4 subjects Age 14: 4 subjects
Age 15: 4 subjects
Age 14: 4 subjects
Age 17: 4 subjects
Age 18: 4 subjects
Age 25: 4 subjects
2 “Joints” per week Age 14: 4 subjects
Age 15: 4 subjects
Age 14: 4 subjects
Age 17: 4 subjects
Age 18: 4 subjects
Age 25: 4 subjects Age 14: 4 subjects
Age 15: 4 subjects
Age 14: 4 subjects
Age 17: 4 subjects
Age 18: 4 subjects
Age 25: 4 subjects Age 14: 4 subjects
Age 15: 4 subjects
Age 14: 4 subjects
Age 17: 4 subjects
Age 18: 4 subjects
Age 25: 4 subjects Age 14: 4 subjects
Age 15: 4 subjects
Age 14: 4 subjects
Age 17: 4 subjects
Age 18: 4 subjects
Age 25: 4 subjects
4 “Joints” per week Age 14: 4 subjects
Age 15: 4 subjects
Age 14: 4 subjects
Age 17: 4 subjects
Age 18: 4 subjects
Age 25: 4 subjects Age 14: 4 subjects
Age 15: 4 subjects
Age 14: 4 subjects
Age 17: 4 subjects
Age 18: 4 subjects
Age 25: 4 subjects Age 14: 4 subjects
Age 15: 4 subjects
Age 14: 4 subjects
Age 17: 4 subjects
Age 18: 4 subjects
Age 25: 4 subjects Age 14: 4 subjects
Age 15: 4 subjects
Age 14: 4 subjects
Age 17: 4 subjects
Age 18: 4 subjects
Age 25: 4 subjects
7 “Joints” per week Age 14: 4 subjects
Age 15: 4 subjects
Age 14: 4 subjects
Age 17: 4 subjects
Age 18: 4 subjects
Age 25: 4 subjects Age 14: 4 subjects
Age 15: 4 subjects
Age 14: 4 subjects
Age 17: 4 subjects
Age 18: 4 subjects
Age 25: 4 subjects Age 14: 4 subjects
Age 15: 4 subjects
Age 14: 4 subjects
Age 17: 4 subjects
Age 18: 4 subjects
Age 25: 4 subjects Age 14: 4 subjects
Age 15: 4 subjects
Age 14: 4 subjects
Age 17: 4 subjects
Age 18: 4 subjects
Age 25: 4 subjects
Table 1. Subject Grouping. Columns indicate duration of marijuana usage, while rows represent quantity of marijuana consumed per week. Each subgroup (four subjects) will have two males and two females. A total of 480 subjects will be required.
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