Ana Radovic

MPHP 439



Epidemiology: Use and Demographic Trends


                Marijuana is the most consumed illegal substance in the United States.  Political measures and changes in legal enforcement along with prevention campaigns are some of the contributors to why rates have varied in different age groups and other demographic categories.  An important point to make is that these rates are difficult to measure because they mostly depend on surveys and personal admittance of using illegal drugs.  Even so, it is clearly evident that throughout recent history, marijuana has consistently been a favored illegal substance of abuse. 




American youth in the ‘70’s used marijuana in high numbers, up to 60% of 12th graders in 1979 had tried the drug.  In 1992, that number fell to 33% and then rose again to 50% in 1997 (23).  These rates have leveled off and currently, according to the 2004 University of Michigan’s 27-year Monitoring the Future Survey, a continuing study of American youth, 46% of 12th graders had tried marijuana.  Although use has decreased since the liberal movements in the ‘60’s and ‘70’s, today’s marijuana is up to 5 times as potent as the marijuana used back then, and therefore may pose greater risks to today’s adolescents (23). The risk for cannabis dependence is lower for adolescents who start using at a younger age (13). 




            In 2003, the National Survey on Drug Use and Health (NSDUH) showed that more than 40% of Americans age 12 and older had tried using marijuana (23).  During a 1999 meeting of the Community Epidemiology Work Group which tracks effects of drug abuse in different U.S. cities, rates for problems associated with marijuana abuse had risen.  These problems included numbers of Emergency Department visits related to marijuana use (5).  When looking at current rates of use, in 2000, 9% of Americans had smoked marijuana in

the previous year, 5% had smoked in the previous month, and less than 5% were using every week (7).





            Rates of marijuana use vary between different races and genders, and not only in different age groups.  Among adolescents, male and Hispanic students showed higher rates of drug use on school grounds, than female and white students (9).  Different countries show different rates of use as well.  In a study of 31 countries, lifetime cannabis use was highest in Switzerland for males (49.1%) and lowest for males and females in Macedonia (2.5% each).  Canadian males and American females exhibited the highest frequent use of marijuana, 14.2% and 5.5% respectively.  This study showed that life-time prevalence and frequent use were associated with per-capita personal consumer expenditure, peer culture (apparent availability of drug), and drug climate (older user community) (2).  Different rates have consistently been seen in men vs. women.  A Johns Hopkins University scientist, Dr. James Anthony, argues that this difference is not due to inherent differences between the genders, but that it is due to different rates of the opportunity to use drugs.  He claims that once that aspect is normalized – the opportunity to use drugs – rates for men and women are the same (35).


Marijuana as a Substance




Lung Effect


            Studies show that individuals involved in chronic marijuana use show the same kinds of respiratory symptoms as tobacco smokers.  These include coughing, wheezing, and bronchitis (38).  Smoking tobacco at the same time therefore may have even increased risks for lung problems, but another downside is that marijuana has been shown to make quitting tobacco more challenging (10).  One study showed that employees who smoke marijuana miss more days of work and report increased health problems, mostly due to respiratory illnesses (23). 










            Just as marijuana shows similar respiratory changes as tobacco, it also shows similar cellular changes in the bronchial tract which are pre-cancerous (138).  These similar changes are for regular marijuana use and regular tobacco use.  Regular marijuana use is defined as a smaller amount smoked than regular tobacco use, which implies that marijuana is in fact more damaging to the respiratory tract than tobacco (34).  Also, the carcinogenic hydrocarbons found in marijuana smoke are 50 to 70% greater than in tobacco smoke (23).  These changes increase the tendency to develop lung cancer, and imply that marijuana may pose as a similar or greater risk factor than tobacco although more epidemiological evidence is needed.

                Marijuana has been shown to increase cancer of the head and neck in some studies.  Dr. Daniel Ford of Johns Hopkins University argues that the only supportive evidence for this relationship was derived from small and likely flawed case-control studies.  He cites research his group conducted from 1994 and 1999 of a large case-control study that lifetime use of marijuana was not associated with cancer (15).  On the other hand, Dr. Zuo-Feng Zhang and colleagues cite a case-control study conducted at the Memorial Sloan-Kettering Cancer Center between 1992 and 1994.  This study showed that marijuana use was a risk factor for squamous cell carcinoma of the head and neck for people younger than 55.  Also, the study showed a dose-response relationship (15).  Clearly, more work needs to be done to appreciate whether there is a true risk involved with marijuana for head and neck cancer. 

                Studies also show that marijuana may increase the risk of transitional cell carcinoma, a cancer found mostly in the bladder (6).  This was seen for men aged less than 60 years.     


Cognitive Effects


            Marijuana use is often associated with memory loss and learning disabilities.  Various studies have been done to prove or disprove this correlation.  Differences occur between effects of acute marijuana use and chronic long-term use on cognition.

                Studies on acute effects show that what is most likely affected is distance and time perception (time seems to lengthen and distance seems to increase between objects), vision (more difficult to discriminate colors), complex reaction time, recognition memory,

and recall (7).  In summary, simple tasks are not affected but more complex tasks, especially those requiring rapid thinking are.


Rats that are exposed to THC, the active ingredient in marijuana, have less of an ability to use short-term memory.  These same effects are seen in rats that have a part of their brain destroyed in the hippocampal region which is involved in short-term memory (23). 

                Studies on chronic use showed less gross effects on neuropsychological impairments such as those seen with alcohol abuse, but some highly sensitive tests show difficulty in transferring information from short-term memory to long-term memory (7).  A very well-controlled study showed differences in brain waves in chronic marijuana users when performing difficult tasks.  These users could not process information as rapidly (31).

                Other studies demonstrate learning deficits in heavy users of marijuana, but often these cognitive abilities can be regained after abstinence (26).  A meta-analysis showed that long-term use was not associated with generalized neurocognitive decline except for a small decline in the capability of learning new information (12).

                There are important differences seen in the adolescent age group in terms of cognition.  One study showed that adults who began smoking marijuana before age 17 had smaller brains, a lower percentage of gray matter – which is the substance of the brain, and a higher percentage of white matter – which is the conducting system of the brain, than adults who had not (36).  Another study showed that someone who begins smoking at age 13 will earn less money and will have completed less education as a young adult (8).  This could possibly be associated with deficits in cognition.  Marijuana use may impact brain development in a critical period, and that suggests that adolescents using marijuana should have more targeted precautions for use. 


Immune System


            Mice exposed to THC were shown to have an impairment of immune function which reduced their ability to slow tumor growth and fight infections (27).  More research is needed to determine whether marijuana reduces the same capabilities in humans.


Heart Attack/Stroke


                Acute effects of marijuana include an increase in heart rate and blood pressure.  One study shows that the risk of heart attack immediately after smoking marijuana is four times greater.  This is especially significant for older individuals who have an increased risk




of a cardiovascular event such as heart attack or stroke due to age.  A review of studies on

cardiovascular risks of cannabis showed that in fact the cardiac effects of marijuana do not pose a risk for young otherwise healthy individuals, but do for older people (19). 


Risks with pregnancy


            There are specific risks which have been associated with marijuana use during pregnancy.  Neonates of women using marijuana develop certain characteristics which reflect possible problems in neurological development.  Young children grow to more often experience symptoms of inattention and impulsivity associated with Attention Deficit Hyperactivity Disorder (ADHD), and also some deficits in learning and memory (18). 

                Marijuana has also been shown to decrease fertility in men by decreasing the effectiveness of sperm in fertilizing an egg (29).


Emergency Department/Accidents


                In 2000, Iversen reported that there had been no deaths from THC overdose.  Animal studies show that an extremely high and improbable amount of joints would need to be smoked in order to achieve toxic levels.  Nonetheless, marijuana is still a somewhat frequent factor involved in emergency visits.  In 2002, marijuana was a contributing factor in 15% of ED visits in 12–17 year olds for unspecified causes (33).  Certain studies show that 6-11% of fatal accident victims test positive for THC but they often test positive for alcohol as well.   




            The National Highway Traffic Safety Administration advises against driving while under the influence of marijuana.  A study they conducted showed that marijuana impaired driving performance, but especially when combined with alcohol, showing a greater effect than alcohol alone (25).  On the other hand, lab studies show that marijuana users compensate for driving inadequacies by driving slower and keeping a greater distance between cars so that they are less likely to cause an accident and epidemiological studies confirm this (1).  This compensation though may not be sufficient when rapid thinking is needed in a driving situation, and as described in the section on cognition, rapid thinking is impaired under acute intoxication.             





Mental Health Damage


            Marijuana abuse has frequently been associated with depressive and even psychotic symptoms but it is often unclear as to whether these mental health disorders are caused by marijuana, self-medicated by marijuana, or are explained by outside factors.  Marijuana intoxication can produce behaviors that are schizophrenic in nature, but these behaviors go away after acute use (14).  One review claims that studies do point to an association between psychosis and marijuana use and proposes a biological explanation, referencing studies which show increases in psychosis not explained by other factors (13).  Another explanation may be that people with mental illnesses self-medicate with marijuana.  A New Zealand study showed that people with mental illness are 15 times more likely to use marijuana at age 18 (7).

                Other studies show associations with depressive symptoms, defined by a certain amotivational syndrome, where individuals do not achieve the same educational and behavior goals as others with similar characteristics.  Research shows that there are not differences in school performance in college students who use and don’t use marijuana (38), but that high school students who use marijuana have lower grades, quit school more often, and spend less time on homework (20).  A causal relationship is refuted by a study that shows poor school performance prior to initiating marijuana use (30).  There may be a reason explaining both poor school performance and increased marijuana use and this reason could possibly be increased deviant behavior.  These individuals may have oppositional defiant disorder, associated with breaking the rules.  Because marijuana is illegal and easily accessed, it may just represent another rule that can be broken.

                A job-related study supports amotivational syndrome.  Workers who smoke marijuana have a 75% increase in absenteeism.  Also of note is a 55% increase in industrial accidents and 85% increase in injuries on the job (23). 

                When controlling for income and family of origin, one study found that marijuana users were less likely to complete college and were more likely to have an income of less than $30,000 than their peers.

                Another correlation with depressive symptoms is demonstrated by a study which showed that people who smoke marijuana before the age of 17 are 3.5 more likely to attempt suicide as those who start later.  Also, the same study showed that marijuana dependent individuals have a higher prevalence of major depressive disorder (22).  As stated before for psychotic symptoms, the causal relationship is unclear.




            Sometimes marijuana use can lead to dependence and problems with addiction.  Dependence according to the DSM-IV, the diagnostic manual of psychiatrists, dependence requires 3 of 7 symptoms in the same year.  These symptoms include tolerance, withdrawal, using more than intended, being unable to cut down, increasing the time spent using, giving up other life activities, and using despite consequences.  The 2003 National Drug Use and Health (NSDUH) study reports that 4.2 million Americans are dependent or abusing marijuana (23).  Of 42,000 people surveyed in a 1998 study, 23% were diagnosed with abuse and 6% were diagnosed with dependence.

                 Marijuana smokers do experience withdrawal symptoms, although often these are not as physical as those for other illicit drugs such as cocaine and heroin.  These withdrawal symptoms include irritability, a depressed mood, lack of appetite, cravings, anger, and restlessness.  These symptoms can be as severe as tobacco withdrawal (4).




                People sometimes associate marijuana with aggressive behavior.  In fact, laboratory test show that an increased THC level does not increase competitive behavior in test subjects (24), although sometimes withdrawal symptoms may include aggression (21).  The 2002 National Institute of Justice’s Arrestee Drug Abuse Monitoring Program found that of arrested individuals, 41% of males and 27% of females were found to test positive for marijuana (7).  This may not point to a causal relationship since many of the same people tested positive for other illicit drugs or alcohol.  A NIDA Research summary provides evidence which supports that often marijuana is combined with other illicit drugs, and this may contribute to the aggressive behavior.




                A highly debatable topic is whether or not marijuana is a gateway drug, or a drug which once initiated, leads to the use of other drugs, which are often more harmful and addictive.  Data from the Substance Abuse and Mental health Services Administration in 2000 showed that of those who have tried marijuana, 77% have tried crack, 33% have tried cocaine, and 3.9% have tried heroin.  Although most users of hard drugs try marijuana first, most of marijuana users do not try hard drugs (7).  There are different explanations for why these associations exist.  One is that users of marijuana, by virtue of marijuana being an


illegal drug, will also be exposed to a market of other illegal drugs, which is less likely for someone who abuses alcohol or tobacco, which are legal.  Another explanation is that some marijuana users exhibit deviant behavior which motivates them to abuse illegal substances and therefore influences the use of both marijuana and other illicit drugs.  Another theory is that there may be pharmacological effects associated with marijuana use which increase the likelihood of use of other illicit drugs.  An experiment performed in 1997 demonstrated that rats exposed to THC did not show a greater propensity to push levers for other drugs (28).  On the other hand, a dose-response relationship was found by researchers correlating the amount of marijuana use at age 16 with alcohol and other substance use by age 18 (13).  One paper suggests that animal studies which show similar neurological effects of cannabis and cocaine and heroin suggest that use of one may influence the use of another (13).   




Treatment Techniques


                Project MATCH, a 1998 comparative study of cognitive behavioral therapy, 12-step facilitation, and motivational interviewing showed that all three treatment approaches showed comparable effectiveness in treating marijuana addiction.  The author of the study cited previously on effects of withdrawal suggests that marijuana abusers trying to quit should be informed of what to expect in terms of withdrawal symptoms in order to normalize the process and treat some of the symptoms involved in order to decrease the likelihood of relapse (4).  Another author previously cited when discussing increased rates of suicide and depressive symptoms associated with marijuana use, argues that although a causal relationship is unclear, what is clear is the likelihood for other mental disorders in a marijuana abuser and it is important for those to be addressed at the same time as the addictive symptoms (22).

                One possible treatment option that is not available yet is medication.  Some illegal drug use is able to be medicated by drugs which conflict with the actions of the illicit drug and therefore either reduce the response, or produce an undesired response in order to reduce the desire to use the illicit drug.  One drug currently being studied called SR141716 shows the same effects for marijuana, and blocks the receptors which marijuana binds to in humans (17).  This development poses new options for abusers of marijuana who require treatment.         



Treatment Programs


                Some research shows that outpatient interventions associated with social support show some of the best improvements in marijuana addiction (7).  Other research demonstrates the effectiveness of voucher programs, where individuals are compensated with gifts for abstaining from drug use (3).  In 2001, an evaluation of 23 community-based adolescent treatment programs found a decrease from 80% to 44% of weekly marijuana use, fewer thoughts of suicide, higher self-esteem, and better school performance (16). 




            The aforementioned risk of marijuana use specifically associated with adolescents emphasizes the need for preventive efforts against early use and any time abuse of marijuana.  Educational programs such as the well-known police enforced DARE program have been shown to be ineffective.  The best preventive methods employ social influence such as changing social norms so that individuals understand the reality of the drug environment and that not “everyone is doing it”, teaching drug refusal skills, and using cognitive behavioral skills to make decisions based on pros and cons (7).  In rural Iowa public schools, short-term family prevention programs have shown to produce long-term effects in marijuana and tobacco and alcohol abstinence.  New marijuana users four years after the intervention were 2.5 times more prevalent in the control group than in the group participating in the program (32).  This evidence supports the notion that a social support approach would be most effective in preventive programming.

















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