Cannabis iscommonly referred to as an innocuous drug and the prevalence of lifetime andregular use has increased through time. However, accumulative evidencehighlights the risk of dependence and other adverse effects . It is widelyaccepted that cannabis use can cause mental health issues such asschizophrenia, bipolar and psychosis.

There are approximately 400 chemincalcompounds in an average cannabis plant. The four main compounds within theplant are called delta-9-tetrahydrocannabinol, cannabidiol,delta-8-tetrahydrocannabinol and cannabinol. Each of these compounds arepsychoactive, apart from cannabidiol, the strongest compound beingdelta-9-tetrahydrocannabinol. When cannabis is smoked, its compoundsimmediately enter the bloodstream which is then transported to the brain. (Borgelt,Franson, Nussbaum, & Wang, 2013).

Thedelta-9-tetrahydrocannabinol binding to cannabinoid receptors in the brainresults in the feeling of being ‘high’. A receptor is a site on a brain cellwhere certain substances can stick or bind for a certain amount of time, thiswill then have an effect on the cell, producing nerve impulses. An associationbetween the use of cannabis and the risk of schizophrenia was studied in afollow up of Swedish conscripts. Arguments were raised that this associationwas due to the use of drugs such as cannabis. A dose response relationship wasassessed through the use of cannabis at the age of 18, and schizophrenicdiagnosis 15 years later.

Self reported heavy cannabis users were more likelyto develop schizophrenia 15 years later compared to non cannabis users. However,more than half of these heavy users had a psychiatric diagnosis other thanpsychosis. Very few cannabis users went on to develop schizophrenia whichsuggests that cannabis is most likely to develop schizophrenia with those whoare vulnerable to developing psychosis.

Studies continue to find theassociation between the use of cannabis and the presence of schizophrenia.Zammit et al reported a 27 year follow up study of the Swedish cohort studythat had also found a dose-response relationship between the use of cannabisand the risk of schizophrenia. The link between the use of cannabis and thepresence of schizophrenia persisted when researchers had statisticallycontrolled the effects of other drugs and potential confounding factors whichinclude a history of psychiatric symptoms at baseline. They had estimated thatschizophrenia could have been avoided within 13% of these cases if the usershave prevented the use of cannabis. Zammit et al’s findings were supported in athree year longitudinal study conducted by Van et al.

Van et al had studies therelationship between cannabis use and psychosis with 4, 848 participants inNetherlands. Van et al had found that cannabis use at baseline predicted ahigher change of developing psychotic symptoms during follow up periods in theindividuals who had not predicted these symptoms at baseline. He had found adose-response relationship between the use of cannabis and the presence ofpsychotic symptoms during the follow up periods. Participants who had reportedpsychotic symptoms at baseline were more likely to develop schizophreniacompared to those who were not as vulnerable. These findings suggest thatregular cannabis use predicts an increased risk of developing schizophrenia asthe relationship persists after controlling for confounding variables. The associationbetween cannabis dependence and the presence of psychotic symptoms was examinedon participants between the ages of 18 and 21, controlling for potentialcompound factor such as previous psychotic symptoms.

The findings of this studysuggested that the participants who met diagnostic criteria for cannabisdependence at the age of 18 were 3.7 times more likely to develop psychoticsymptoms compared to those without cannabis dependence. Those who were at theage of 21 were 2.3 times more likely to develop psychotic symptoms compared tothose who were not cannabis dependent.

This study lacks information on thefrequency of cannabis use, therefore it is difficult to assess if heavier dosesor using cannabis for a longer period of time is strongly associated withdeveloping psychotic symptoms. A seven wavecohort study was conducted in the Australian state of Victoria. Theparticipants were randomly selected from two classes within 44 schools drawnfrom catholic, government run and independent schools.

One class from eachschool entered the cohort in the latter part of the ninth school year (wave 1),early in the 10th school year, the second class would enter (wave2). The participants within the study were subsequently reviewed at six monthintervals for the next two years (wave 3 to 6), with a final follow up (wave 7)at the ages of 20-21. Within the waves of 1 to 6, participants used laptopcomputers to self administer the questionnaire, and those who were absent werefollowed up by telephone. The seventh wave of data collected consisted ofcomputer assistant telephone interviews. 1947 of 2032 participants of the study(95.8%) participated at least once during the first six wave.

Clinicalinterview schedules were used to assess depression and anxiety at each wave.The schedule provides data on the frequency, persistence and intrusiveness of14 common psychiatric symptoms. Cannabis use on the basis of self reportedfrequency was assessed in the first six months of waves 1 to 6 and the 12months of wave 7.

This was classified as never used, less than weekly use,weekly use and daily use. 66% of male participants and 52% of femaleparticipants had reported using cannabis at some time. 71 male participants and188 female participants reported depression and anxiety. The prevalence ofdepression and anxiety increased with higher extents of cannabis use. Daily usein female participants predicted higher likelihood of later depression andanxiety. Adolescent cannabis use has been associated with the use of othersubstances and an increase in risk of later drug abuse and dependence. Whilethis affiliation may be attributable to the prolonged use of cannabis,researchers have theorized that this affiliation may be due to the substancesimpact of the developing brain (Jacobus et al, 2009). High rates of participation and the frequent measureduring the participants teenage years draw the strengths of this study.

Possibleexplanations for the high level of anxiety and depression found mainly in thefemale participants may be the effect that the self medicated cannabis has onmental health. Cannabinoid receptors are found widely in the central nervoussystem, with a distribution that is consistent with the brain area that isresponsible for functioning emotion and cognition (Ameri A, 1999).However, thesetheoretical findings differ from studies that use medicinal cannabis in orderto treat schizophrenia.

The complex nature of schizophrenia which includesmultiple brain neurotransmitters leads to the search of effective drugs.  Participants ages 18-50 who had been diagnosedwith schizophrenia were eligible to this study. All 42 participants of thisstudy were inpatients of the Department of Psychiatry and Psychotherapy of theUniversity of Cologne. Participants were hospitalized at baseline and wereassessed for 28 days after random assignment to treatment. 37 of theseparticipants were suffering from acute paranoid schizophrenia and the other 5were initially diagnosed as suffering from schizophreniform psychosis, but werefollowed up and also diagnosed with paranoid schizophrenia after the study hadbeen completed. Participants who had a positive urine drug results for the useof illicit drugs in general and cannabinoids were unable to participate in the studyto avoid the interaction of currently active cannabinoids, includingcannabidiol. The study objective was to determine whether the use ofcannabidiol during the period of 28 days was non-inferior to Amisulpride in thetreatment of patients with schizophrenia.

Antipsychotic patients were selectedto receive 200mg of either Cannabidiol or Amisulpride four times per days, witha total of 800mg daily. The treatment was maintained for 3 weeks. A reductionfrom 800mg to 600mg was allocated to patients who received unwanted sideeffects after week two, which had included three patients in the cannabidioltreatment and five in the Amisulpride treatment. The Positive and NegativeSyndrome Scale was used to measure the assessment of psychotic symptoms atbaseline, day 14 and day 28.

The results of this study suggested thatcannabidiol was as effective at improving psychotic symptoms as well as the Amisulpride.They had found a statistically significant association between the increase inanandamide levels and decrease in psychotic symptoms in patients treated withcannabidiol. These findings suggest that although the use of medicinalcannabinoid can rather decrease the presence of mental health issues such asschizophrenia. This study uses a different administration of cannabidiol asedible routes are now more common.

This reflects more current trends inmarijuana use and looks at different effects it may cause. Aharm-reduction approach to alcoholism was seen to be the substitution ofcannabis. 92 participants were identified as using cannabis to treat alcoholabuse and related problems. Follow up visits, being 12 month intervals wereprovided to the patients in order for them to evaluate their status as“improved”, “stable” or “worse” as well as their efficacy of cannabis from“very effective to “ineffectual”. Twenty-six patients reported the use ofcannabis treating depression, anxiety and stress. Research on self-reportedreasoning for using drugs such as cannabis supports this idea. However it canbe argued that other factors such as peer group influences, poor socialfunctioning and poor social skills could increase the likelihood of mentaldisorders which leads to the use of drugs to find a solution for theirdisorders. (Taylor D, Warner R, & Wright J, 1994).

The self-medicationhypothesis is supported by suggestions from controlled studies that cannabisimproves mood, therefore individuals who are depressed at baseline are morelikely to begin, continue or increase their use of cannabis during follow-upperiods. Also, this study does not assess the amount of cannabis use. There maybe regular users who use a small amount of marijuana, as well as les frequentusers who tend to use a larger amount of cannabis, therefore the amount ofcannabis used would distinguish the effect it would cause.Questionsremain about the level of association between cannabis use and mental healthissues.

Findings have provided conflicting evidence on the association betweencannabis use and depression. A study which had used participants from a primarycare sample had found that among females only, the use of cannabis had doublethe risk of depression (Rowe M, Fleming M, Barry K, Manwell L. & Kropp S(1995).

A study, consisting of 88 high school seniors have found that amongcannabis users, greater suicidal thoughts were arising more compared to thosewho had not used cannabis (Field T, Diego M & Sanders C, 2001). Incontrast, a study which had consisted of 19-21 year olds have found nodifference between light and heavy users in the number of depressive symptoms.With two groups of participants, 45 ‘heavy users’ (used cannabis daily for atleast two years) alongside other illicit drugs and 44 ‘occasional users’(participants who had never used cannabis more than 10 times a month) wereexamined and had reported no significant difference between the groups in ratesof any psychiatric diagnosis (Gruber S, Kouri E, Pope H & Yurgelun T D, 1995).

It is difficult to generalize the findings of these studies as there arelimitations with the measures of cannabis used in the research. The study hadgroups cannabis alongside other illicit drugs, therefore it is difficult tospecify the contribution that the cannabis had made as it is mixed with otheractive drugs within the body. This study does not also compare cannabis userswith non-users, therefore it makes it unclear to distinguish if the cannabiscauses the depression. It isreasonable to conclude that several studies found a consistent increase inincidence of mental health issues in individuals who had used cannabis.

Studiestended to report larger effects of cannabis for more frequent use, as moststudies had showed a 50-200% increase for those who tended to use cannabis on amore frequent level, compared to those who weren’t so frequent. Studies hadused a dose-response effect to observe the relationship between cannabis andmental health. Most of the studies had included people that hadn’t hadpsychosis at baseline as it showed the effect that cannabis had on their mentalhealth. The relationship between cannabis and mental health issues is complex.Many people may use cannabis for its euphoric and relaxing effects, howeverothers may experience feelings such as depression and anxiety when intoxicated.Hallucinations and psychotic symptoms may also be triggered by the use ofcannabis 


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