Several studies demonstrate that abuse rates for cannabis
are lower than rates for other common drugs. Cannabis use
is usually not problematic use and cannabis users usually
have no social problems which can be attributed to cannabis.
The abuse potential of cannabis is insufficient to justify
prohibition of medical use.
In a sample of 10,641 Australians aged 18 years and older,
2.2% of adults were diagnosed with DSM-IV cannabis use disorder,
comprising cannabis dependence (1.5%) and cannabis abuse (0.7%)
(Swift et al. 2001). In this sample, 21% of cannabis users
met criteria for cannabis dependence and 10.7% for abuse.
Thus, there was a considerable number of cannabis users in
this sample with substance use disorders without being dependent.
In this sample, cannabis dependence was twice as likely to
occur as cannabis abuse.
Most cannabis use is not problematic even for adolescents.
In a survey of 2641 UK school students aged 15-16 years, 201
students reported having used cannabis 40 times or more. They
were examined using cluster analysis and also compared to
"Three clusters of heavy cannabis users emerged. The
smallest was largely distinguished by antisocial behaviour.
Another cluster were clearly unhappy, with little support
from parents and friends, high levels of depressed mood and
low levels of self-esteem. The largest cluster were 'ordinary'
and had little to distinguish them apart from a belief that
their environment was stable and predictable and that society's
rules should be obeyed. Although clear relationships emerged
between heavy cannabis use and heavy use of other substances,
the 'ordinary' cluster of heavy cannabis users were less likely
than the others to have used other illicit drugs. It is therefore
concluded that teenage heavy cannabis users have varied motivations
and contexts for their usage. They should not be seen as a
homogeneous group and many do not appear to use other illicit
drugs" (Miller and Plant 2002).
Often cannabis users are treated as a homogeneous group,
usually when attempting to analyze a correlation with the
use of other drugs, with mental illnesses (depression, schizophrenia),
or to find predictors for a certain development (e.g. Griffin
et al. 2002, Degenhardt et al. 2001a). Degenhardt et al. (2001a)
analyzed relationships between alcohol, cannabis and tobacco
and indicators of mental health problems. Alcohol users had
lower rates of affective and anxiety disorders than non-users
of alcohol, while those meeting criteria for alcohol dependence
had the highest rates. Tobacco and cannabis use were both
associated with increased rates of all mental health problems
examined. However, after controlling for demographics, neuroticism
and other drug use, cannabis was not associated with anxiety
or affective disorders. Alcohol dependence and tobacco use
remained associated with both of these indicators of mental
health. All three types of drug use were associated with higher
rates of other substance use problems, with cannabis having
the strongest association. It should be noted that researchers
differentiated alcohol use and alcohol dependence and found
very different results, while no such differentiation was
made for cannabis.
It is well established that most users of legal drugs, notably
alcohol, tobacco and caffeine, control their use and are not
abusing the drug. It appears from cluster analyses that this
is also the case with cannabis and that studies which do not
use cluster analyses and do not distinguish use from problematic
use will overlook relevant information.
The associations that are found with cannabis have also been
found with legal drugs. Degenhardt and Hall (2001) examined
the comorbidity between tobacco use, substance-use disorders
and mental health problems among Australian adults aged 18
years and over. DSM-IV diagnoses of substance use, anxiety,
and affective disorders were derived using the Composite International
Diagnostic Interview (CIDI). Other measures included a screener
for psychosis and measures of psychological distress and disability.
Researchers found that current tobacco use was strongly associated
with abuse/dependence upon alcohol, cannabis, and other substances,
and with higher rates of anxiety and affective disorders.
Current smokers were more likely to screen positively for
psychosis and reported greater psychological distress and
disability than non-smokers and persons who had never smoked.
These higher rates of other problems were not explained by
differences in demographic characteristics, neuroticism scores,
or by use of other drugs. The authors concluded:
"Current tobacco use is associated with a range of other
substance-use and mental health problems. These are likely
to reduce the success of attempts to quit smoking. The presence
of these other problems needs to be considered when considering
smoking-cessation treatment, and further research may provide
information on more effective treatment strategies for persons
with co-existing substance-use and mental health problems."
Degenhardt et al (2001b) found that psychosis in a sample
of 6,722 Australian adults were associated with the regular
use of tobacco, alcohol, cannabis and opiates.
"Ninety-nine persons (1.4%) screened positively for
psychosis. Regular tobacco, alcohol and cannabis use were
much more common among persons screening positively, as were
alcohol, cannabis and other drug use disorders. Among alcohol
and cannabis users, psychosis 'cases' were much more likely
to be dependent. Ordinal logistic regressions revealed that
regular tobacco use, cannabis and alcohol dependence, and
opiate abuse were predictors of psychosis scores."
For marijuana, even simple associations between an undifferentiated
group of users and commonly believed attributes, for example
that cannabis users are not ambitious in sports or at work,
cannot generally be established. The French Monitoring Centre
for Drugs and Drug Addictions (OFDT) conducted a national
school survey on the relationship between sporting activities
and alcohol, cigarette and cannabis use among adolescents
(Peretti-Watel et al. 2002). Respondents were asked confidentially
by self-administered questionnaire (pen and paper) about their
use of licit and illicit drugs and life-style (including sporting
activities outside school: hours per week, registration in
a club, type of sport).
"FINDINGS: The U-shaped curve between the intensity
of physical activities and licit and illicit drug use appeared
not to be systematic. It depended mainly on the product and
the level of use. It only remained significant for boys and
heavy smoking once gender and age effect were taken into account.
CONCLUSION: The results stress the need to control for age
and gender when the survey participants are teenagers. The
relationship between drug use and sporting activity also depends
on the type of sport" (Peretti-Watel et al. 2002).
One criteria of substance abuse deals with the "failure
to fulfill major role obligations at work, school, or home."
There are several studies dealing with the effects of cannabis
use on school and work performance, with conflicting results.
McDaniel (1988) analyzed the relationship between pre-employment
drug use and on-the-job performance. He found only a small
positive correlation. Blank and Fenton (1989) found a positive
association between positive pre-employment testing for marijuana
and later dismissals. On the other side, Parish (1989) did
not find any relation between pre-employment drug testing
result and performance at work. Normand et al. (1990) did
not find any association between drug test results and subsequent
change in employment. Zwerling et al. (1990) noted a positive
association between cannabis use and change of occupation,
absenteeism and discipline related problems at work. One year
later they reassessed the same cohort and found that there
was no longer an association between cannabis use and absence
from work, while discipline-related problems had decreased
(Ryan et al. 1992). These results from studies that all relied
on results from pre-employment drug testing suggests that
only a minor sub-set of cannabis users suffers from problems
A recent study by Braun et al. (2000) demonstrated that the
cannabis effect is modulated by cultural aspects. This was
a nearly population based study on the prospective interrelationship
of smoking, alcohol intake, marijuana use, and educational
and occupational attainment of black and white young adults.
Researchers used data from the U.S. CARDIA study (Coronary
Artery Risk Development in Young Adults) which involved 5,115
persons 18-30 years of age during the 1985-86 period, who
were reevaluated in 1987/88, 1990/91, 1992/93 and 1995. At
the start of the study, 28.0% stated that they had used cannabis
in the past month. In the following 10 years, cannabis use
was negatively associated with completion of college. However,
this negative association was only found in the younger sub-set
aged 18-24 years at the start of the study, while in the older
sub-set there was only a negative assocation between tobacco
use and college completion. Associations of substance use
with occupational measures were dependent on skin colour.
"In Whites, marijuana use was associated with less prestigious
occupations and lower family income, while smoking was unrelated
and moderate daily drinking was positively associated. In
Blacks, marijuana use was generally unrelated to occupational
measures, while smoking and daily alcohol consumption were
negatively associated" (Braun et al. 2000)
Another criteria of substance abuse deals with "recurrent
substance use in situation in which it is physically hazardous
(e.g. driving an automobile or operating a machine when impaired
by substance use)." Culpability studies provide the best
data on the problems cannabis can cause in the context of
driving. This method studies crashes post hoc based upon information
(usually from coroners and/or police data) about the causative
factors of a crash and blood analyzes on drugs. Examination
of these causative factors permits the researchers to apportion
a score for each crash-involved driver to determine culpability
for the crash. Although there are some differences between
studies, these scores classify each driver as "culpable",
or "not culpable" for the crash. The cases are then
divided into groups according to the results of the blood
analysis. Those drivers who had no detectable drugs in blood
constitute the control group. A recent analyzes summarizes:
"To date (September 1999), seven studies using culpability
analysis have been reported, involving a total of 7,934 drivers.
Alcohol was detected as the only drug in 1,785 drivers and
together with cannabis in 390 drivers. Cannabis was detected
in 684 drivers and in 294 of these was the only drug detected.
Using the culpability analysis method the dominant role of
alcohol in motor vehicle accidents is clearly demonstrated,
confirming the results with the case-control method. Indeed,
in three of the studies outlined in Table 28.2 the concentration-dependence
of alcohol was exhibited. At BAC ?0.1 the culpability ratios
were significant, whereas BAC <0.1 did not achieve significance.
The results to date of crash culpability studies have failed
to demonstrate that drivers with cannabinoids in blood are
significantly more likely than drug-free drivers to be culpable
in road crashes" (Chesher and Longo 2002).
If urine instead of blood is analyzed, predominantly drivers
with regular cannabis use will be found and not those actually
impaired since cannabis use can be detected for some weeks
in the urine of heavy users. In a U.S. study with 414 injured
drivers, 32 of the urine samples were positive for at least
one potentially impairing drug (Lowenstein and Koziol-McLain
2001). Marijuana was detected most frequently (17%), surpassing
alcohol (14%). Compared with drug- and alcohol-free drivers,
the odds of crash responsibility were higher in drivers testing
positive for alcohol alone (odds radio [OR] = 3.2) and in
drivers testing positive for alcohol in combination with other
drugs (OR = 3.5). Marijuana alone was not associated with
crash responsibility (OR = 1.1). In a multivariate analysis,
controlling for age, gender, seat belt use, and other confounding
variables, only alcohol predicted crash responsibility. Researchers
"Alcohol remains the dominant drug associated with injury-producing
traffic crashes. Marijuana is often detected, but in the absence
of alcohol, it is not associated with crash responsibility"
(Lowenstein and Koziol-McLain 2001).
The first controlled, population based study on accidents
on cannabis users compared to non-users was conducted by Braun
et al. (1998) in the U.S. Researchers compared 4,462 individuals
with different cannabis use status (never, former, current
use) with regard to frequency of injuries within three years.
Participants were randomly selected from 64,862 patients of
a health maintenance program aged 15 to 49 years. All injuries
independently of cause and severity were included. A total
of 2,524 accident victims were treated outpatient, 22 were
treated inpatient and 3 were fatalities. There was no association
between cannabis use and injuries.
The abuse potential of a certain substance can also be determined
from the variation in the intensity of use over the course
of several years. A high variability in intensity indicates
a weak potential for dependency and abuse. Von Sydow et al.
(2001) determined incidence and patterns of the course of
cannabis use and disorders as well as cohort effects in a
community sample of adolescents and young adults (n=2,446)
aged 14-24 years at the outset of the study. Patterns of cannabis
use, abuse and dependence (DSM-IV) were assessed using the
Composite International Diagnostic Interview (M-CIDI). They
reported the following results: (1) Cumulative lifetime incidence
for cannabis use (at second follow-up): 47%; 5.5% for cannabis
abuse, 2.2% for dependence. (2) Men used and abused cannabis
more often than women. (3) The majority of the older participants
(18-24 years at baseline) had reduced their cannabis use at
follow-up, while younger participants (14-17 years at baseline)
more often had increased their use and developed abuse or
dependence. (4) The younger birth cohort (born 1977-1981)
tended to start earlier with substance (ab)use compared to
the older birth cohort (1970-1977). (5) Cannabis use was associated
with increasing rates of concomitant use of other licit and
illicit drugs. The authors concluded:
"Cannabis use is widespread in our sample, but the probability
of developing cannabis abuse or dependence is relatively low
(8%). The natural course of cannabis use is quite variable:
about half of all cannabis users stopped their use spontaneously
in their twenties, others report occasional or more frequent
use of cannabis" (Von Sydow et al. 2001)
Felder and Glass (2001) explain that the abuse potential
of cannabis is not sufficient to preclude its medical use.
Their assessment of the relative abuse potential of cannabis
suggests that it does not have the high potential for abuse
required for Schedule I or II status..
Much of the political and public objection to the use of
[Delta]9 THC or marijuana as a therapy centers around its
abuse potential and the belief by some that it serves as a
"gateway" drug leading users to "harder"
drugs of abuse. Many therapeutic drugs have abuse potential,
yet this does not invalidate their role in current therapies.
While there is some preliminary evidence for cannabinoids
activating the reward pathways in the brain (Tanda et al.
1998), most investigators have failed to find addictive or
reinforcing effects of cannabinoids in animal models. Unlike
cocaine or heroin, cannabinoid agonists produce conditioned
place aversion even at low doses (McGregor et al. 1996; Parker
and Gilles 1995) and anxiogenic effects (Onavi et al 1990).
Furthermore, animals will not self-administer cannabinoids
(Harris et al 1974; Leite and Carlina 1974; Cocoran and Amit
1974), and a lack of cross-sensitization between cocaine (McGregor
et al 1995) or amphetamines (Takahashi and Singer 1981) and
cannabinoids has also been demonstrated. (Felder and Glass
A considerable number of cannabis users suffer from problems
that meet the criteria for abuse. However, the large majority
of cannabis users do not experience any relevant problems
related to their use. When compared to legal drugs, abuse
problems with cannabis are generally less severe. The abuse
of cannabis does not preclude its medical use. Relative to
other scheduled drugs cannabis does not have a high potential
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