Cannabis dependence: predictors, course and treatment seeking

In the Netherlands, it is estimated that approximately 80,000 individuals may
be considered as *at risk* cannabis users. Also, treatment demand for cannabis
problems has strongly increased in the past decade. In the public debate,
cannabis related problems have been linked with the recent doubling of
tetrahydrocannabinol (THC), the main psychoactive component, in Dutch domestic
grown marijuana.

Previous studies indicate that variables involved in initiation of cannabis use
differ from those involved in the development of cannabis dependence. Although
factors involved in initiation of use have been extensively studied, risk
factors involved in the transition to cannabis dependence and the course of
dependence, including treatment demand, are largely unravelled. This
multi-disciplinary study focuses on these issues and expects to generate useful
clues for prevention and treatment.

The primary objectives of the present study are: 1) to study factors involved
in the transition from risky non-dependent cannabis use to cannabis dependence,
2) to study the three-year natural course of cannabis dependence, including
factors predicting stability and recovery from cannabis dependence and 3) to
study factors related to treatment seeking in cannabis dependent users.
Secondary objectives are: 4) to compare characteristics of risky and dependent
cannabis users with control subjects from the general population and 5) to
validate self-reported measures of cannabis exposure.

With targeted sampling techniques, cohorts of 275 high risk cannabis users and
275 cannabis dependent subjects aged 18-30 years will be enrolled in a 3 years
prospective follow-up study. For descriptive analyses, they will be compared
with an age and sex matched group from a representative general population
study, NEMESIS 2. A randomly selected sub-sample of 20 at risk and 20 dependent
cannabis users (at baseline) from the cohort studies will be used for in-depth
analyses on dynamics of and the motivations underlying changes in cannabis
consumption patterns. A sub-sample of 100 participants will be studied to
validate self-reported cannabis consumption assessments, by using toxicological
information. To better understand *unmet need* and reasons for treatment, a
separate sample of 100 cannabis users new in treatment will be recruited from
addiction care institutions and interviewed in a cross sectional assessment.

The burden will mainly be in the duration of the interviews, and the fact that
in three years time several interviews will be conducted. To gain insight in
the natural course of heavy cannabis use and cannabis dependence, this follow
up design is necessary. We estimate that the burden resulting from the type of
questions (which are partly of general nature, such as demographic variables,
details of cannabis use, general functioning, partly assessing the presence of
psychiatric co-morbidity and (recent) life events) is acceptable. This
estimation is based on our previous experience with a questionnaire highly
comparable, which has been used for the Nemesis 1 study. This questionnaire did
not include in-depth questions on substance use, but to answer these questions
is not mentally distressing.

The risk associated with the sub-study on smoking behaviour, in which the
participant is asked to smoke a joint in a natural environment according to his
or her own habits and to hand over a couple of hairs, is not exceeding the
risks the participant takes in his or her daily life.