Vista

Since 1997, drug use in the general population is monitored every four year in the Na- tional Prevalence Surveys on substance use. New data are available for 2009 (see also Online Standard Table 01). However, due to methodological changes, prevalence data from the 2009 survey are not comparable to those of previous years and consequently recent trends in drug use cannot be determined.

In 2009 5,769 respondents aged 15-64 years were successfully interviewed about sub- stance use as part of a broader general health survey (Van Rooij et al. 2011). The net response rate was 63%. The core of the questionnaire was administered by the Comput- erised Assisted Personal Interview (CAPI), but questions on drugs (and various other 'sensitive issues') were administered through Computer Assisted Self-Interviewing (CASI). In contrast, in previous surveys (1997, 2001 and 2005) data on drug use were (also) collected with the CAPI. A comparative analysis on data from 2006 in which both CAPI and CASI was used showed that CASI yields higher drug use prevalence rates than CAPI, especially in the younger age groups (Statistics Netherlands, per. communication K. Knoops). For example, last month prevalence of cannabis use among 15-24 year olds interviewed with the CAPI (n=490) was 6.5% against 12.0% for the CASI sample (n=660). Therefore, differences between 2005 and 2009 are more likely to reflect meth- odological differences rather than actual changes (mainly increases) in drug use.

Table 2.1.1 gives the lifetime and last year prevalence rates of drug use. The results show that in general lifetime and last year prevalence rates are higher in 2009 com- pared to 2005, but this is – as explained - most likely due to a mode difference.
The ranking of drugs in terms of prevalence remains the same, although the differ-

ence between last year use of cocaine and ecstasy is smaller.

GHB was included in the 2009 survey for the first time after signals of an increased use. Questions were included during a restricted data collection period (9 months in- stead of 12 months). Hence the number of respondents was slightly lower (N=4,599). In 2009 0.4% of the population had recently used GHB, which is similar to the last year prevalence of amphetamine use.

Incidence rate, defined as the percentage of first time users of all respondents in the past year, was highest for cannabis (1.2%), followed by ecstasy (0.5%), cocaine (0.4%), amphetamine (0.2%), LSD (0.1%) and heroin (0%). Incidence of cannabis use was highest among 15-24 year olds (5.7%). After age 24, the percentage of first time users sharply decreases (0.4% for age group 25-44 years and 0.2% for age group 45-64 years).

The reported prevalence rates on cannabis exclude users of medical cannabis (esti- mated lifetime prevalence 3.5%).

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Table 2.1.1: Prevalence of drug use (%) in the Dutch population of 15-64 years in 1997, 2001, 2005 and 2009*

Lifetime prevalence (%) Last year prevalence (%)

1997 2001 2005 ...** 2009 1997 2001 2005 ...** 2009 Cannabis 19.1 19.5 22.6b, c _{... 25.7 5.5 5.5 5.4 ... 7.0} Cocaine 2.6 2.1 3.4b, c _{... 5.2 0.7 0.7 0.6 ... 1.2} Ecstasy 2.3 3.2a _4.3b, c _{... 6.2 0.8 1.1 1.2}c _{... 1.4} Amphetamine 2.2 2.0 2.1 ... 3.1 0.4 0.4 0.3 ... 0.4 GHB*** - - - 1.3 - - - 0.4 LSD 1.5 1.2 1.4 ... 1.5 - 0.0 0.1 ... 0.1 Heroin 0.3 0.2 0.6b, c _{... 0.5 0.0 0.0 0.0 ... 0.1}

* N= 17,750 in 1997; N= 2,312 in 2001; N=4,516 in 2005, N=5,769 in 2009. ** Trend break due to a change in data collection method in 2009. *** Measured in a reduced sample (N=4,599) included in the survey from 1 April 2009-31 December 2009 instead of the whole year. a Significant change from 1997 to 2001. b Significant change from 2001 to 2005. c Significant change from 1997 to 2005. Differences between 2005 and 2009 were not tested for significance. Figures in italics = less than 50 cases. Source: National Prevalence Survey, IVO/Statistics Netherlands (Van Rooij et al., 2011).

Frequency of use

In 2009, last month prevalence of cannabis use was 4.7%; 30% of these last month users reported daily or almost daily use. This is some 1.3% of the total population aged 15 through 64 years, or 141.000 (almost) daily cannabis users in absolute numbers.

One quarter (25%) of the current users consumed cannabis a few times per week, 21% at least once per week and 24% less than once per week.

For other drugs the number of past month users is too small to allow a further break- down in frequency category.

Age and gender

The numbers of users are only sufficient for cannabis to make a breakdown by age and gender of recent users.

Cannabis use was highest in age group 25-44 years. In 2009 last year prevalence was twice as high in this age group compared to age group 25-44 (figure 2.1.1).
The prevalence of last year cannabis use was more than 2 times higher among men

Figure 2.1.1: Last year and last month prevalence (%) of cannabis use by age group in 2009

Source: IVO/Statistics Netherlands (Van Rooij et al., 2011).

Problem cannabis use and cannabis use disorders

From April 2009 until December 2009 the general population survey also included ques- tions on problems related to cannabis use. These questions were derived from the DSM IV criteria for cannabis dependence and may be considered as a proxy measure of prob- lem cannabis but they do not yield a clinical diagnosis of dependence. As these questions were introduced in the second quarter of 2009, the net sample was slightly lower (n=4,638 instead of 5,769), but prevalence rates of cannabis use were virtually the same (e.g. last year prevalence was 7.0% in the full sample and 7.1% in the reduced sample). Questions on problems related to cannabis use were only completed by respondents who had used cannabis at least five times in the past 12 months. Table 2.1.2 shows the per- centages of cannabis users fulfilling the criteria. Almost one quarter (23%) responded positive to three or more 'symptoms', which can be indicative of problem use.

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Table 2.1.2: Prevalence of symptoms of problem use of cannabis among recent users*

In the past 12 months, did you

Percentage with positive response

…continue use despite knowledge of having a persistent or recurrent physi- cal or psychological problem that is likely to have been caused or exacer- bated by the drug?

23% …spent a great deal of time in activities necessary to obtain the drug, using

it, or to recover from its effects? 13% …notice that you needed markedly increased amounts of the drug to achieve

intoxication or desired effect, or diminished effect with continued use of the same amount of the substance?

31% … often took the drug in larger amounts or over a longer period than was

intended? 19%

…have a desire or unsuccessful efforts to cut down or control use of the

drug? 46%

…give up, or reduce, important social, occupational, or recreational activities

(e.g. sports, work, family, friends) because of the continued drug use? 5% … feel bad (ill) when ceasing or reducing the drug or did you use another

substance to relieve or avoid these symptoms? 6%

* Recent users (n=188) who reported use of cannabis at least 5 times in the past 12 months. Source: Statistics Netherlands (personal communication K. Knoops).

NNIA. Between 2007 and 2009 a psychiatric epidemiological study was carried out on the prevalence and incidence of mental disorders, including DSM IV cannabis use disorders, in the general population from 18-64 years (NEMESIS-2, De Graaf et al. 2010). Baseline data were collected among 6,646 respondents (response rate of 65%). Face-to-face in- terviews were administered with the Composite International Diagnostic Interview (CIDI) 3.0.

An estimated 0.1% to 0.5% of the population aged between 18 and 64 met the crite- ria for a last year diagnosis of cannabis dependence (DSM 4th revised edition). An es- timated 0.2% to 0.6% of respondents met the criteria for a diagnosis of cannabis abuse. This means that about one in 9 last-year cannabis users has a cannabis use disorder (last year prevalence of cannabis use was 6.5%).

Cannabis-related disorders were more frequent among males than females (see table 2.1.3) and highest among 15-30 year olds (0.9% for cannabis dependence and 1.0% for cannabis abuse).

In population terms, there are an estimated 29,300 people with cannabis dependence and 40,200 with cannabis abuse. This population study did not survey juveniles aged under 18, people who were not sufficiently fluent in the Dutch language, and people who were homeless or were in a residential institution for a prolonged period. It is not known to what extent this may have influenced the results.

Table 2.1.3 Annual prevalence and numbers of people with a cannabis-related disorder (m/f). Between brackets: 95% Confidence Intervals. Survey period 2007- 2009 Disorder Males (%) Females (%) Total (%) Total (Number) Cannabis abuse 0.6 (0.2 – 1.0) 0.2 (0.0 – 0.4) 0.4 (0.2 – 0.6) 40,200 Cannabis dependence 0.4 (0.1 – 0.8) 0.1 (0.0 – 0.3) 0.3 (0.1 – 0.5) 29,300

Source: Nemesis 2007-2009 (De Graaf et al., 2010).