Cannabis and Young People

Reviewing the Evidence

Richard Jenkins

• Publisher: Jessica Kingsley Publishers
• Year: 2005
• ISBN:
  9781846424595
• Topic: Social Sciences
• Subtopic: Social Work
• Index: Social Sciences

Cannabis is at the centre of ongoing controversial and often confused debate. Opinions on its potential impact on health are sharply divided: some argue that it poses serious risks to mental health and that adolescent use may lead to psychotic illness in young adulthood, or that it acts as a gateway to hard drugs such as cocaine or opiates. Conversely, others point to alcohol or tobacco being far more harmful yet entirely legal.

Cannabis and Young People aims to shed light on the current debates by reviewing all the available evidence on a range of issues relating to the use of cannabis among children and adolescents and summarizing the main conclusions in clear, jargon-free language.
Areas covered include:

* Patterns of cannabis use

* Changes in usage

* Young people's views on cannabis

* The potential harmful effects, including mental health problems, educational attainment, antisocial behaviour

* The family and social factors that can initiate cannabis use

* The progression to regular use

* The effects of decriminalization

This book will be an essential read for anyone needing informed, authoritative information about cannabis and its effects.

1

Introduction
 

Cannabis has been the subject of considerable and often impassioned debate over the years. In 1967, The Times newspaper included a full-page advertisement signed by a variety of public figures, including the Beatles, that called for a review of the drug’s legal status (IDMU 2005). Opinion on the potential consequences of cannabis use is sharply divided, with some arguing that it poses serious risks to both physical and mental health, while others believe that any effects are modest by comparison with those of alcohol or tobacco (Wodak, Reinarman and Cohen 2002). A survey of over 1600 adults in the UK conducted by MORI in 1999 found that, although a majority of respondents wanted stronger drug laws, half of those questioned agreed that the law should be changed so that it was no longer illegal to use cannabis (Pearson and Shiner 2002).

Public discussion on the topic has intensified in the UK following the Home Office’s reclassification of cannabis as a Class C substance under the Misuse of Drugs Act in January 2004 (Home Office 2005). The production, supply and possession of cannabis remain illegal, although the maximum penalties have been reduced from five years’ to two years’ imprisonment. For young people under the age of 18, a first offence of possession results in an arrest and a formal warning or reprimand, with further offences leading to a final warning or charge. At the time of writing, however, the reclassification policy was being reviewed (BBC 2005a) following the publication of recent research demonstrating an association between cannabis use in adolescence and the reporting of psychotic symptoms in young adulthood (Fergusson, Horwood and Ridder 2005; Henquet et al. 2005).

In the light of these developments, the purpose of this book is to review the evidence on a range of issues relating to the use of cannabis among children and adolescents. Patterns of cannabis use are examined, drawing upon the latest prevalence figures from international and national surveys, together with findings from a number of large-scale cohort studies documenting changes in usage (e.g. from experimental to regular and higher frequency use) over the course of adolescence. Young people’s views about cannabis, including their assessment of its potential harmful effects in comparison with other substances and their reasons for using the drug, are also discussed. The findings from various longitudinal studies are summarised to highlight the individual, family and social factors that predict the initiation of cannabis use in adolescence, the progression to regular use and the likelihood of cessation in young adulthood. The review also includes the potential effects of cannabis use including mental health problems, other aspects of psychosocial functioning such as educational attainment and antisocial behaviour, and the use of other illicit drugs. Studies evaluating the effects of prevention programmes and treatment interventions, and the impact of changes in cannabis policy such as ‘decriminalisation’, are also considered.

Literature search strategy

Studies of cannabis use among children and adolescents, published from 1990 onwards, were identified from a search of the Cochrane Library and the Cinahl, Embase, Medline and Psycinfo bibliographic databases. The search was originally conducted in December 2004 and updated in March 2005. The titles and abstracts of the retrieved citations were assessed for their relevance to the research topics addressed by each of this book’s main chapters. Full text articles of the relevant citations were then obtained for critical appraisal, and their reference lists were checked for any additional relevant articles.

Wherever possible, existing systematic reviews, meta-analyses or other detailed literature reviews formed the basis of the evidence for each of the research topics. Individual studies were then considered according to a ‘hierarchy of evidence’ reflecting the robustness of their methodological designs (Khan et al. 2003). For example, the review of evidence examining the association between cannabis use and psychosocial functioning concentrated on longitudinal cohort studies that featured prospective measures of cannabis use and statistical analyses controlling for the effects of confounding variables. Prevention programmes and treatment interventions were evaluated primarily in terms of randomised controlled trials or RCTs. These involve the random allocation of participants to an intervention or control group, with follow-up assessments to examine differences in the outcomes between the groups. The process of randomisation is designed to balance the groups for known as well as unknown variables that may have an impact on the final outcomes.

Cannabis terminology

The term ‘cannabis’ refers to several products that may be obtained from the cannabis or hemp plant (Drugscope 2005). Cannabis resin (hashish, hash) is the secretion from the flowering tops of the plant, which is then pressed into brown or black blocks. Herbal cannabis (marijuana, grass, ganga) is the dried flower-bearing stems and top shoots of the plant, and sometimes also the leaves and parts of the stem. Cannabis oil is a thick, brown or black liquid that is made by percolating a solvent through the resin. The psychoactive effects of cannabis are caused by chemical substances known as cannabinoids, the most potent type being tetrahydrocannabinol (THC) (Ashton 2001).

2

Patterns
of Cannabis Use

Prevalence of use

International surveys

Two of the main sources of international data on the prevalence of cannabis use among children and adolescents are the Health Behaviour in School-aged Children study (HBSC) and the European School Survey Project on Alcohol and Other Drugs (ESPAD). To date, there have been six HBSC surveys, collecting data on a range of health topics from school pupils aged 11, 13 and 15 years. The latest available findings are from the 2001/02 survey, which involved 35 countries and other territories in Europe and North America (Currie et al. 2004). Questions on cannabis use were included for the first time, although for the 15-year-old age group only, on the grounds that use of the drug is infrequent among children and early adolescents. The sample size of respondents in this age group ranged from 240 in Greenland to 2614 in France, with 15 countries achieving the target of 1500 pupils. The 2001/02 survey showed that the proportion of 15-year-olds across all the HBSC countries who had used cannabis at least once during their lives was 25.8% in the case of males and 18.9% for females. Of these respondents, 7.3% were classified as ‘experimental’ users (one to two times), 7.9% reported ‘recreational’ use (three to 39 times) and 2.8% were ‘heavy’ users (40 or more times). Heavy users comprised between 5 and 10% of the samples in Canada, England, Scotland, Spain, Switzerland and the US. In all countries, heavy use was more common among boys than girls. Use of the drug during the previous year ranged from a low of 3% in the former Yugoslav Republic of Macedonia to a high of 40% in Canada. Over 30% of pupils in England, Greenland, Scotland, Spain, Switzerland and the US reported past-year use of the drug. Overall, cannabis use across the HBSC countries was more common among boys (21.7%) than girls (16%).

The ESPAD documents the level of substance use across Europe among school pupils who are, or will become, 16 years old during the year of data collection. The first survey, involving 26 countries, was completed in 1995, the second in 1999 and the latest in 2003, featuring over 100,000 pupils from 35 countries (ESPAD 2005). The number of participants in each country ranged from 555 in Greenland to almost 6000 in Poland, although in most cases the sample size was close to or above the recommended target of 2400. In 2003, the Czech Republic had the highest ‘lifetime’ prevalence rate of marijuana or hashish use, with 44% reporting use of the drug at least once during their lives. High rates were also reported in Switzerland (40%), Ireland (39%), the Isle of Man (39%), France (38%) and the UK (38%). The lowest levels (under 5%) were for Cyprus, Romania and Turkey. The country with the highest proportion of pupils using the drug during the last month was France (22%), followed by the Isle of Man (21%), Switzerland (20%) and the UK (20%). The lowest levels (under 5%) were reported in Cyprus, the Faroe Islands, Finland, Greece, Iceland, Latvia, Malta, Norway, Romania, Sweden and Turkey. In most ESPAD countries, cannabis use was more common among boys than girls.

Surveys of use in the UK

A series of surveys have been conducted on behalf of the Department of Health since 1982 to examine the prevalence of health-related behaviours among 11- to 15-year-old school pupils in England. Questions on illegal drug use were first included in 1998. The latest available data on cannabis use are from the 2004 survey, involving a sample of nearly 10,000 pupils from 313 schools across the country (Department of Health 2005). In 2004, 11% of pupils reported using cannabis at least once during the previous year, compared with 13% in the 2001, 2002 and 2003 surveys. Prevalence was slightly higher among boys (12%) than girls (10%) and increased with age, from 1% of 11-year-olds to 7% of 13-year-olds and 26% of 15-year-olds.

The 2004 Scottish Schools Adolescent Lifestyle and Substance Use Survey (SALSUS) details the prevalence of smoking, drinking and substance use among secondary 2 and 4 grade pupils (i.e. mainly 13- and 15-year-olds, respectively) in Scotland (Corbett et al. 2005). A total of 340 classes in 194 schools participated, with 7062 pupils completing questionnaires. Cannabis use in the year prior to the survey was reported by 10% of 13-year-olds and 28% of 15-year-olds. For use in the previous month, the figures were 7% of 13-year-old boys and 5% of 13-year-old girls, rising to 20% of 15-year-old boys and 18% of 15-year-old girls.

The HBSC provides the latest data on cannabis use among adolescents across Wales, with the 2001/02 survey involving approximately 1500 15-year-old school pupils (Currie et al. 2004). The proportion of the sample reporting the use of cannabis in the last year was 26% for boys and 24% for girls. Among the HBSC countries, Wales was ranked tenth highest, with England third and Scotland seventh. Three per cent of the Welsh sample who reported cannabis use at least once during their lives were classified as heavy users (40 or more times), compared with 6% in Scotland and 7% in England.

The use of cannabis among school children in Northern Ireland was documented in the 2003 Young Person’s Behaviour and Attitudes Survey, which collected data on a range of health and social issues from a sample of 7223 students, aged 11 to 16, in 74 schools (Central Survey Unit 2005). Just over 13% reported using cannabis at some point during the previous year, with 8.5% using the drug in the last month and 4.5% in the last week.

One important limitation of these school-based surveys is the lack of detailed figures on substance use among different ethnic groups. To address this issue, Rodham et al. (2005) examined ethnic differences in the prevalence of a number of health-related behaviours, including drug taking, among a sample of 15- to 16-year-old pupils from schools in Oxfordshire, Northamptonshire and Birmingham. Sixty-four schools, varying in terms of their size, type (state, grammar or independent), gender (single sex or co-educational), educational attainment, socio-economic deprivation and ethnic composition, were asked to participate and 41 agreed to do so. A total of 6020 pupils completed questionnaires on substance use and recorded their ethnic status from a list of four categories (‘White’, ‘Asian’, ‘Black’ or ‘Other’). The ethnic composition of the sample was similar to that for England as a whole, except for a greater proportion of pupils describing themselves as being of Asian origin. Among male pupils, the reporting of cannabis use in the past year was more common among those describing their ethnic status as ‘Black’ (49.3%) or ‘Other’ (44.3%) than White (33.5%). Asian pupils of both genders were the least likely of the four ethnic categories to report past-year cannabis use (21.5% of males and 5.5% of females).

An additional criticism of school-based surveys is that they are likely to underestimate the true extent of substance use, since drug-taking is typically higher among adolescents who truant or are excluded from school (Lloyd 1998; Miller and Plant 1999). Cannabis use among these two groups was examined by the Youth Lifesyles Survey 1998/99, involving a sample of 4848 young people, aged 12 to 30, in England and Wales (Goulden and Sondhi 2001). Figures for school truants (truanting from school for a whole day in the past year without permission) and excluded pupils (missing school at least one day per term or expelled/suspended at some point during their school career) were recorded for the 12 to 16 age group. The proportions reporting cannabis use during the past year were 42% in the case of truants and 34% of excluded pupils, compared with 8% of pupils attending school on a regular basis. With regard to gender differences, cannabis use during the last year was significantly higher among female truants (52%) compared with males (32%). Excluded female pupils also reported significantly higher cannabis use (52%) than males (29%).

The main sources of information about the prevalence of illegal drug use among older adolescents (age 16 and over) in the UK are from household surveys such as the British Crime Survey (BCS). The BCS samples a representative cross-section of 16- to 59-year-olds living in private households in England and Wales. In addition to asking respondents about their experiences of crime, the survey has included questions on the use of illicit drugs since 1996. The 2002/03 survey found that just under a quarter (24.6%) of 16- to 19-year-olds had used cannabis in the past year and 15.3% had used the drug in the previous month (Condon and Smith 2003). In the 2003 Scottish Crime Survey (McVie, Campbell and Lebov 2004), 21% of 16- to 19-year-olds in Scotland reported past-year cannabis use, with a higher rate among males (25%) than females (15.7%). The Drug Prevalence Survey, covering Northern Ireland and the Irish Republic, was conducted for the first time in 2002/03, involving a representative sample of 15- to 64-year-olds who were normally resident in private households (NACD and DAIRU 2003). The final achieved sample for Northern Ireland was 3517, representing a response rate of 63%. Among the 15- to 24-year-old age group, 12% of respondents reported use of cannabis in the past year and 8% stated that they had used the drug in the last month.

Household surveys are a useful indicator of how many adolescents have tried cannabis but they often lack information on the frequency and other aspects of use. A questionnaire study by McCambridge and Strang (2004a) provided a more detailed picture of cannabis use among a sample of 200 young people attending 10 further education colleges in inner London. The participants were aged 16 to 20 and all were currently involved in illegal drug use on more than an occasional basis, defined as a minimum of weekly cannabis use and/or current stimulant drug use within the previous three months. Ninety-six participants (48% of the sample) stated that they used cannabis either every day or nearly every day, with an average of 26.6 episodes of use per week. Sixty-two participants (31%) reported weekly (but not daily) use of the drug, with an average of 6.6 episodes of use per week. The most common form of cannabis used was ‘grass’ (49%), followed by ‘skunk’ (36%). Almost half of the sample (49%) stated that all, or nearly all, of their friends used cannabis, and 45% reported that they never, or almost never, used cannabis alone.

Like school-based studies, household surveys of substance use are also prone to underestimating the level of substance use in the general population, as they do not sample groups such as the homeless or young offenders. The prevalence of cannabis use among the young homeless in four areas of England and Wales (Birmingham, Brighton and Hove, Canterbury and Cardiff) was documented in a report from the UK Home Office Drug Research Programme (Wincup, Buckland and Bayliss 2003). Data were collected from a total of 160 young people, aged 25 and under, recruited through homelessness agencies. Cannabis use in the past year was reported by 80% of the 35 respondents aged 16 to 17. In another Home Office report, Hammersley, Marsland and Reid (2003) examined substance use among a sample of 293 young people aged 12 to 18 from 11 youth offending teams across England and Wales. Eighty six per cent of the sample reported using cannabis at least once during their lives, with 71% having used it in the last four weeks. Of those who had used cannabis at some point during the previous year, 71% were classified as ‘heavier’ users (25 to 365 times).

Changes in use over time

A number of large-scale, longitudinal cohort studies have provided information on changes in the patterns of cannabis use during the course of adolescence, such as the proportion of individuals who go on to become regular users or develop dependence on the drug.

Christchurch Health and Development Study (CHDS)

The CHDS comprises a cohort of 1265 children born in the Christchurch urban region of New Zealand in mid-1977 (Fergusson and Horwood 2001). The cohort has been assessed at birth, four months, one year, at annual intervals until age 16 years, and again at 18, 21 and 25 years.

Fergusson and Horwood (2000a) describe the development of cannabis use in the Christchurch cohort up to the age of 21 years. Cohort...

Table of contents

• Cover Page
• Other Books
• Title Page
• Copyright
• Contents
• 1. Introduction
• 2. Patterns of Cannabis Use
• 3. Young People’s Views about Cannabis
• 4. Predictors of Cannabis Use
• 5. Cannabis and Psychosocial Functioning
• 6. Cannabis and the Use of Other Illicit Drugs
• 7. Prevention and Treatment
• 8. Cannabis Policy
• 9. Concluding Comments
• Resources
• References
• Subject Index
• Author Index
• About FOCUS