Elsevier

The Lancet

Volume 374, Issue 9698, 17–23 October 2009, Pages 1383-1391
The Lancet

Review
Adverse health effects of non-medical cannabis use

https://doi.org/10.1016/S0140-6736(09)61037-0Get rights and content

Summary

For over two decades, cannabis, commonly known as marijuana, has been the most widely used illicit drug by young people in high-income countries, and has recently become popular on a global scale. Epidemiological research during the past 10 years suggests that regular use of cannabis during adolescence and into adulthood can have adverse effects. Epidemiological, clinical, and laboratory studies have established an association between cannabis use and adverse outcomes. We focus on adverse health effects of greatest potential public health interest—that is, those that are most likely to occur and to affect a large number of cannabis users. The most probable adverse effects include a dependence syndrome, increased risk of motor vehicle crashes, impaired respiratory function, cardiovascular disease, and adverse effects of regular use on adolescent psychosocial development and mental health.

Introduction

Psychoactive preparations of Cannabis sativa have been used for over 4000 years for medical and religious purposes.1 Over the past 50 years, they have been increasingly adopted by adolescents and young adults for recreational use—in social settings to increase sociability and produce euphoric and intoxicating effects. Since cannabis use was first reported over 40 years ago by US college students, its recreational or non-medical use has spread globally, first to high-income countries, and recently to low-income and middle-income countries2, 3 (Figure 1, Figure 2).

Uncertainties exist about the number of people who use cannabis because of lack of timely, good-quality data in most countries. The UN Office on Drugs and Crime has estimated that in 2006 cannabis was used by 166 million adults (3·9% of the global population aged 15–64 years).4 Use was the highest in the USA, Australia, and New Zealand, followed by Europe. These countries reported higher rates of cannabis use than did the Middle East and Asia.4 Some African countries are also thought to have high rates of cannabis use.4 Because of their large populations, 31%, 25%, and 24% of the world's cannabis users are estimated to be from Asia, Africa, and the Americas, respectively, compared with 18% in Europe and 2% in Oceania4 (figure 1).

Section snippets

Pattern of cannabis use

In the USA, rates of cannabis use in young adults peaked in 1979, which was followed by a long decline until the early 1990s, when use increased again, before levelling off towards the end of the decade.5 A similar rise in its use in the early 1990s, followed by decline or stabilisation in recent years, has been reported in Australia and western Europe.5

Research in the USA has indicated that about 10% of those who ever use cannabis become daily users, and 20% to 30% become weekly users.5

Cannabis

The effects of cannabis depend on the dose received, the mode of administration, the user's previous experience with this drug, and the set and setting—ie, the user's expectations, attitudes towards the effects of cannabis, the mood state, and the social setting in which it is used.5 The main reason why most young people use cannabis is to experience a so-called high: mild euphoria, relaxation, and perceptual alterations, including time distortion and intensification of ordinary experiences

Health effects of cannabis

We looked for evidence: that an association exists between cannabis use and outcomes in case–control and prospective studies; that reverse causation was an implausible explanation of the association (evidence from prospective studies that cannabis use preceded the outcome); from prospective studies that controlled for potential confounding variables (such as other drug use and characteristics on which cannabis users differed from non-users); and that a causal association was biologically

Other illicit drug use

In the USA, Australia, and New Zealand, regular cannabis users were most likely to later use heroin and cocaine, and the earlier the age at which a young person uses cannabis, the more likely they are to use heroin and cocaine.71 Three explanations have been given for these patterns of drug involvement: cannabis users have more opportunities to use other illicit drugs because cannabis is supplied by the same black market; those who are early cannabis users are more likely to use other illicit

Cannabis and mental health

Cannabis use has been associated with increased risk of psychiatric disorders. A 15-year follow-up of 50 465 Swedish male conscripts reported that those who had tried cannabis by age 18 years were 2·4 times more likely to be diagnosed with schizophrenia than those who had not.81 Risk increased with the frequency of cannabis use and remained significant after statistical adjustment for a few confounding variables. Those who had used cannabis ten or more times by 18 years of age were 2·3 times

Increased THC content in cannabis products

Concerns have been expressed over the past 20 years about putative increases in the potency of cannabis products,5 which recent studies suggest may have occurred during the late 1990s.14 It is unclear whether increased THC content has been accompanied by any changes in CBD content. Any health effects of increased potency depend on whether users are able and willing to titrate their dose of THC, and might also vary with the experience of users. A high THC content can increase anxiety,

Conclusions

Acute adverse effects of cannabis use include anxiety and panic in naive users, and a probable increased risk of accidents if users drive while intoxicated (panel 1). Use during pregnancy could reduce birthweight, but does not seem to cause birth defects. Whether cannabis contributes to behavioural disorders in the offspring of women who smoked cannabis during pregnancy is uncertain.

Chronic cannabis use can produce a dependence syndrome in as many as one in ten users. Regular users have a

Search strategy and selection criteria

We searched PubMed and Thompson Reuters Web of Science citation indexes for articles published in the past 10 years on adverse health effects of cannabis, with the search terms “cannabis”, “marijuana abuse”, “marijuana smoking”, “epidemiologic studies”, “adverse effects”, “substance related disorders”, “lung diseases”, “respiration disorders”, “cardiovascular diseases”, “coronary disease”, “traffic accidents”, “automobile driving”, “mental disorders”, and “adolescent”. Most selected

References (96)

  • J Macleod et al.

    Psychological and social sequelae of cannabis and other illicit drug use by young people: a systematic review of longitudinal, general population studies

    Lancet

    (2004)
  • M Hashibe et al.

    Epidemiologic review of marijuana use and cancer risk

    Alcohol

    (2005)
  • J Berthiller et al.

    Cannabis smoking and risk of lung cancer in men: a pooled analysis of three studies in Maghreb

    J Thorac Oncol

    (2008)
  • KJ Mukamal et al.

    An exploratory prospective study of marijuana use and mortality following acute myocardial infarction

    Am Heart J

    (2008)
  • RI Block et al.

    Effects of frequent marijuana use on memory-related regional cerebral blood flow

    Pharmacol Biochem Behav

    (2002)
  • DM Fergusson et al.

    The developmental antecedents of illicit drug use: evidence from a 25-year longitudinal study

    Drug Alcohol Depend

    (2008)
  • J Manzanares et al.

    Pharmacological and biochemical interactions between opioids and cannabinoids

    Trends Pharmacol Sci

    (1999)
  • S Andréasson et al.

    Cannabis and schizophrenia: a longitudinal study of Swedish conscripts

    Lancet

    (1987)
  • TH Moore et al.

    Cannabis use and risk of psychotic or affective mental health outcomes: a systematic review

    Lancet

    (2007)
  • L Degenhardt et al.

    Testing hypotheses about the relationship between cannabis use and psychosis

    Drug Alcohol Depend

    (2003)
  • V Ajdacic-Gross et al.

    Changing incidence of psychotic disorders among the young in Zurich

    Schizophr Res

    (2007)
  • EL Abel

    Marihuana: the first twelve thousand years

    (1980)
  • WD Hall et al.

    Prevalence and correlates of cannabis use in developed and developing countries

    Curr Opin Psychiatry

    (2007)
  • World drug report 2006. Volume 1: analysis

    (2006)
  • World drug report 2008

    (2007)
  • WD Hall et al.

    Cannabis use and dependence: public health and public policy

    (2003)
  • JG Bachman et al.

    Smoking, drinking, and drug use in young adulthood: the impacts of new freedoms and new responsibilities

    (1997)
  • Cannabis: a health perspective and research agenda

    (1997)
  • B Green et al.

    Being stoned: a review of self-reported cannabis effects

    Drug Alcohol Rev

    (2003)
  • L Iversen

    The science of marijuana

    (2008)
  • SR Wachtel et al.

    Comparison of the subjective effects of Delta(9)-tetrahydrocannabinol and marijuana in humans

    Psychopharmacology (Berl)

    (2002)
  • RM Murray et al.

    Cannabis, the mind and society: the hash realities

    Nat Rev Neurosci

    (2007)
  • L Chang et al.

    Functional imaging studies in cannabis users

    Neuroscientist

    (2007)
  • MA ElSohly

    Quarterly report: December 16, 2007 thru March 15, 2008

    (2008)
  • J McLaren et al.

    Cannabis potency and contamination: a review of the literature

    Addiction

    (2008)
  • RS Gable

    Comparison of acute lethal toxicity of commonly abused psychoactive substances

    Addiction

    (2004)
  • N Solowij

    Cannabis and cognitive functioning

    (1998)
  • A Smiley

    Marijuana: on road and driving simulator studies

  • Robbe HWJ. Influence of marijuana on driving. PhD thesis, Maastricht: Institute for Human Psychopharmacology,...
  • B Laumon et al.

    Cannabis intoxication and fatal road crashes in France: population based case-control study

    BMJ

    (2005)
  • F Grotenhermen et al.

    Developing limits for driving under cannabis

    Addiction

    (2007)
  • E Bloch

    Effects of marijuana and cannabinoids on reproduction, endocrine function, development, and chromosomes

  • MB Forrester et al.

    Risk of selected birth defects with prenatal illicit drug use, Hawaii, 1986–2002

    J Toxicol Environ Health A

    (2007)
  • K Tennes et al.

    Marihuana: prenatal and postnatal exposure in the human

  • B Zuckerman et al.

    Effects of maternal marijuana and cocaine use on fetal growth

    N Engl J Med

    (1989)
  • D English et al.

    Maternal cannabis use and birth weight: a meta-analysis

    Addiction

    (1997)
  • JC Anthony

    The epidemiology of cannabis dependence

  • JC Anthony et al.

    Comparative epidemiology of dependence on tobacco, alcohol, controlled substances and inhalants: basic findings from the National Comorbidity Survey

    Exp Clin Psychopharmacol

    (1994)
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