Select Committee on Home Affairs Memoranda

Annex B


  Drawn extensively from a technical paper by John Witton, National Addiction Centre and Sarah Mars, London School of Hygiene and Tropical Medicine.


    —  The Gateway theory has been and remains a key justification for much of past and present government drugs policy.

    —  "Stepping-Stone" theory (often confused for gateway theory) which posits that cannabis use "causes", or leads inexorably to the use of more harmful drugs like crack or heroin is false.

    —  The vast majority of cannabis users never progress to more harmful drugs.

    —  The Gateway Hypothesis takes as its starting point the user's environment and behaviour rather than any properties of the drug itself.

    —  There is good scientific evidence for the existence of a gateway phenomenon in various longitudinal studies, which is not sufficiently explained by mere risk or vulnerability factors.

    —  There are two main explanations for the way cannabis acts as a gateway;

  1.  Risk Assessment—cannabis users do not find cannabis bringing the harms that have been attributed to it, so their expectations of risk for other drugs are lowered, making them more likely to try them.

  2.  Legal/Social—cannabis use brings cannabis users into contact with people (who otherwise they may never have met) using or selling more harmful drugs, which they may then try.

    —  If the aim of policy makers is to reduce the number of people moving through the cannabis gateway onto more harmful drugs, the gateways can be closed or narrowed in one of two ways;

  1.  Strict prohibition with accompanying strict sanctions and a zero-tolerance enforcement policy.

  2.  More accurate harm information and a change in the legal status of cannabis (decriminalisation or similar) so that it is further differentiated from more harmful drugs in perception, culture and supply.

    —  Current UK drug policy is the worst possible scenario where the gateway from cannabis to heroin or crack is left wide open and we have growing heroin and crack using population.

    —  In contrast, Dutch policy has been to narrow the gateway by legal reform and the gateway from cannabis to drugs like heroin and crack does appear to have been narrowed with an increase in the age profile of heroin users.


  1.  The hypothesis that cannabis use leads to the use of other more harmful drugs has been, and remains, a key justification of past and present drug policy. Gateway theory and its precursors have coloured public perception of the risks of cannabis use, underpinned the emphasis on cannabis in prevention interventions and supplied a rationale for its continuing prohibition.

  2.  This paper sets out the strengths and failings of the hypothesis, dismisses the more dogmatic variations and sets out the differing options open to policy makers interpreting the existence of such a gateway.


  3.  Gateway theory has evolved from the "Stepping-Stone" theory, for which it is often still confused. The Stepping-Stone theory argues that cannabis use leads inexorably to the use of harder drugs culminating with heroin or crack. This is based on predominately physiological explanations; that cannabis use unleashes chemicals in the brain that desire new drugs or that cannabis users, after experiencing and getting used to the mild high of cannabis, begin to crave a more intense high and thus move on to other drugs.

  4.  The Stepping-Stone theory has proved unsustainable and lacking any real evidence base.1 The "evidence": that most heroin users started with cannabis,2 is hardly surprising and demonstrably fails to account for the overwhelmingly vast majority of cannabis users who do not progress to drugs like crack and heroin.

  5.  The Stepping-Stone theory (often confused among the general public for the Gateway theory as previously mentioned) has been dismissed by scientific inquiry. The notion that cannabis use "causes" further harmful drug use has been, and should be, comprehensively rejected.


  6.  The Gateway Hypothesis takes as its starting point the user's environment and behaviour rather than the drug itself. The theory posits that drug using careers follow a generally predictable progression in which the individual moves from using legitimate drugs including alcohol and tobacco to various forms of illicit drug use.3 This is different from Stepping-Stone theory in that there is no inexorable direction to the drug users choices.

  7.  Gateway theory is a metaphor where the individual has access to new gates after entering the first gate/field but may or may not choose to open those new gates. Individuals may go back to where they started, they may stay in the first field, or they may decide to open further gates and move onto use other drugs.

  8.  The Gateway theory does not try to determine drug progression it is simply about access to choices and proximity to drugs.


  9.  The Gateway hypothesis is underpinned by the stage theory of substance use.4 The prominent prediction of this theory is that drug use follows a developmental sequence where those using illicit drugs will invariably have used alcohol or tobacco but not all those using illicit drugs such as cannabis will move on to using more harmful illicit drugs such as heroin or cocaine. Substantial research has provided a solid evidence base for this claim5 and while some studies have shown variation in the pattern, one of the most recent and most comprehensive studies in Christchurch New Zealand6 provided overwhelming evidence of stage theory.

  10.  Research has also shown that regular users of cannabis are much more likely to progress to more harmful drugs than occasional users,7 as are those who use cannabis from an earlier age.8


  11.  It appears therefore that the effects of a Gateway theory do exist in empirical evidence. The explanations for it are numerous and varied. It is worth emphasising once again that the Gateway thesis is not dictating or predicting what will happen to people trying cannabis, it is an analytical tool for understanding individual's drug use. Gateway theory is based on the users behaviour and environment and not on any qualities or effects of the drug itself.


  12.  The evidence for Gateway theory can also be seen as evidence for correlations other than the Gateway explanation. The explanation based on patterns of vulnerability and risk posits that cannabis takes its place among a range of anti-social/non-conformist behaviour patterns that make the individual more likely to become more heavily involved in cannabis and other illicit drugs. Research has shown that cannabis users are more likely to have a history of anti-social behaviour and non-conformity, to perform more poorly at school and to use drugs to deal with negative personal feelings.9

  13.  The link between cannabis and other drug use, according to this explanation, is thus a reflection that there are a number of risk factors and life pathways that predispose young people to use cannabis and that they overlap with the life pathways that predispose young people to use other illicit drugs.

  14.  Cannabis happens to be the most easily available to those predisposed to use illicit drugs so it is used before other drugs. Once these common risk factors are taken into account, the use of other drugs by cannabis users is seen as a common behavioural symptom and not something caused by cannabis use.

  15.  This explanation has been extensively tested and found to be generally true but with a correlation over and above it.10 In experiments where they have sought to control these vulnerability factors the correlation between cannabis and other drug use remains.11

  16.  One can therefore conclude that although vulnerability is one explanation for the Gateway theory occurring empirically it is not on its own a sufficient explanation.


1.  Risk assessment Gateway

  17.  One gateway interpretation is that as cannabis users do not fine cannabis bringing the harms that have been attributed to it, so their expectations of risk for other drugs are lowered.12 This means that they are more likely to move onto other "more harmful" drugs in the future.

  18.  This finding has significant policy implications. This Gateway is not a necessary one but the result of current drug information and emphasis. A policy which distanced cannabis from other more harmful drugs, either though more accurate harm information or a change in cannabis' legal status, would make individuals more likely to accept the harm information around drugs like heroin and therefore make cannabis users less likely to move onto more harmful drugs.

  19.  It is therefore possible to conclude that this gateway can be pulled shut (or at least partially shut) by governmental action and legal reform.

2.  Sociological Gateways

  20.  A further suggested reason for the apparent gateway occurrence is that cannabis use brings cannabis users into contact with people (who otherwise they may never have met) using or selling more harmful drugs, which they may then try13. Here the link between cannabis use and other drug use is explained by its legal status and social context rather than its pharmacological properties14. Evidence suggests that cannabis users have a high level of contact with cannabis using peers and drug sellers where illicit drug use is encouraged and approved of.

  21.  Analysis of Kandel's early findings showed that the relationship between cannabis and other drug use disappeared once involvement in the cannabis market was taken into account.15

  22.  In a similar way to the risk assessment explanation, this gateway can be narrowed by further differentiation between cannabis and other drugs. By differentiating further in law between cannabis and more harmful drugs, policy makers can reduce the social relationship between them and to a large extent remove supply from individuals likely to be supplying more harmful drugs as well as cannabis. In the same way as the risk assessment gateway, this sociological gateway can be pulled shut (or at least partially shut) by governmental action and legal reform.


  23.  The Gateway hypothesis is not restricted to cannabis or illicit drugs; indeed alcohol and tobacco are consistently identified as the first "gate" through which almost all illicit drug users pass.

  24.  This well illustrates the nature of the gateway theory: regularly smoking tobacco and/or drinking alcohol may bring individuals into contact with a higher number of people who use other drugs (like cannabis) and it may reduce peoples harm analysis of other drugs. Alcohol and tobacco is not however a "cause" of illicit drug use; people who drink and smoke progress to crack or heroin only very rarely, in the same way, people who use cannabis progress to crack or heroin only very rarely. A survey of heroin users would find almost all of them had used not just cannabis, but tobacco and alcohol as well, but this does not mean any of them is a cause.


  25.  The weight of empirical evidence would suggest that a link between cannabis and more harmful drugs like heroin and crack does exist. The reason for this is not as the stepping stone theory suggested, it is not a cause or a chemical process that cannabis started, it is rather that:

    —  Some cannabis users have common personality profiles or environmental conditions with the users of more harmful drugs.

    —  Once drugs, be they cannabis, alcohol or tobacco are used, if the harm ascribed to them is overrated or false, individuals using cannabis will dismiss harm information and are less likely to be concerned about moving to more "harmful" drugs.

    —  Cannabis use puts individuals in social situations and supply transactions where they are more likely to experience people using, accepting and supplying more harmful drugs than others in the population.

  26.  Gateway theory is often misunderstood. It is not about cannabis leading to harder drugs, it is about common profiles, environment, experience and access.

  27.  Policy makers who wish to reduce the number of people moving through the gateways to more harmful drugs have the opportunity to interpret the existence of Gateway theory in one of two ways:

    (a)  Prohibition of all gateway drugs (logically including alcohol and tobacco) should be enforced and therefore the gateways shut through strict application of the law.

    (b)  If it is not possible (as current levels of cannabis use would suggest) or desirable to adopt a zero tolerance policy to cannabis (if not alcohol and tobacco) through prohibition and strict legal sanctions, policy makers should narrow the Gateways as much as possible. This can only be done by producing more accurate harm information and by changing the legal status of cannabis (decriminalisation or similar) so that it is further differentiated from more harmful drugs in perception, culture and supply.



  28.  Cannabis use in the UK is criminalised with strict sanctions available if not widely used. Despite this prohibition, cannabis use has grown and it has become politically and practically impossible to enforce a zero tolerance policy to cannabis use.

  29.  Cannabis supply remains in the hands of illegal suppliers many of whom also supply more harmful drugs also. Cannabis possession remains criminalised and closely associated in law and society with more harmful drugs.

  30.  This scenario, the status quo, is the worst possible combination. Cannabis use is wide spread and its legal status differentiates only marginally between it and other drugs with resulting social association. The cannabis gateway in the UK is thus wide open.

  31.  One possible result of current UK Cannabis policy is the growing number of people progressing to use heroin and crack and particular increases among young people.16 In 1998 for example, 80 per cent of Drug Action Team networks and 81 per cent of police forces making returns indicated recent or new clusters (or in some cases full scale outbreaks) of heroin use among young people in their area.17

  32.  If policy makers wish to reduce the number of people using cannabis as a gateway to more harmful drugs, policy makers need to close or narrow the gateway by deciding which option set out above they wish to follow.


  33.  The Gateway theory was a key justification and reason for the Dutch reform of domestic drug laws18. In the Netherlands no sanctions are now applied to the use of cannabis and the Government allows certain "cafes" to supply cannabis in small amounts. The effect of this has been to differentiate between cannabis and other illicit drugs and to remove the final supply from individuals who may also have been in possession of other more harmful drugs.

  34.  Empirical evidence since the reform would suggest the legal changes have reduced the extent to which cannabis acts as a gateway to more harmful drugs. The number of addicts in the Netherlands in stable, drug related deaths are lower and the age profile of Heroin users is rising, directly opposite to the position in the UK.19

September 2001


    1 Baumrind, 1983 and O'Donnell and Clayton, 1982.

    2 Robins and Murphy, 1967.

    3 Fergusson and Horward 2000.

    4 Kandel and Faust, 1975; Ellickson et al. 1992.

    5 Kandel, 1975, 1978, 1984

    6 Fergusson and Horwood, 1997.

    7 Kandel and Davies, 1992.

    8 Fergusson and Horwood, 1997.

    9 Hall et al. 1994.

  10 Yamaguchi and Kandel, 1984.

  11 Fergusson and Horwood, 2000.

  12 MacCoun, 1998.

  13 Goode, 1971 and Hall, 1994.

  14 Lenton, 2000.

  15 Single and Kandel, 1978.

  16 Drug Misuse declared in 2000: Results from the British Crime Survey.

  17 Parker H, Bury C, Egginton R. New Heroin Outbreaks Amongst Young People in England and Wales. Crime Detection and Prevention Series Paper 92. London: Home Office 1998.

  18 MacCoun and Reuter, 1997.

  19 Netherlands Ministry of Justice, Fact Sheet: Dutch Drugs Policy, (Utrecht: Trimbos Institute, Netherlands Institute of Mental Health and Addiction, 1999).

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