CANNABIS AND THE GATEWAY HYPOTHESIS
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
(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
There are two main explanations for
the way cannabis acts as a gateway;
1. Risk Assessmentcannabis 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/Socialcannabis 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
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
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
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
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
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
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
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"
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
1 Baumrind, 1983 and O'Donnell and Clayton,
2 Robins and Murphy, 1967.
3 Fergusson and Horward 2000.
4 Kandel and Faust, 1975; Ellickson et
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
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).