review paper prepared for DrugScope's submission to the Home Affairs
extensively from a technical paper by John Witton, National Addiction
Centre and Sarah Mars, London School of Hygiene and Tropical Medicine.
Headlines | Cannabis
& the Gateway Hypothesis | Gateway
Explanations | Licit Drugs as Gateways
| Conclusions | Case
Gateway theory has been and remains a key justification for much
of past and present government drugs policy.
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.
vast majority of cannabis users never progress to more harmful
Gateway Hypothesis takes as its starting point the user's environment
and behaviour rather than any properties of the drug itself.
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.
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
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.
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 (decriminalization 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.
contrast, Dutch policy has been to narrow the gateway by legal
reform and the gateway from cannabis to drugs like heroin and
crack does appeared to have been narrowed with an increase in
the age profile of heroin users.
Cannabis and the Gateway Hypothesis
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.
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
The Precursor of Gateway Theory: Stepping-Stone
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.
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.
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
The Gateway Hypothesis
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.
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.
The Gateway theory does not try to determine drug progression
it is simply about access to choices and proximity to drugs.
Evidence for Gateway Theory
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 claim(5) and while some studies
have shown variation in the pattern, one of the most recent and
most comprehensive studies in Christchurch New Zealand(6),
provided overwhelming evidence of stage theory.
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).
does Gateway exist?
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 emphasizing 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.
An alternative to the Gateway explanation:
Vulnerability and Risk
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).
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.
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.
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).
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.
Risk assessment Gateway
One gateway interpretation is that as 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(12)
. This means that they are more likely to move onto other 'more
harmful' drugs in the future.
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.
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
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 try (13). Here
the link between cannabis use and other drug use is explained by
its legal status and social context rather than its pharmacological
properties(14) . 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.
Analysis of Kandel et al's early findings showed that the relationship
between cannabis and other drug use was reduced once involvement
in the cannabis market and friends' drug use were taken into account(15).
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.
Drugs as Gateways
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.
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.
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.
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.
Gateway theory is often misunderstood. It is not about cannabis
leading to harder drugs, it is about common profiles, environment,
experience and access.
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;
Prohibition of all gateway drugs (logically including alcohol
and tobacco) should be enforced and therefore the gateways shut
through strict application of the law.
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(decriminalization or
similar) so that it is further differentiated from more harmful
drugs in perception, culture and supply.
Cannabis use in the UK is criminalized 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.
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.
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.
One possible result of current UK Cannabis policy is the growing
number of people progressing to using heroin and crack and particular
increases among young people(16). In 1998
for example, 80% of Drug Action Team networks and 81% of police
forces making returns indicated recent or new clusters (or in some
cases full scale outbreaks) of heroin use among young people in
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.
The Gateway theory was a key justification and reason for the
Dutch reform of domestic drug laws(18). 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
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).
1983 and O'Donnell and Clayton, 1982.
2Robins and Murphy, 1967.
and Horward 2000.
4Kandel and Faust, 1975; Ellickson et al. 1992.
6Fergusson and Horwood, 1997.
7Kandel and Davies, 1992.
8Fergusson and Horwood, 1997.
et al, 1994.
10Yamaguchi and Kandel 1984.
11Fergusson and Horwood 2000
13Goode, 1971 and Hall, 1994.
15Single and Kandel, 1978.
Misuse declared in 2000: Results from the British Crime Survey.
17Parker 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.
and Reuter, 1997.
19Netherlands Ministry of Justice, Fact Sheet: Dutch Drugs Policy,
(Utrecht: Trimbos Institute, Netherlands Institute of Mental Health
and Addiction, 1999).