Advisory Council on the Misuse of Drugs
The classification of cannabis under the Misuse of Drugs Act 1971


1. Background

1.1 In October 2001 the Home Secretary asked the Advisory Council on the Misuse of Drugs (the ‘Council’) to review the classification of cannabis preparations in the light of current scientific evidence.

1.2 The Council is established under the Misuse of Drugs Act 1971 to keep under review the drug situation in the United Kingdom and to advise government ministers on the measures to be taken for preventing the misuse of drugs or for dealing with the social problems connected with their misuse. In particular, the Council is required to advise on the appropriate classification of substances being specified under Part I, Part II, and Part III of Schedule 2 to the Act.

1.3 The classification of drugs, in Schedule 2 to the Misuse of Drugs Act 1971, is based on the harm they may cause:

Class A (the most harmful) includes morphine and diamorphine (heroin).

Class B (an intermediate category) includes amphetamines, barbiturates, cannabis and cannabis resin.

Class C (the least harmful) includes anabolic steroids, benzodiazepines and growth hormones.

1.4 When advising on the harmfulness of drugs, the Council takes account of the physical harm that they may cause, their pleasurable effects, associated withdrawal reactions after chronic use, and the harm that misuse may bring to families and society at large.

1.5 The Misuse of Drugs Regulations 2001 (Statutory Instrument 2001/3998) defines the categories of people authorised to supply and possess drugs controlled under the Act. In these Regulations, drugs are categorised under five schedules:

Schedule 1 includes drugs such as cannabis that are not, conventionally, used for medical purposes. Possession and supply are prohibited without specific Home Office approval.

Schedule 2 includes morphine and diamorphine and are subject to special requirements relating to their prescription, safe custody and the need to maintain registers.

Schedule 3 includes barbiturates and are subject to special prescription, though not safe custody requirements.

Schedule 4 includes benzodiazepines and are neither subject to special prescription or safe custody requirements.

Schedule 5 includes preparations that, because of their strength, are exempt from most of the controlled drug requirements.

2.3 This Report considers the most appropriate Class (see paragraph 1.3) into which cannabis preparations should be categorised based on its harmfulness.

2.4 The Report itself is based on a detailed scrutiny of the relevant scientific literature including four reviews commissioned by the Department of Health in 1998 as well as an update commissioned by the Home Office and completed in November 2001.

4. Risks to human health

4.1 Drugs affect health in a number of different ways. They can produce immediate adverse medical effects (such as death from respiratory depression with heroin) or can damage health over a period of time (such as lung and heart disease from smoking tobacco).

4.3.5 Unlike sedative intoxicants such as alcohol, cannabis does not cause respiratory depression or suppress the gag reflex even when extremely intoxicated.

4.3.6 Cannabis differs from alcohol, however, in one major respect: it seems not to increase risk-taking behaviour. This may explain why it appears to play a smaller role than alcohol in road traffic accidents. Cannabis intoxication tends to produce relaxation and social withdrawal rather than the aggressive and disinhibited behaviour commonly found under the influence of alcohol. This means that cannabis rarely contributes to violence either to others or to oneself, whereas alcohol use is a major factor in deliberate self-harm, domestic accidents and violence.

4.4.1 tobacco smoking is the largest single cause of ill health and premature death in the UK. In general cannabis users smoke fewer cigarettes per day than tobacco smokers and most give up in their 30s, so limiting the long-term exposure that we now know is the critical factor in cigarette-induced lung cancer.

4.4.2 Preliminary studies of lung function in regular cannabis smokers have not found a major cause for concern in the majority.

4.4.5 It is possible to rank the risks of dependence of abused drugs with heroin and crack cocaine the worst and cannabis generally at, or near, the bottom (and well below nicotine and alcohol).

4.4.6 The other main concern about the chronic use of cannabis is whether it can lead to mental illness (especially schizophrenia). Although debated for well over a century, no clear causal link has been demonstrated.

4.4.8 There is no evidence that cannabis causes structural brain damage in man.

4.5.1 Tobacco smoking and alcohol use are significant causes of harm to the unborn child. Cannabis may also increase the risk of minor birth defects and abortion but the effect is small.

4.5.2 There is some evidence that smoking cannabis during pregnancy may produce subtle alterations in neuropsychological performance of the child that persists into later life. This effect is similar to that of tobacco smoking and may be due to the actions of tobacco smoke rather than to cannabis per se.

4.5.3 Taken together this data suggest that cannabis use in pregnancy is not safe but that it is probably no more dangerous to the foetus than either alcohol or tobacco.

4.6.2 the use of other substances such as alcohol, tobacco, solvents, stimulants and psychedelic agents ... generally also precedes that of Class A drugs.

4.6.3 other studies have found that the use of alcohol and tobacco in early teens (and especially in pre-adolescents) appears to be associated with the later use of many drugs including cannabis.

4.6.4 it is likely that cannabis use (and that of alcohol or tobacco) has an effect on later Class A drug use.

4.7.1 Cannabis appears not to make as major a contribution to road traffic or other accidents as alcohol.

5.1 The apparent and ready availability of cannabis is, however, disproportionate to the relatively small numbers of people seeking help from drug treatment agencies for cannabis misuse. The high use of cannabis is not associated with major health problems for the individual or society.

5.2 The occasional use of cannabis is only rarely associated with significant problems in otherwise healthy individuals. These harmful effects of cannabis, however, are very substantially less than those associated with similar use of other drugs, such as amphetamines, which (like cannabis) are currently classified as Class B.

5.4 Regular heavy use of cannabis can result in dependence, but its dependence potential is substantially less than that of other Class B drugs such as amphetamines or, indeed, that of tobacco or alcohol.

5.5 It is not possible to state, with certainty, whether or not cannabis use predisposes to dependence on Class A drugs such as heroin or crack cocaine. Nevertheless the risks (if any) are small and less than those associated with the use of tobacco or alcohol.

6.1 Cannabis is not a harmless substance and its use unquestionably poses risks both to individual health and to society.

6.2 Cannabis, however, is less harmful than other substances (amphetamines, barbiturates, codeine-like compounds) within Class B of Schedule 2 to the Misuse of Drugs Act 1971. The continuing juxtaposition of cannabis with these more harmful Class B drugs erroneously (and dangerously) suggests that their harmful effects are equivalent. This may lead to the belief, amongst cannabis users, that if they have had no harmful effects from cannabis then other Class B substances will be equally safe.

6.3 The Council therefore recommends the reclassification of all cannabis preparations to Class C under the Misuse of Drugs Act 1971.



Levels of use (prevalence)

a commonly expressed concern has been that a downward reclassification would lead to an increase in use. In attempting to analyse the likely impact on prevalence of reclassification, there is very little relevant domestic learning to draw on. But it is possible to look at the experience of other countries, albeit in circumstances where civil penalties have replaced criminal sanctions. In particular, the experiences in Australia, the Netherlands and the United States are illustrative. In each of these countries a reduction in the penalties for using cannabis has not led to a significant increase in use.


In announcing any change to the classification of cannabis, it will be important to ensure that the decision and the reasons for it are properly understood. We have tried to express as clearly as we can in this Report the message that cannabis is a harmful drug. But much of the debate about cannabis and about the appropriate response of society to its use tends to overlook this fundamental truth.

More generally, the provision of accurate and objective advice on the health effects of all drugs, and where to access treatment, must be a key part of our drug strategy. In respect of cannabis, the Council hopes that this Report represents a modest contribution to that important goal.