Drug misuse and abuse are major health problems. Harmful drugs are regulated according to classification systems that purport to relate to the harms and risks of each drug. However, the methodology and processes underlying classification systems are generally neither specified nor transparent, which reduces confidence in their accuracy and undermines health education messages. We developed and explored the feasibility of the use of a nine-category matrix of harm, with an expert delphic procedure, to assess the harms of a range of illicit drugs in an evidence-based fashion. We also included five legal drugs of misuse (alcohol, khat, solvents, alkyl nitrites, and tobacco) and one that has since been classified (ketamine) for reference. The process proved practicable, and yielded roughly similar scores and rankings of drug harm when used by two separate groups of experts. The ranking of drugs produced by our assessment of harm differed from those used by current regulatory systems. Our methodology offers a systematic framework and process that could be used by national and international regulatory bodies to assess the harm of current and future drugs of abuse.

Panel 1
Evaluation criteria and their definitions
Drug-specific mortality
Intrinsic lethality of the drug expressed as ratio of lethal dose and standard dose (for adults)
Drug-related mortality
The extent to which life is shortened by the use of the drug (excludes drug-specific mortality)—eg, road traffic accidents, lung cancers, HIV, suicide
Drug-specific damage
Drug-specific damage to physical health—eg, cirrhosis, seizures, strokes, cardiomyopathy, stomach ulcers
Drug-related damage
Drug-related damage to physical health, including consequences of, for example, sexual unwanted activities and self-harm, blood-borne viruses, emphysema, and damage from cutting agents
Dependence
The extent to which a drug creates a propensity or urge to continue to use despite adverse consequences (ICD 10 or DSM IV)
Drug-specific impairment of mental functioning
Drug-specific impairment of mental functioning—eg, amfetamine-induced psychosis, ketamine intoxication
Drug-related impairment of mental functioning
Drug-related impairment of mental functioning—eg, mood disorders secondary to drug-user's lifestyle or drug use
Loss of tangibles
Extent of loss of tangible things (eg, income, housing, job, educational achievements, criminal record, imprisonment)
Loss of relationships
Extent of loss of relationship with family and friends
Injury
Extent to which the use of a drug increases the chance of injuries to others both directly and indirectly—eg, violence (including domestic violence), traffic accident, fetal harm, drug waste, secondary transmission of blood-borne viruses
Crime
Extent to which the use of a drug involves or leads to an increase in volume of acquisitive crime (beyond the use-of-drug act) directly or indirectly (at the population level, not the individual level)
Environmental damage
Extent to which the use and production of a drug causes environmental damage locally—eg, toxic waste from amfetamine factories, discarded needles
Family adversities
Extent to which the use of a drug causes family adversities—eg, family breakdown, economic wellbeing, emotional wellbeing, future prospects of children, child neglect
International damage
Extent to which the use of a drug in the UK contributes to damage internationally—eg, deforestation, destabilisation of countries, international crime, new markets
Economic cost
Extent to which the use of a drug causes direct costs to the country (eg, health care, police, prisons, social services, customs, insurance, crime) and indirect costs (eg, loss of productivity, absenteeism)
Community
Extent to which the use of a drug creates decline in social cohesion and decline in the reputation of the community
ICD 10=International Classification of Diseases, tenth revision. DSM IV=Diagnostic and Statistical Manual of Mental Disorders, fourth revision.
Scoring of the drugs on the criteria
Drugs were scored with points out of 100, with 100 assigned to the most harmful drug on a specific criterion. Zero indicated no harm. Weighting subsequently compares the drugs that scored 100 across all the criteria, thereby expressing the judgment that some drugs scoring 100 are more harmful than others.
In scaling of the drugs, care is needed to ensure that each successive point on the scale represents equal increments of harm. Thus, if a drug is scored at 50, then it should be half as harmful as the drug that scored 100. Because zero represents no harm, this scale can be regarded as a ratio scale, which helps with interpretation of weighted averages of several scales. The group scored the drugs on all the criteria during the decision conference.
Consistency checking is an essential part of proper scoring, since it helps to minimise bias in the scores and encourages realism in scoring. Even more important is the discussion of the group, since scores are often changed from those originally suggested as participants share their different experiences and revise their views. Both during scoring and after all drugs have been scored on a criterion, it is important to look at the relativities of the scores to see whether there are any obvious discrepancies.

Study design

The analysis was undertaken in a two-stage process. The choice of harm criteria was made during a special meeting in 2009 of the UK Advisory Council on the Misuse of Drugs (ACMD), which was convened for this purpose. At this meeting, from first principles and with the MCDA approach, members identified 16 harm criteria (figure 1). Nine relate to the harms that a drug produces in the individual and seven to the harms to others both in the UK and overseas. These harms are clustered into five subgroups representing physical, psychological, and social harms. The extent of individual harm is shown by the criteria listed as to users, whereas most criteria listed as to others take account indirectly of the numbers of users. An ACMD report explains the process of developing this model.6

In June, 2010, a meeting under the auspices of the Independent Scientific Committee on Drugs (ISCD)—a new organisation of drug experts independent of government interference—was convened to develop the MCDA model and assess scores for 20 representative drugs that are relevant to the UK and which span the range of potential harms and extent of use. The expert group was formed from the ISCD expert committee plus two external experts with specialist knowledge of legal highs (webappendix). Their experience was extensive, spanning both personal and social aspects of drug harm, and many had substantial research expertise in addiction. All provided independent advice and no conflicts of interest were declared. The meeting's facilitator was an independent specialist in decision analysis modelling. He applied methods and techniques that enable groups to work effectively as a team, enhancing their capability to perform,7 thereby improving the accuracy of individual judgments. The group scored each drug on each harm criterion in an open discussion and then assessed the relative importance of the criteria within each cluster and across clusters. They also reviewed the criteria and the definitions developed by the ACMD. This method resulted in a common unit of harm across all the criteria, from which a new analysis of relative drugs harms was achieved. Very slight revisions of the definitions were adopted, and panel 1 shows the final version.
Panel 1
Evaluation criteria and their definitions
Drug-specific mortality
Intrinsic lethality of the drug expressed as ratio of lethal dose and standard dose (for adults)
Drug-related mortality
The extent to which life is shortened by the use of the drug (excludes drug-specific mortality)—eg, road traffic accidents, lung cancers, HIV, suicide
Drug-specific damage
Drug-specific damage to physical health—eg, cirrhosis, seizures, strokes, cardiomyopathy, stomach ulcers
Drug-related damage
Drug-related damage to physical health, including consequences of, for example, sexual unwanted activities and self-harm, blood-borne viruses, emphysema, and damage from cutting agents
Dependence
The extent to which a drug creates a propensity or urge to continue to use despite adverse consequences (ICD 10 or DSM IV)
Drug-specific impairment of mental functioning
Drug-specific impairment of mental functioning—eg, amfetamine-induced psychosis, ketamine intoxication
Drug-related impairment of mental functioning
Drug-related impairment of mental functioning—eg, mood disorders secondary to drug-user's lifestyle or drug use
Loss of tangibles
Extent of loss of tangible things (eg, income, housing, job, educational achievements, criminal record, imprisonment)
Loss of relationships
Extent of loss of relationship with family and friends
Injury
Extent to which the use of a drug increases the chance of injuries to others both directly and indirectly—eg, violence (including domestic violence), traffic accident, fetal harm, drug waste, secondary transmission of blood-borne viruses
Crime
Extent to which the use of a drug involves or leads to an increase in volume of acquisitive crime (beyond the use-of-drug act) directly or indirectly (at the population level, not the individual level)
Environmental damage
Extent to which the use and production of a drug causes environmental damage locally—eg, toxic waste from amfetamine factories, discarded needles
Family adversities
Extent to which the use of a drug causes family adversities—eg, family breakdown, economic wellbeing, emotional wellbeing, future prospects of children, child neglect
International damage
Extent to which the use of a drug in the UK contributes to damage internationally—eg, deforestation, destabilisation of countries, international crime, new markets
Economic cost
Extent to which the use of a drug causes direct costs to the country (eg, health care, police, prisons, social services, customs, insurance, crime) and indirect costs (eg, loss of productivity, absenteeism)
Community
Extent to which the use of a drug creates decline in social cohesion and decline in the reputation of the community
ICD 10=International Classification of Diseases, tenth revision. DSM IV=Diagnostic and Statistical Manual of Mental Disorders, fourth revision.