˝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.
The results of this study do not provide justiﬁcation for the sharp A, B, or C divisions of the current classiﬁcations in the UK Misuse of Drugs Act. Distinct categorisation is, of course, convenient for setting of priorities for policing, education, and social support, as well as to determine sentencing for possession or dealing. But neither the rank ordering of drugs nor their segregation into groups in the Misuse of Drugs Act classification is supported by the more complete assessment of harm described here. Sharply defined categories in any ranking system are essentially arbitrary unless there are obvious discontinuities in the full set of scores. Results show only a hint of such a transition in the spectrum of harm, in the small step in the very middle of the distribution, between buprenorphine and cannabis. Interestingly, alcohol and tobacco are both in the top ten, higher-harm group. There is a rapidly accelerating harm value from alcohol upwards. So, if a three-category classification were to be retained, one possible interpretation of our findings is that drugs with harm scores equal to that of alcohol and above might be class A, cannabis and those below might be class C, and drugs in between might be class B. In that case, it is salutary to see that alcohol and tobacco —the most widely used unclassified substances— would have harm ratings comparable with class A and B illegal drugs, respectively.
Our findings raise questions about the validity of the current Misuse of Drugs Act classification, despite the fact that it is nominally based on an assessment of risk to users and society. The discrepancies between our findings and current classifications are especially striking in relation to psychedelic-type drugs. Our results also emphasise that the exclusion of alcohol and tobacco from the Misuse of Drugs Act is, from a scientific perspective, arbitrary. We saw no clear distinction between socially acceptable and illicit substances. The fact that the two most widely used legal drugs lie in the upper half of the ranking of harm is surely important information that should be taken into account in public debate on illegal drug use. Discussions based on a formal assessment of harm rather than on prejudice and assumptions might help society to engage in a more rational debate about the relative risks and harms of drugs.
We believe that a system of classification like ours, based on the scoring of harms by experts, on the basis of scientific evidence, has much to commend it. Our approach provides a comprehensive and transparent process for assessment of the danger of drugs, and builds on the approach to this issue developed in earlier publications but covers more parameters of harm and more drugs, as well as using the delphic approach, with a range of experts. The system is rigorous and transparent, and involves a formal, quantitative assessment of several aspects of harm. It can easily be reapplied as knowledge advances. We note that a numerical system has also been described by MacDonald and colleagues to assess the population harm of drug use, an approach that is complementary to the scheme described here, but as yet has not been applied to specific drugs. Other organisations (eg, the European Monitoring Centre for Drugs and Drug Addiction and the CAM committee of the Dutch government) are currently exploring other risk assessment systems, some of which are also numerically based. Other systems use delphic methodology, although none uses such a comprehensive set of risk parameters and no other has reported on such a wide range of drugs as our method. We believe that our system could be developed to aid in decision-making by regulatory bodies—eg, the UK’s Advisory Council on the Misuse of Drugs and the European Medicines Evaluation Agency—to provide an evidence-based approach to drug classification.˝
—David Nutt, Leslie A King, William Saulsbury, Colin Blakemore