Revisiting the David Nutt debate: Is it possible to rank different drugs by the harm they cause?

American researchers Jonathan Caulkins, Peter Reuter, and Carolyn Coulson argue that Nutt erred by assuming that drug-related harms can be reduced to a single dimension. Most such rankings combine individual harms and harms to society. But national drug policies aim to reduce harm to society, so combined scores may be misleading. Furthermore, it is not for scientists alone to decide the relative weights society should place on such disparate drug-related harms as dependence, overdose death, and corruption. Caulkins and colleagues also argue that even perfect ratings of substances' current harm to society would not be useful, because harm is governed by the interaction between substance and policy; it is not a property of the chemical alone. Policymakers need analytical tools that show the likely changes in different types of harm associated with each change in drug policy.

Addiction hosts a spirited international debate about these critiques, including a response from Dr. Nutt himself.

Canadian researchers Benedikt Fischer and Perry Kendall argue that there is no benefit to categorically knocking down the work of Nutt and his colleagues when current global drug control policy pays scientific evidence no heed. The primary problem at hand is to get governments to pay attention to the evidence for drug policies, not to develop more complex rankings that will be ignored. Fischer and Kendall state, "If we assume public health and welfare should be guiding principles for substance control policy, we would not expect to see the third most commonly used drug (cannabis) to be scheduled and regulated alongside drugs like heroin and cocaine, while alcohol and tobacco are not only legally available, but are openly traded and lead to thousands of cases of deaths and injuries each year."

This view is supported by Norwegian researcher Ingeborg Rossow. She argues that Norwegian policymakers' views reflect those of the general public: illegal substances constitute a larger problem than alcohol, which justifies strict control of illegal drugs and liberalization of alcohol control. Addiction researchers know that legal substances (alcohol, tobacco, prescription drugs) are as much a problem as illegal substances, but getting the public to recognize this fact is difficult. Publicising reports on the relative size of harms from legal and illegal substances may help to change public opinion.

Australian researcher Robin Room argues that all national drug schedules are based on two outdated, pharmacologically-based international drug treaties from 1961 and 1971. By ranking drugs in the light of changes in knowledge and understanding since then, Nutt and colleagues have "started a debate which is long overdue."

"The priority of the debate" Room argues, "should be on the official schedules and what to do about them."

Isidore Obot, a Nigerian researcher, embraces the idea of developing more complex policy tools, because more refined ranking systems will produce more useful information for policymakers. The value of the model developed by Nutt and colleagues lies in the improvements future researchers will make to it.

David Nutt's defence is expressed in his Voltairian title, "Let not the best be the enemy of the good." Nutt accepts that the 2007 harm-ranking model is imperfect but argues that it is nonetheless a good attempt to use scientific evidence in drug policy. Says Nutt: "we have provided the best currently available analysis of an extremely complex multifaceted data set. It ain't perfect but is nevertheless good enough to be useful." Nutt also explains that his simplified look at drug harms provides policymakers with a tool of the type they use: "All decisions regarding drug classifications resolve harms into a single scale point for each drug, so people, particularly politicians, are used to making and working with such estimations."

Caulkins, Reuter, and Coulson respond by restating that the current methods of ranking drugs by harm are conceptually and methodologically unsound. Defending them on the grounds that that simplification is required is equally unsound. We need better methods for understanding the complex network of individual and aggregate harms. "[If] the public has trouble grasping multi-dimensional scales, that should be seen as a hurdle to overcome, not a restraint that needs to be accepted."

The final word should perhaps go to Fischer and Kendall, who argue that any country that uses these admittedly flawed and limited harm scales to inform public policy will experience a "quantum leap of progress" toward evidence-based drug policy. They state that "The benefits from grounding drug control policy in Nutt et al.'s harm scales could be expected to be tangible and last until well after their critics have revised and improved them."