In 2009,  UK drugs advisor Dr. David Nutt was relieved of his duties due to controversial views on the harmfulness of different drugs and the lack of evidence behind current drug policy.

Various claims were that this was politically motivated and concern was that scholarly research such as Nutt's should not be subject to political attack.

Agreed, but a new article in Addiction says the attack was justified because Nutt's work on the harmfulness of drugs is scientifically flawed.

Jonathan Caulkins, Peter Reuter, and Carolyn Coulso 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.

The policy issue is, of course, that 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. 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.

Canadian researchers Benedikt Fischer and Perry Kendall disagree and the primary problem is how to get governments to pay attention to the evidence for drug policies, not to develop more complex rankings that will be ignored: "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."

Addiction researchers believe legal substances (alcohol, tobacco, prescription drugs) are as much a problem as illegal substances, but getting the public to recognize this fact is difficult. Publicizing 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Australian researcher Robin Room argues that all national drug schedules are based on two outdated, pharmacologically-based international drug treaties from 1961 and 1971.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 should be on the official schedules and what to do about them."

Nutt responds to criticism of his science in "Let not the best be the enemy of the good" where he accepts that the 2007 harm-ranking model is imperfect but is an attempt to use scientific evidence in drug policy.

That is a far cry from the beliefs of his defenders who felt like the science was perfect and the motivation was solely political. 

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 so shouldn't be defended at all. 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." 

Fischer and Kendall argue that any country that uses 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."