When seeing data that's years old, one immediately asks whether the data is still valid, or if it was any good in the first place. The second question is not necessarily fair to the scientists who've worked very hard to develop the data, but in the hyper-partisan world of cannabis still trying to drag itself out of Reefer Madness days, it's one that needs to be asked.
In March 2007, Professor David Nutt, PhD, along with three colleagues (Leslie King, PhD, William Saulsbury, MA and Professor Colin Blakemore, FRS) published "Development of a Rational Scale to Assess the Harm of Drugs of Potential Misuse" in The Lancet, one of the world's most respected medical journals. The article includes 26 additional references to previously published articles about relevant topics. (The full article in PDF format (including graphics) can be seen here.)
The study was a review of drugs in the United Kingdom. As in the US, the impact of drugs on society is substantial. "In the UK, the total burden of drug misuse, in terms of health, social, and crime-related costs, has been estimated to be between £10 billion and £16 billion per year, with the global burden being proportionately enormous." For reference about scale, the US has approximately 5x as many people as the UK.
In this research, drugs are categorized based on "three main factors that together determine the harm associated with any drug of potential abuse: the physical harm to the individual user caused by the drug; the tendency of the drug to induce dependence; and the effect of drug use on families, communities, and society."
Interestingly, the study ventured outside the drugs categorized in the UK's Misuse of Drugs Act, which correlates the US' Schedule of Controlled Substances, to assess steroids, khat, nicotine and alcohol. It was felt that "systematic consideration of the safety margin of the drug in terms of its acute toxicity, as well as its likelihood to produce health problems in the long term.... Tobacco and alcohol have a high propensity to cause illness and death as a result of chronic use... Tobacco and alcohol together account for about 90% of all drug-related deaths in the UK."
The ranking of addictiveness of the drugs measured in 2007 is as follows:
Readers of the American Cannabis Report will quickly note that deadly alcohol made the list while cannabis is not even among the Top 10 as measured by median scores. They will also want to know why data showing cannabis' lesser danger as compared to many other substances was not prominently shared in the past decade while authorities were enforcing ever-heavier penalties for cannabis possession, arresting millions in the US alone.
In 2018, the List of Five Most Addictive Drugs goes like this:
Opioid Drugs including heroin, oxycodone, hydrocodone
Cocaine including crack cocaine
Benzodiazepines (Xanax, Valium, Atavin, Klonopin, e.g)