Jim Dandy:

The following chart was published in Wikipedia:

http://en.wikipedia.org/wiki/File:Rational_scale_to_assess_the_harm_of_drugs_(mean_physical_harm_and_mean_dependence).svg

Apparently it was published in The Lancet, a medical journal published in the UK. The article can be found here, if you have a subscription to the journal.

http://linkinghub.elsevier.com/retrieve/pii/S0140-6736(07)60464-4

The actual abstract can be read here:

http://www.ncbi.nlm.nih.gov/pubmed/17382831

It is very interesting. They used 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". They generated a chart to correlate dependence and physical harm. Two groups of experts independently assessed the data. (Read the abstract)

In that chart cannabis is causes less dependence and less harm than tobacco or alcohol. Tobacco causes almost as much dependence as cocaine, but it is less harmful than cocaine. The worst drug is heroin. I think that the medical profession is working towards a better understanding of what drugs effects are and how that can be applied in a regulatory system.