Having an "exceptions list" system is depressingly silly. Basically this law will mean the police *can* arrest almost anyone, because almost everyone will be technically in possession of *something* illegal. Which is a bad starting point.
Also, most people who die from these things have been sold them illegally already. Most "legal highs" that are dangerous are sold as inedible chemicals, so either a) the person taking them knew they weren't supposed to be consumed or b) the provider was already breaking the law.
I'm with Glaurung on the decriminalisation issue. I'd say things like weed should be fully legalised, whereas harder drugs should be a matter for compulsory healthcare/treatment. Education and rehabilitation are in some ways the most important thing - but decriminalisation would free up the funds from the policy to actually put into caring for addicts, and allow cops to focus their remaining drug funds much more heavily on chasing down high-level supply criminals rather than requiring them to bust some fifty year old bloke who grows a small amount of cannabis in his back garden.
