The government has decided to ban all substances that could have a psychoactive effect, including those yet to be invented/discovered, because some of them might be bad for you. Tobacco, alcohol and coffee will be exempt (for now, at least). The intention is to use this sledge-hammer to crack the nut of 'legal highs', but the legal implications are profound.
I've written about it at Spectator Blogs. Do have a read.
Ian Dunt has written an excellent article about the same issue.