Most marijuana consumers are used to seeing their product as chunks of pungent green plant material coated in sticky, crystallised THC-rich resin.

But if you’re a researcher in the US, looking to work with marijuana – to say, investigate how it impairs people, or how it could help people suffering from certain ailments – you don’t have access to the weed that everyone else is using. Since the late 1960s the US federal government has mandated that all marijuana used in research has to come through the federal government. Read story.