American singer Willie Nelson uses marijuana to judge the quality of the new melodies he writes. The 73-year-old has smoked cannabis for most of his adult life and is a campaigner to have the drug legalised. And he insists smoking joints helps rather than hinders his songwriting. He says, "I figured if it wasn't worth remembering it probably wasn't a very good song, so that would be the test, to see if I remembered it (after smoking a joint and) got back to a guitar or a piano. "That was usually a pretty good measuring stick, but I'm sure I forgot a few that might have been OK."