The word marijuana used to be used by everyone in the UK. The word sounds harmless, and is much more pleasant on the ear than the word cannabis, which is rougher and harsher by comparison.
Going back a few years, I noticed a sudden change in police statements reported by the media. They all turned to using the word cannabis instead of marijuana
I'm convinced that the police listened to psychologists who suggested that the use of the harsher-sounding word might help create a different public attitude towards it.