I use Grazon 90 - but it's best if you can hack it back first and then spray the young regrowth (otherwise it'll cost you a fortune - you have to DRENCH the ruddy stuff!) You will still get some regrowth after apparently killing it - so - like bracken - you have to keep at it!
Sorry, couldn't resist! If you hack at the base, it takes years to grow back. Can't say it's a bush that offends, me, though. It's quite pretty as long as you don't land in it!!
Only sure way is to dig it up and then spray the ground; even then you might get a few sprigs back, sorry. Birds, bees and insects love it so it does have a job the same as nettles.