kiwi drug is legally selling codeine, because in new zealand it is legal to sell codeine in certain dosages over the counter, with certain regulations. i noticed they have you fill out a questionaire before ordering, specifying what you use it for. this satisifies the authorities. also they put limits on how much you can order.
that said the US government goes back and forth on what you can import from other countries, but this isnt specific to codeine. even if you are 80 years old and order lipitor from canada its technically "not legal" but its probably comparable to crossing and undotted white line on a road while driving
the us government (fda) has stated that while these things may not be legal they will not prosecute importers of medications legal in other countries as long as its for personal consumption, hence the limits