English to Polish Medical Medical: Health Care shopoholism

I have got a problem with thranslation of this particular phrase. Pwn's explanation seems to be inadequate i.e. extraneous as (outside) zewnętrzny or (not essential) nieistotny... My own guess was "dodatkowe/zbyteczne zakupy".

The whole context for the phrase: "people tend to make more extraneous purchases when they shop outside their own communities"

Thnx for your help