I just filled a script for phentermine 37.5 @ a costco pharmacy. I was asked if I wanted a generic, I said yes! To begin with, I thought "phentermine" was a generic for a few other brand name drugs. But what I bought isn't exactly the same as my last script; (phentermine cac vs. phen. kvk, by looks and formulation.) I haven't taken it yet but i'm concerned that it will not have the effectivness I need. Is this: "a generic for a generic," or what...?