Even the WeightWatchers community chat website had more than 80 message-board entries in which users talked about using phentermine - also commonly sold online under the brand names Duromine, Ionamine, what is Adipex and Fastin. what is Adipex diet drug with Phentermine HCl, should not be mistaken as a substitute for food. Use this weight loss medication under proper medical supervision, as it is habit-forming drug and can make you physically and psychologically reliant.