"What is Fastin? – Fastin is a drug that was “based” on a drug called Phentermine; however, Fastin falls short by only containing 37.5g of ß-methyl-phenethylamine. Further, this pretender drug claims to be a “mood promoter” yet this product lacks important ingredients such as Synephrine and b12 which aid in weight loss. Oddly enough, the Fastin website lists extensive details about Phentermine, leading consumers to believe it is actually the same product. After looking into this product, consumers will find that Fastin is not the same as Phentermine and will discover additional negative aspects."
Phentermine is still a prescription drug only and not sold over-the-counter. The over-the-counter ones are knock-offs and the ones that try to come across as being phentermine, have usually changed a few letters of the word, if you look closely. I don't even know how this particular company even got away with using the brand name of Fastin, as this is also a brand name of one of (the brands of) REAL prescription phentermine.
These types of things are basically mis-representations, done intentionally, as a marketing ploy.