Phentermine is the name of both the medication and the active ingredient in phentermine tablets and capsules, and is manufactured by a range of pharmaceutical companies. Adipex, officially known as Adipex-P, is a brand weight loss medication, which also contains phentermine as the active ingredient and is manufactured by GATE Pharmaceuticals - now part of Teva Pharmaceuticals. Phentermine, as the active ingredient, is exactly the same in both generic phentermine and branded phentermine.
As a brand, Adipex is often more expensive than generic phentermine, however, generic phentermine diet pills are bioequivalent to brand name phentermine. This means that the strength, safety, quality, performance characteristics, dosage form and route of administration are exactly the same as the brands, such as Adipex, which contain phentermine.