Phentermine is the name of an active ingredient in prescription weight loss pills, while Adipex is a popular brand of phentermine weight loss pills.
Phentermine is the name of both the generic medication and the active ingredient in phentermine tablets and capsules. It is manufactured by a range of pharmaceutical companies.
Adipex-P, on the other hand, is a brand weight loss medication. Adipex 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 branded pill, Adipex is often more expensive than generic phentermine.
→ To learn more about phentermine weight loss pills, read the phentermine ultimate guide.