The same thing happened to me. I say about a week and half after I started taking the pills I broke out in hives to. i took them 2 3 years ago and didn't have any problems. Learn how to use Phentermine (the right way) in this patient-centered guide. You will learn how to use it safely, the potential side effects associated with its use, why most people use it wrong and more. Phentermine is the most widely-prescribed weight-loss medication in the United States. It first received FDA approval in 1959 as an appetite suppressant for the short-term management of obesity. Learn about Adipex-P (Phentermine Hydrochloride) may treat, uses, dosage, side effects, drug interactions, warnings, patient labeling, reviews, and related medications. Phentermine, an amphetamine congener, is the most widely used anti-obesity drug in the U.S. Although phentermine is the agent-of-choice among physicians specializing in obesity treatment, the use of this drug for obesity treatment by other physicians has long been curtailed because misapprehensions regarding phentermine safety. Phentermine is a prescription weight-loss drug. Most doctors agree that phentermine works by suppressing the appetite and upregulating the metabolism, though the specific pathways are not fully understood. The limited usefulness of agents of this class, including Phentermine, [see Clinical Pharmacology (12.1, 12.2)] should be measured against possible risk factors inherent in their use such as those described below. Phentermine is an appetite suppressant used together with diet and exercise to treat obesity. Learn about side effects, interactions and indications. A: Phentermine (Adipex-P, Ionamen) when used properly under strict supervision of your health care provider for short time use, has shown to help with weight loss. 5 WARNINGS AND PRECAUTIONS 5.1 Coadministration With Other Drug Products for Weight Loss ADIPEX-P® is indicated only as short-term (a few weeks).