Adipex Phentermine (Adipex P) diet pill is a prescription diet pill that is used to help people lose weight who are obese (have a Body Mass Index of 30 or higher) or have serious health risks due to their size. It is more commonly known by the brand name Phentermine. It works as an appetite suppressant. It is taken in conjunction with certain food requirements and an exercise program. Adipex P is only used for a few weeks (less than 12 weeks) since its effectiveness decreases with prolonged use. The drug is taken one time each day either in the morning or 10 hours before bedtime, because of its known effects of interrupting sleep. You should take Adipex P only and exactly how it was directed to you by your physician.