A study of abrupt phentermine cessation in patients in a weight management program.

Phentermine is the most widely used antiobesity drug in the United States. Although no evidence of phentermine addiction has been published, fear that phentermine has addiction potential has contributed to curtailment of its worldwide use in clinical practice. The aim of this study was to evaluate the abuse and addiction potential of long-term phentermine pharmacotherapy in patients in a weight management program. Thirty-five patients in a weight management program who abruptly stopped taking prescribed phentermine on their own initiative were examined using the 18-item Kampman Cocaine Selective Severity Assessment scale modified for phentermine. The Kampman Cocaine Selective Severity Assessment scale has also been modified by McGregor for amphetamines to assess withdrawal from amphetamine in amphetamine-addicted subjects. For comparison, 35 new patients were examined with the same scale before any treatment was initiated. Data from the treated and untreated groups were compared by t test with each other and with published data from amphetamine-addicted subjects. There were no significant differences in individual items or total scores between the patients who stopped phentermine abruptly and the patients who had never taken phentermine. There was a striking and significant difference in individual and total scores between the phentermine-treated subjects and the amphetamine-dependent subjects. Cravings for the substance abused, the hallmark characteristic of substance dependence and withdrawal, were entirely absent in the phentermine-treated subjects. Abrupt cessation of long-term phentermine therapy does not induce amphetamine-like withdrawal. Long-term phentermine therapy does not induce phentermine cravings. Symptoms observed after abrupt phentermine cessation represent loss of therapeutic effect and are not withdrawal.