Introduction: Phentermine, the most used anti-obesity medication in the United States, has been limited in worldwide use because of a fear of addiction potential, given its relation to amphetamine. However, there have been no studies on phentermine addiction published. This study was undertaken to examine phentermine's addiction potential, particularly with long-term use.
Methods: The 18-item Kampman Cocaine Selective Severity Assessment was modified; the word “phentermine” was used in place of the word “cocaine” to create the Phentermine Selective Severity Assessment (PSSA). The study used PSSA on 35 patients in a weight management program who all voluntarily and abruptly stopped taking phentermine, and a control group of 35 patients who had not yet undergone any treatment.
The Kampman scale had also been previously modified for amphetamine addiction as a way to assess withdrawal symptoms. It was hypothesized that if phentermine had addiction potential (as does amphetamine), then patients should experience some of the same withdrawal symptoms.
Results: Data from each group—treated and untreated—were compared with each other using a t test. The data on the two groups in this study was then compared with already-published data on amphetamine patients who were addicted and underwent withdrawal.
No significant differences were seen between the treated and untreated patients in individual items or in total scores.
However, when comparing the amphetamine-addicted patients and the phentermine-treated patients, there were significant differences. The hallmark withdrawal symptom—craving for the abused substance—was entirely absent in the phentermine-treated patients.
Conclusions: This study showed that abruptly stopping phentermine treatment does not lead to withdrawal. Additionally, long-term use does not lead to cravings of phentermine. Of note, the study also documented that phentermine cessation does lead to the loss of its therapeutic effect, and patients regain weight.
Commentary by J. Michael Gonzalez-Campoy MD, PhD, FACESee Dr. Gonzalez-Campoy's commentary in the introduction.