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Psychiatry Investig > Volume 20(9); 2023 > Article
Psychiatry Investigation 2023;20(9):799-807.
DOI:    Published online September 19, 2023.
The Use of Phentermine for Obesity in Psychiatric Patients With Antipsychotics
Eunju Kim1,2  , Daniel Rim1  , Jeong-Hun Shin1,3  , Denise Wong1  , Dong Wook Kim1 
1Section of Endocrinology, Diabetes and Weight Management, Boston University, Boston University Chobanian & Avedisian School of Medicine, Boston, MA, USA
2Mood Disorder Clinic and Affective Neuroscience Laboratory, Department of Psychiatry, Seoul National University Bunding Hospital, Seongnam, Republic of Korea
3Department of Internal Medicine, Hanyang University College of Medicine, Seoul, Republic of Korea
Correspondence: Dong Wook Kim ,Tel: +1-617-638-8547, Fax: +1-617-638-8599, Email:
Received: February 10, 2023   Revised: May 1, 2023   Accepted: June 14, 2023   Published online: September 19, 2023
Phentermine is a commonly used weight-loss agent in the United States, but there is a little information about the use of phentermine for patients with obesity taking antipsychotic medications.
We gathered 57 patients with obesity taking antipsychotic medications whose phentermine treatment was simultaneous with or after any type of antipsychotic exposure and collected data of clinical information, initial/follow-up anthropometric variables, and adverse events (AEs) for the 6-month study period.
In total, the mean body weight reduction (BWR) was 4.45 (7.04) kg, and the mean BWR percent (BWR%) was 3.92% (6.96%) at 6 months. Based on the response to phentermine, the patients were classified into two groups: the responder (n=25; BWR% ≥5%) and nonresponder (n=32; BWR% <5%) groups. The responder group’s mean BWR and BWR% were 10.13 (4.43) kg and 9.35% (4.09%), respectively, at 6 months. The responders had higher rates of anticonvulsant combination therapy (ACT; responder, 72.0% vs. non-responder, 43.8%; p=0.033) and a shorter total antipsychotic exposure duration (responder, 23.9 [16.9] months vs. non-responder, 37.2 [27.6] months; p= 0.039). After adjusting age, sex, and initial body weight, ACT maintained a significant association with phentermine response (odds ratio=3.840; 95% confidence interval: 1.082–13.630; p=0.037). In the final cohort, there was no report of adverse or new-onset psychotic symptoms, and the common AEs were sleep disturbances, dry mouth, and dizziness.
Overall, phentermine was effective and tolerable for patients with obesity taking antipsychotic medications, and ACT (predominantly topiramate) augmented the weight-loss effect of phentermine.
Key words   Phentermine; Antipsychotics; Topiramate; Obesity; Safety


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