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Qual Life Res. 2016 May;25(5):1237-44. doi: 10.1007/s11136-015-1153-x. Epub 2015 Oct 7.

Health-related quality of life in two randomized controlled trials of phentermine/topiramate for obesity: What mediates improvement?

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Department of Community and Family Medicine, Duke University School of Medicine, Durham, NC, USA.
Quality of Life Consulting, 732 Ninth Street #563, Durham, NC, 27705, USA.
Department of Health Studies, Sogn og Fjordane University College, Førde, Norway.
Morbid Obesity Centre, Vestfold Hospital Trust, Tønsberg, Norway.
Pennington Biomedical Research Centre, Baton Rouge, LA, USA.
VIVUS, Inc., Mountain View, CA, USA.
Neuropsychiatric Research Institute, Fargo, ND, USA.
Department of Psychiatry and Behavioral Science, University of North Dakota School of Medicine and Health Sciences, Fargo, ND, USA.



Phentermine/topiramate combination therapy resulted in significant weight loss and improvements in cardiometabolic risk factors in patients with obesity/overweight in two published 56-week randomized, placebo-controlled trials (EQUIP and CONQUER). The purpose of the current study was to examine whether phentermine/topiramate is also associated with greater improvements in health-related quality of life (HRQOL) and whether HRQOL improvements are solely attributable to weight reduction.


Patients in EQUIP (n = 751) had a body mass index (BMI) ≥ 35 with no obesity-related comorbidity. Patients in CONQUER (n = 1623) had a BMI ≥ 27 and ≤ 45 and at least two obesity-related comorbid conditions. HRQOL was assessed with Impact of Weight on Quality of Life-Lite (IWQOL-Lite) and Medical Outcomes Study Short Form (SF-36) (CONQUER only).


Significant improvements in both obesity-specific and physical HRQOL were observed at 56 weeks in both trials (p < .0001). In EQUIP, BMI reduction fully mediated improvements in IWQOL-Lite total score (p < .0001). In CONQUER, both BMI reduction (all p values < .0001) and change in depressive symptoms (all p values < .025) were significant mediators of improved IWQOL-Lite total score and SF-36 Physical Component Summary score. Gender, psychiatric history, and baseline triglycerides moderated these relationships.


Both trials demonstrated that treatment with phentermine/topiramate improved HRQOL compared with placebo. Although reduction in BMI accounted for the majority of improvements in obesity-specific and physical HRQOL, decrease in depressive symptoms was also a significant mediator. Results highlight the predominance of weight reduction as a key factor in improving HRQOL in obesity.


Health-related quality of life; Impact of Weight on Quality of Life-Lite (IWQOL-Lite); Mediation analysis; Phentermine/topiramate; Short-Form-36 (SF-36); Weight loss

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