Effectiveness and predictors of weight loss response to phentermine plus lifestyle modifications among youth in a paediatric weight management clinical setting

Background: Anti-obesity medications (AOMs) are promising lifestyle modification (LSM) adjuncts for obesity treatment, and phentermine is commonly prescribed in paediatric weight management clinics. Determining 'real-world' AOM effectiveness and characteristics predicting response is important. Objectives: We sought to describe phentermine plus LSM effectiveness and identify baseline characteristics predicting response. Methods: This was a retrospective cohort study among youth seen in a US academic-based weight management clinic from 2012 to 2020. Baseline characteristics (e.g., body mass index (BMI), liver transaminases, eating-related behaviours) and outcomes (%BMI of 95th percentile (%BMIp95), BMI, %BMI change, weight) were determined through electronic health records and intake surveys. Results: Among 91 youth prescribed phentermine plus LSM over 8 years (mean %BMIp95 150%), %BMIp95 was statistically significantly reduced at 1.5, 3, 6 and 12 months (peak reduction 10.9 percentage points at 6 months; p < 0.001). Considering multiple comparisons, the presence of baseline elevated alanine aminotransferase was associated with statistically significant smaller 1.5-month %BMIp95 reductions (p = 0.001) and higher food responsiveness with smaller 3- (p = 0.001) and 6-month (p < 0.001) reductions. Conclusions: Phentermine plus LSM reduced %BMIp95 among youth in a weight management clinic, and baseline characteristics may help determine those more or less likely to respond. Prospective studies are needed to further characterize effectiveness and confirm response predictors.