Background

Phentermine is a widely used medication to treat obesity. However, there is a perception that phentermine pharmacotherapy may increase blood pressure (BP) and cardiovascular risk. The aim of this study is to assess the impact of phentermine on BP among patients who participated in a non-surgical medical weight management program.

Methods

A sample of 318 overweight and obese participants aged 18 years or older was analyzed (phentermine-treated group=208, phentermine-untreated group=110). Phentermine-treated patients were further stratified by their hypertension status. Wilcoxon Singed Rank test was used to assess the change in percentage weight loss and blood pressure.

Results

We found significant reduction in BP and greater percentage weight loss as patients progressed in the program. Patients in the phentermine-treated group had reductions in systolic BP (SBP) and diastolic BP (DBP) at week2 (-2*,-0.8*), week3 (-2.8, -1.2), week4 (-5.6, -2.8), week8 (-3.3, -1.2*), week12 (-5.2,-2.9), week26 (-5.2, -1.9), week40 (-4.4, -1.6), and week52 (-4.1,-1.5). Patients in the phentermine-untreated group had reductions in SBP and DBP at week2 (-2.9, -1.7*), week3 (-4.2, -1.5*), week4 (-4.5, -2.0), week8 (-3.7, -1.7), week12 (-6.2, -2.8), week26 (-5.8, -2.8), week40 (-5.76, -3.0), and week52 (-5.8, -2.7). Additionally, we observed a mild and statistically significant increase in BP among phentermine-treated normotensive patients through 52 weeks.[*p>0.05]

Conclusions

We initially observed results that suggest phentermine pharmacotherapy is not associated with increase in BP; however, an additional nested analysis stratified by hypertension status unveiled a notable cohort effect that shows an increase in BP among phentermine-treated normotensive patients.