A 28-week, randomized, controlled trial compared the combination of phentermine and topiramate extended-release (PHEN/TPM ER) with its components as monotherapies and with placebo in obese adults.

Design and Methods

Subjects were randomized to placebo, phentermine 7.5 mg, phentermine 15 mg, topiramate ER 46 mg, topiramate ER 92 mg, PHEN/TPM ER 7.5/46 mg, or PHEN/TPM ER 15/92 mg. All subjects received lifestyle intervention counseling. Primary endpoints were percent weight loss (WL) and achievement of ≥5% WL.


At week 28, PHEN/TPM ER 7.5/46 (−8.5%) and 15/92 (−9.2%) achieved greater percentage WL versus placebo (−1.7%; P < 0.0001) and their respective monotherapies (P < 0.05). The percentage of subjects achieving ≥5% WL was 15.5% for placebo, 43.3% for phentermine 7.5, 46.2% for phentermine 15, 39.2% for topiramate ER 46, 48.6% for topiramate ER 92, 62.1% for PHEN/TPM ER 7.5/46, and 66.0% for PHEN/TPM ER 15/92. PHEN/TPM ER was generally well tolerated; comprehensive assessment of cognitive functions with the Repeatable Battery for Assessment of Neuropsychological Status revealed impairment only in the attention domain.


PHEN/TPM ER demonstrated greater WL when used in combination than when used as monotherapies, suggesting enhanced ability of the combination formulation to induce WL at doses lower than with available monotherapies.