Diet Drugs Phentermine and Topiramate Weight Loss Study

Obesity is associated with reduced life span and increased chances of death by heart failure, cancer and many other disorders. However, diet and lifestyle changes can reduce obesity. In this study, the effects of controlled doses of phentermine and topiramate on the health of obese people are examined. Groups of participants were given a placebo, or a daily single or double dose of the two drugs phentermine and topiramate. After 56 weeks, the groups that received the drug treatment showed marked weight loss. Some adverse side effects were seen, though not critical ones. The drug combination of phentermine and topiramate was found effective in treating obesity, along with the right changes in diet and lifestyle.

About 90% of type 2 diabetes patients are obese and the blood pressure (BP) of these people is about five-to-six times higher than those with normal weight. Weight reduction of 5-10% in patients with diabetes has a beneficial effect on various other ailments associated with obesity, such as improved levels of blood sugar, cholesterol, and BP. Effective administration of drugs together with counseling helps in improved weight management. Phentermine is used for short-term weight control while topiramate is prescribed to treat epilepsy and migraines. As both these drugs are known to affect the food intake and sensation of satiety, these can have an additive effect when used together in lower doses. This study examines the effectiveness and safety of these two drugs.


  • Participants enrolled in this study were 18-70 years old, with body mass index (BMI) of 27-45 kg/m2. These participants suffered from obesity-associated ailments and were on medication for some or all of the disorders.
  • Out of 2,487 patients, 994 were given placebo; 498 patients were given a daily dose of phentermine 7·5 mg and topiramate 46·0 mg, and 995 patients were given phentermine 15.0 mg and topiramate 92.0 mg, for 56 weeks.
  • “Assessment of patients included bodyweight, blood pressure, heart rate, waist circumference, clinical and laboratory variables, concomitant drugs, adverse events, and treatment compliance.”
  • Changes in bodyweight, BP, cholesterol, and blood sugar levels were measured at regular intervals and statistically analyzed.


  • Groups with phentermine and topiramate doses lost an average body weight of 8.1 kg and 10.2 kg respectively, and the placebo group lost an average body weight of 1.4 kg.
  • Risk factors (blood pressure and cholesterol) were found to have reduced in patients with obesity-related ailments; hence, antihypertensive drugs were withdrawn in many patients.
  • Patients with diabetes showed greater weight loss and lower sugar levels after drug treatment and fewer patients with prediabetics progressed to type 2 diabetes.
  • Adverse events (constipation, increased heart rate etc.) were mild and often seen across the three treatment groups. The risk of kidney stones, low blood potassium, and psychiatric ailments mildly increased in drug-treated groups, in a dose-dependent manner.

Shortcomings/Next steps
One of the limitations of this study was that endpoint assessments were not obtained for 31% of the sample. This study was also confined to an upper limit restriction of BMI of 45 kg/m2; thus, excluding more serious cases of obesity. Also, most participants in this study were white women; so the results were not generalized to other ethnicities. Stronger counseling and interventions were not tested together with both doses of the controlled formulation of phentermine plus topiramate; such a validation should be done.

The study strongly suggests the positive effects of the combination of two drugs, phentermine and topiramate, in the treatment of obesity-related disorders. The weight loss was found to be robust, as it was maintained for the 56 weeks of the study. This weight-loss treatment also resulted in a reduction in medication, and drug withdrawal in many patients. The drug treatment was particularly useful for prediabetics, as it prevented progression of the disease effectively. This study recommends the pharmacological (drug) intervention of phentermine plus topiramate, as it helps increase the success of weight-loss programs in collaboration with diet and lifestyle changes.

For More Information:
Effects of Low-dose of the Drugs Phentermine and Topiramate Together on Weight and Associated Ailments in Obese Adults: A Drug Trial
Publication Journal: Lancet, April 2011
By Kishore Gadde; David Allison
From the Duke University Medical Center, Durham, NC

*FYI Living Lab Reports Are Summaries of the Original Research.


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