Phentermine / Topiramate ER — Clinical Evidence
All published trials referenced on this site. Click any source link to read the original journal article.
Last reviewed: March 2026
Randomised controlled trials
In the following trials, participants were randomly assigned to Phentermine / Topiramate ER or a dummy pill (placebo). All weight loss figures are average body weight reductions from baseline.
| Trial | Key result | Source |
|---|---|---|
| [1]CONQUER | 9.8% weight loss at 15/92 mg (full dose) vs. 1.2% placebo. 70% achieved ≥5% loss. Significant blood pressure, triglyceride, and glucose improvements. | The Lancet 2011 ↗ |
| [2]SEQUEL (2-year extension of CONQUER) | Sustained weight loss with continued metabolic improvements at 2 years, confirming durability of effect. | American Journal of Clinical Nutrition 2012 ↗ |
Reported side effects
Frequencies from CONQUER. View source ↗
| Side effect | Frequency in trial |
|---|---|
| Paraesthesia (tingling in hands/feet) | 20% |
| Dry mouth | 21% |
| Constipation | 17% |
| Insomnia | 10% |
| Dizziness | 9% |
| Cognitive effects ('brain fog') | 8% |
Body composition data
No large published body composition substudy is available for phentermine/topiramate specifically. As a primarily appetite-suppressing drug without the metabolic effects of GLP-1 agonists, lean mass preservation depends heavily on protein intake and resistance training during the calorie deficit.
Cardiovascular & metabolic data
In CONQUER, significant reductions in blood pressure, waist circumference, triglycerides, and blood glucose were observed. However, phentermine raises heart rate — careful monitoring is required in people with cardiovascular disease.