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Weight loss

Phentermine + Topiramate

An effective once-daily oral obesity medicine whose weight-loss benefit must be balanced against pregnancy, cognitive, mood, and cardiovascular precautions.

Strong
Evidence rating
Evidence review

What the evidence says

Extended-release phentermine/topiramate combines a sympathomimetic appetite suppressant with an antiseizure medicine and is approved for chronic weight management in eligible patients. Dose escalation and response checkpoints are built into treatment, and high-dose therapy must be tapered rather than abruptly stopped.[3]

In the 56-week CONQUER trial, average weight change was approximately -7.8% with the mid dose and -9.8% with the high dose, versus -1.2% with placebo. Two-year SEQUEL follow-up found sustained average losses near 9% to 10% among continuing participants.[1][2]

Comparative meta-analysis places phentermine/topiramate among the most effective oral obesity medicines, although trial dropout and differing populations complicate rankings. A digitally delivered lifestyle trial also found additional loss when structured behavioral treatment accompanied medication.[5][4]

Topiramate exposure in pregnancy increases oral-cleft and fetal-growth risks, so pregnancy testing and effective contraception are required for people who can become pregnant. Paresthesia, dry mouth, constipation, insomnia, increased heart rate, mood symptoms, cognitive difficulty, metabolic acidosis, kidney stones, and eye emergencies also shape selection and monitoring.[3]

Potential benefits

  • Produces roughly 8% to 10% average weight loss at effective doses over one year in trial populations.[1]
  • Weight and several cardiometabolic improvements can persist through two years with continued treatment.[2]

Side effects and cautions

  • Paresthesia, dry mouth, constipation, insomnia, attention or memory problems, and heart-rate increase are common practical limitations.[3]
  • It can cause fetal harm, mood or suicidal symptoms, metabolic acidosis, kidney stones, and acute angle-closure glaucoma; abrupt high-dose withdrawal can provoke seizures.[3]
How we scored it

Evidence breakdown

Two large phase 3 programs show substantial one- and two-year weight loss, supported by comparative meta-analysis and detailed regulatory safety controls.

Clinical relevanceHigh

Trials measure weight loss, cardiometabolic markers, adverse events, and two-year durability.

Study qualityHigh

Evidence includes large randomized placebo-controlled trials and extension follow-up.

Safety dataHigh

A boxed fetal-toxicity warning and a formal risk-management program define key safeguards.

References

Full source list

  1. Effects of low-dose, controlled-release, phentermine plus topiramate combination on weight and associated comorbidities

    The Lancet · 2011

  2. Two-year sustained weight loss and metabolic benefits with controlled-release phentermine/topiramate

    American Journal of Clinical Nutrition · 2012

  3. Qsymia (phentermine and topiramate extended-release) prescribing information

    DailyMed, U.S. National Library of Medicine · 2025

  4. Digital lifestyle intervention with phentermine-topiramate for obesity: a randomized clinical trial

    Obesity · 2026

  5. Association of pharmacological treatments for obesity with weight loss and adverse events

    JAMA · 2016