Phentermine and topiramate
A once-daily capsule combining phentermine, an appetite suppressant, with topiramate, an anticonvulsant. Qsymia is the FDA-approved brand.
Brand names: Qsymia
Phentermine and topiramate (known as Qsymia)
Also searched as: phentermine topiramate extended-release.
Educational information. This page does not give dosing instructions or tell you what to take. Ask a prescriber about your own care.
In plain English
Qsymia puts two older medicines in one capsule. Phentermine is a stimulant-type appetite suppressant. Topiramate is a seizure and migraine medicine that, at the doses used here, also lowers appetite. Neither acts on GLP-1.
In the main 56-week trial (CONQUER), adults lost about 8% of their body weight on the lower dose and about 10% on the higher dose, versus about 1% on placebo. That is less than the newer weekly injections, but it is a pill.
Qsymia has one unusual restriction. Topiramate can cause birth defects, so the FDA requires a pregnancy-risk program (REMS), and only certified pharmacies can dispense it. It is approved for adults and for teens 12 and older with obesity.
Brand names and products
A generic name identifies the drug itself. A brand name identifies one company's product. One drug can come in several products with different forms and approved uses, so the brand name often tells you more about what a prescription is for.
| Brand name | Maker | Form | U.S. approved use | Status |
|---|---|---|---|---|
| Qsymia | VIVUS LLC | Daily capsule | Weight management | FDA-approved for weight management |
Approved and investigational. Each product above is approved only for the use shown. Qsymia is FDA-approved for chronic weight management. That approval covers this product and its labeled uses only, not every use of phentermine or topiramate.
How it works
Phentermine is a sympathomimetic amine, a drug related to amphetamines that raises the release of the brain chemical norepinephrine and dampens appetite. How topiramate lowers appetite is not fully understood. Qsymia combines the two in an extended-release capsule so that smaller amounts of each are used.
Forms and approval status
| Form | How it is taken | U.S. status |
|---|---|---|
| Phentermine and topiramate extended-release capsules (Qsymia) | Once daily. Daily capsule. Follow the label and your prescriber. It is not for use in pregnancy, and pregnancy tests are recommended before starting and monthly during treatment. | Approved in the U.S. as an add-on to a reduced-calorie diet and more physical activity, to reduce excess weight and keep it off. For adults with obesity, adults with overweight plus a weight-related condition, and patients 12 and older with obesity. It is a Schedule IV controlled substance and is dispensed only through certified pharmacies under a pregnancy-risk program (REMS). |
What the trials found
These are group averages from published trials in adults without diabetes unless stated. See how to read trial numbers before comparing.
CONQUER
Average change in body weight. Every bar uses one scale, 0 to 25 percent.
- People studied
- 2,487 adults with overweight or obesity (BMI 27 to 45) and at least two weight-related conditions
- Length
- 56 weeks
- Compared with
- Placebo, with office-based lifestyle advice in all groups
- What was measured
- Average change in body weight at week 56
- Analysis approach
- Intention-to-treat, as reported in the abstract
- Other results
- Weight loss of at least 5%: 62% (lower dose) and 70% (higher dose) vs 21% with placebo. At least 10%: 37% and 48% vs 7%.
- Safety
- Most common: dry mouth (13% and 21% vs 2% on placebo), tingling or numbness (14% and 21% vs 2%), constipation, insomnia, dizziness and taste changes. Depression-related events: 4% and 7% vs 4%. Anxiety-related events: 5% and 8% vs 3%.
- Limits
- Funded by the manufacturer. Participants were U.S. adults aged 18 to 70, so results may not match other groups. Group averages do not predict one person's result.
Sources: Gadde KM 2011
Safety
Based on the FDA-approved label for Qsymia. The official label is the controlling source for warnings. The points below are a summary and may be incomplete.
Boxed warning and label notes
- Phentermine and topiramate extended-release capsules (Qsymia): No boxed warning. Contraindicated in pregnancy, glaucoma, hyperthyroidism and with or within 14 days of an MAOI antidepressant.
Warnings labels describe
- Birth defects: topiramate in early pregnancy is linked to oral clefts and smaller babies. Pregnancy tests and effective contraception are advised, and a REMS program limits dispensing to certified pharmacies.
- Can raise suicidal thoughts (an anticonvulsant class warning), cause eye problems including acute angle-closure glaucoma, and affect mood, sleep, memory and attention.
- Can cause metabolic acidosis, kidney stones, higher heart rate and, if stopped abruptly at the highest strength, seizures.
- Effect on heart attack and stroke risk has not been established.
Most common in trials
- Tingling or numbness (paresthesia)
- Dry mouth
- Constipation
- Taste changes
- Insomnia
- Dizziness
Less common but serious
- Birth defects if taken during pregnancy
- Suicidal thoughts or behavior
- Acute myopia with angle-closure glaucoma
- Metabolic acidosis
- Kidney stones
- Severe allergic or skin reactions
What is still unknown
- Whether it lowers the risk of heart attacks and strokes. The label says this has not been established.
- How weight changes after stopping, and how well results hold beyond a year or two.
- How it compares directly with the GLP-1 medicines. No head-to-head trial is recorded in this atlas, and indirect comparisons are weaker evidence.
Compiled from public information: FDA-approved labels, manufacturer websites, ClinicalTrials.gov and published journal articles. Sources are listed at the bottom of this page.
Sources
- Qsymia (phentermine and topiramate extended-release) capsules: prescribing information VIVUS LLC, on DailyMed (U.S. National Library of Medicine). FDA-approved label, April 2026 listing. Official FDA label on DailyMed
- DailyMed: current FDA drug labels U.S. National Library of Medicine. Regulator
- Drugs@FDA: approved drug products U.S. Food and Drug Administration. Regulator
- Effects of low-dose, controlled-release, phentermine plus topiramate combination on weight and associated comorbidities in overweight and obese adults (CONQUER) Gadde KM, et al. Lancet. 2011;377(9774):1341-1352. PMID 21481449. Funding: Vivus. Journal article