Qsymia is an FDA-approved once-daily prescription pill that combines phentermine and extended-release topiramate to produce about 8 to 10 percent body weight loss at one year. It is approved for adults with a BMI of 30 or higher, or 27 or higher with a weight-related condition. Side effects include dry mouth, tingling, constipation, mood changes, and altered taste; topiramate makes it unsafe in pregnancy.
What Qsymia Is
Qsymia (pronounced kew-SIM-ee-uh) is a single capsule combining two well-established medications:
- Phentermine — a sympathomimetic that releases norepinephrine in the brain, reducing appetite. Phentermine has been used for weight loss since 1959.
- Topiramate extended-release — an anticonvulsant and migraine preventive that independently reduces appetite, increases satiety, and may reduce reward-driven eating.
The FDA approved Qsymia in July 2012 for chronic weight management. It is manufactured by Vivus (now part of Currax Pharmaceuticals) and is one of only a handful of oral anti-obesity drugs with chronic-use labeling.
Who Qualifies
The FDA-approved indication is for use alongside reduced calorie diet and increased physical activity in adults who meet one of these criteria:
- BMI of 30 kg/m² or higher (obesity)
- BMI of 27 kg/m² or higher (overweight) plus at least one weight-related comorbidity — hypertension, dyslipidemia, type 2 diabetes, sleep apnea, or cardiovascular disease
Qsymia is also approved for children 12 to 17 years old with obesity (BMI in the 95th percentile or higher for age and sex), following 2022 FDA action expanding the label.
How It Works
The two components act through different mechanisms that complement each other:
- Phentermine increases norepinephrine release in hypothalamic appetite centers, reducing hunger.
- Topiramate modulates GABA, glutamate, and voltage-gated sodium channels — the exact appetite mechanism is uncertain but likely includes reduced food reward, slowed gastric emptying, and an altered taste of sweet foods.
Because of the dual action, lower doses of each ingredient produce greater weight loss than either alone, with somewhat fewer side effects than higher monotherapy doses.
Dosing Schedule
Qsymia comes in four fixed-dose combinations. Treatment starts low and titrates up.
| Step | Dose (phentermine/topiramate) | Duration | Purpose |
|---|---|---|---|
| Start | 3.75 mg / 23 mg | 14 days | Tolerance check |
| Standard | 7.5 mg / 46 mg | 12 weeks | Primary maintenance dose |
| Step-up | 11.25 mg / 69 mg | 14 days | If <3% weight loss at 12 weeks |
| Top | 15 mg / 92 mg | Ongoing | Maximum dose |
If a patient has not lost at least 3 percent of body weight after 12 weeks on the standard dose, the prescriber should either escalate to the top dose or discontinue Qsymia. If 5 percent loss is not reached at 12 weeks on the top dose, the medication should be stopped — non-responders are unlikely to benefit from continued treatment.
Qsymia is taken once daily in the morning. Evening dosing increases insomnia risk because phentermine is stimulating.
Expected Weight Loss
Two pivotal trials established Qsymia’s efficacy.
| Trial | Population | Dose | Mean Weight Loss at 1 Year | ≥10% Loss |
|---|---|---|---|---|
| EQUIP | BMI ≥35, no diabetes | 15/92 mg | 10.9% | 47% |
| EQUIP | Same | Placebo | 1.6% | 7% |
| CONQUER | BMI 27-45 + comorbidities | 15/92 mg | 9.8% | 48% |
| CONQUER | Same | 7.5/46 mg | 7.8% | 37% |
| CONQUER | Same | Placebo | 1.2% | 7% |
The 2-year SEQUEL extension showed continued benefit: patients who stayed on Qsymia 15/92 maintained 9.3 percent weight loss at 108 weeks. Improvements in blood pressure, lipids, fasting glucose, and waist circumference paralleled the weight loss.
Common Side Effects
The most frequent adverse effects in clinical trials, at the top dose, were:
- Paresthesia (tingling, especially hands and feet) — 21%
- Dry mouth — 19%
- Constipation — 16%
- Dysgeusia (altered taste, particularly carbonated beverages) — 9%
- Insomnia — 9%
- Dizziness — 9%
- Mood changes including anxiety, irritability, depression — 4 to 6%
- Cognitive slowing, word-finding difficulty, impaired concentration — 6%
Most side effects are dose-dependent and improve over the first 4 to 8 weeks.
Serious Risks
- Teratogenicity — topiramate increases the risk of oral cleft (cleft lip or palate) in babies exposed in the first trimester. Qsymia is contraindicated in pregnancy. Female patients of reproductive potential must use effective contraception and have a negative pregnancy test before starting and monthly during treatment.
- Elevated heart rate — modest rise of 1.6 beats per minute on average; not recommended in those with recent cardiovascular events.
- Suicidal ideation — topiramate carries a class warning for antiepileptic drugs.
- Metabolic acidosis — topiramate inhibits carbonic anhydrase, lowering serum bicarbonate. Periodic monitoring is recommended.
- Kidney stones — calcium phosphate stones from the same mechanism; staying well hydrated reduces risk.
- Acute angle-closure glaucoma — rare but vision-threatening; immediate eye care if eye pain or vision change.
- Hypoglycemia — when used alongside insulin or sulfonylureas, dose adjustments to those medications may be needed.
Contraindications
- Pregnancy
- Glaucoma
- Hyperthyroidism
- Use of monoamine oxidase inhibitors (MAOIs) within 14 days
- Known hypersensitivity to sympathomimetic amines
Caution is needed in patients with recent myocardial infarction, unstable angina, uncontrolled hypertension, severe kidney or liver disease, and history of suicidal ideation.
How Qsymia Compares
| Medication | Class | Average Weight Loss (1 yr) | Route |
|---|---|---|---|
| Qsymia | Phentermine + topiramate | ~8-10% | Oral, once daily |
| Contrave | Naltrexone + bupropion | ~5-9% | Oral, twice daily |
| Phentermine alone | Sympathomimetic | ~5-8% | Oral, daily |
| Orlistat | Lipase inhibitor | ~3-4% | Oral, with meals |
| Wegovy (semaglutide) | GLP-1 receptor agonist | ~15% | Weekly injection |
| Zepbound (tirzepatide) | GIP/GLP-1 dual | ~21% | Weekly injection |
Qsymia is the most effective oral pill currently approved for weight loss, but newer injectable GLP-1-based therapies generally produce larger weight reductions.
Cost and Access
Qsymia is brand-name only — no generic exists. Cash price runs about $200 per month, though Vivus offers a direct-to-consumer program at roughly $98 per month and a savings card for commercially insured patients. Many insurance plans cover it with prior authorization documenting BMI and a comorbidity. Medicare Part D historically excludes anti-obesity drugs, though policy may change.
Practical Considerations
- Take in the morning to avoid insomnia.
- Drink plenty of water — helps constipation, kidney stone risk, and metabolic acidosis.
- Expect altered taste of carbonated drinks; often resolves or becomes tolerable.
- Avoid abrupt discontinuation — taper to reduce seizure risk from topiramate withdrawal.
- Combine with diet, exercise, and behavioral support — medication alone underperforms its trial numbers.
- Reassess at 12 weeks: if not 3 percent down on the standard dose or 5 percent on the top dose, stop.
Related Reading
For broader context, see our anti-obesity medications overview, our guides on Contrave and phentermine, and our pillar on treatment options for type 2 diabetes and prediabetes.
The Bottom Line
Qsymia is a once-daily oral combination of phentermine and topiramate that produces 8 to 10 percent body weight loss at one year — the most effective oral anti-obesity pill currently available. It is approved for adults with BMI 30 or higher, or 27 or higher with a weight-related condition. Common side effects are dry mouth, tingling, altered taste, constipation, insomnia, and cognitive or mood changes. Pregnancy is the major absolute contraindication because of topiramate teratogenicity. Talk to your doctor about whether Qsymia fits your medical history and goals, and combine it with sustained lifestyle change for the best long-term results.
