Qsymia combines low-dose phentermine (an appetite-suppressing sympathomimetic) with extended-release topiramate (which adds a central appetite effect). Together they produce more weight loss than either alone — moderate on average, but less than the GLP-1 drugs. It is taken as a once-daily oral capsule and is contraindicated in pregnancy and glaucoma.
Obesity Medication Library entry. Section accent: family --teal.
DRUG FACT PANEL
| Generic | Phentermine / topiramate extended-release |
| Brand | Qsymia |
| Class | Fixed combination: sympathomimetic (phentermine) + neurostabiliser (topiramate ER) |
| Mechanism (1 line) | Phentermine suppresses appetite via noradrenaline release; topiramate adds a complementary central appetite effect |
| FDA indication | Chronic weight management in adults (and eligible adolescents) with obesity, or overweight with a weight-related condition |
| Who it's for | Adults wanting an oral chronic-management option; not for people who can become pregnant without reliable contraception, or with glaucoma/hyperthyroidism |
| Route/formulation | Oral capsule, once daily (fixed dose combinations) |
| Titration concept | Started at a low combined dose and stepped up over weeks; tapered when stopping — individual dosing is set by a clinician, not this page |
| Expected effect | Moderate — top-dose trials (CONQUER/EQUIP, ~1 year, with lifestyle) show roughly ~9–10% total body-weight loss; below the GLP-1/dual-agonist agents on average, but above the other older oral drugs |
| Evidence level (obesity) | Grade A 🟢 — RCTs (CONQUER, EQUIP, SEQUEL) + guideline support |
What Qsymia is
Qsymia is a fixed-dose oral combination of two older drugs used at lower, complementary doses: phentermine, a short-term appetite suppressant, and extended-release topiramate, an anticonvulsant/migraine drug with an appetite-suppressing effect. Pairing them lets each be used at a lower dose while their effects add up — and, unlike phentermine alone, the combination is approved for chronic (long-term) weight management, not just short-term use. → Phentermine · Topiramate
How it works
The two components work through different appetite pathways:
- Phentermine stimulates central noradrenaline release, reducing hunger.
- Topiramate adds a central appetite-suppressing effect through its several CNS mechanisms.
Because the pathways differ, the combination produces greater average weight loss than either drug on its own, at lower individual doses than each would need alone. Neither engages the incretin biology of the GLP-1 drugs, which is part of why the combination sits below them on efficacy. → Why Weight Is So Hard to Lose
What the trials actually show
Qsymia's approval rests on randomised trials (the CONQUER, EQUIP and SEQUEL program) showing clinically meaningful weight loss over roughly a year, greater than placebo and greater than either component alone. At the top dose, those trials (CONQUER and EQUIP, over roughly a year, alongside lifestyle change) showed on the order of ~9–10% total body-weight loss — clearly above placebo. In the broad efficacy ranking of approved drugs, Qsymia lands in a moderate tier — better on average than orlistat or naltrexone/bupropion, but below semaglutide and tirzepatide. As always, that figure is a trial average, not a personal prediction. → Semaglutide · Tirzepatide
Side effects
Common: tingling (paresthesia, from topiramate), dry mouth, constipation, altered taste, insomnia, dizziness, and cognitive effects (word-finding difficulty, slowed thinking). Increased heart rate and elevated blood pressure can occur (from phentermine).
Less common / serious: meaningful blood-pressure or heart-rate elevation, acute angle-closure glaucoma, kidney stones and metabolic acidosis (topiramate), mood changes, and teratogenicity. The combination carries the cautions of both components. → Topiramate · Phentermine
Contraindications & cautions
- Pregnancy — contraindicated; topiramate is teratogenic (oral clefts). Reliable contraception is required in those who can become pregnant, with pregnancy testing before and during use. → Women's Health & Obesity
- Glaucoma — contraindicated (acute angle-closure risk from topiramate).
- Hyperthyroidism — contraindicated (phentermine).
- Recent/concurrent MAO inhibitors — contraindicated (hypertensive-crisis risk).
- Cardiovascular disease / uncontrolled hypertension — caution or avoid (phentermine's sympathomimetic effect). → Obesity & Cardiovascular Health
Monitoring, pregnancy and surgery
- Monitoring: blood pressure and heart rate; mood, sleep and cognition; hydration and kidney-stone symptoms; pregnancy testing where relevant; eye symptoms warrant urgent attention.
- Pregnancy/lactation: contraindicated in pregnancy; effective contraception is essential and the drug is stopped if pregnancy is planned or confirmed. This is a defining caution for Qsymia. → Women's Health & Obesity
- Perioperative: disclose use to the surgical/anaesthesia team (sympathomimetic and metabolic-acidosis considerations).
Long-term considerations, discontinuation and weight regain
Qsymia is approved for chronic management, and its benefit depends on continued use — stopping is typically followed by regain, as with every effective obesity drug. Because of the topiramate component, it should be tapered rather than stopped abruptly. Maintenance should be planned before starting. For patients who need greater efficacy, or who have contraindications to either component, an incretin agent may be more appropriate — a clinical decision, not a default. → Weight Regain & Maintenance
Unanswered questions
- Head-to-head durability versus the incretin drugs.
- Long-term cardiovascular safety of the phentermine component in chronic use.
- Best sequencing when incretins are unavailable, not tolerated, or declined.
Questions patients ask
How does Qsymia work?
It combines low-dose phentermine (which suppresses appetite via noradrenaline) with extended-release topiramate (a complementary central appetite effect). Together they work better than either alone. Grade A 🟢
Is Qsymia as effective as Wegovy or Zepbound?
No — on average it produces moderate weight loss, meaningfully below the GLP-1 drugs, though above orlistat and Contrave. It remains a useful oral option. Grade A 🟢 → Semaglutide
Can I take Qsymia if I might get pregnant?
Only with reliable contraception — it's contraindicated in pregnancy because topiramate is teratogenic (cleft lip/palate). Pregnancy testing is done before and during use. Grade A 🟢 → Women's Health & Obesity
Why can't people with glaucoma take it?
The topiramate component can trigger acute angle-closure glaucoma, so it's contraindicated in glaucoma. Any new eye pain or vision change needs urgent attention. Grade A 🟢
Will it raise my blood pressure?
It can — the phentermine component can raise heart rate and blood pressure, so it's cautioned or avoided in cardiovascular disease and uncontrolled hypertension. Grade B 🟡 → Obesity & Cardiovascular Health
Will I regain weight if I stop?
Usually yes — it treats a chronic disease, so stopping is typically followed by regain. It should also be tapered, not stopped abruptly. Grade A 🟢 → Weight Regain & Maintenance
KEEP READING
- Obesity Medication Library — where Qsymia ranks among all approved options.
- Phentermine and Topiramate — the two components, individually.
- Semaglutide and Tirzepatide — the higher-efficacy incretin tier.
- Women's Health & Obesity — contraception and pregnancy cautions.
Written by Darius A. Schneider, MD, PhD · Board-Certified Endocrinologist (ECNU) · Last updated: 2026-08-10 · References: Qsymia FDA prescribing information; CONQUER, EQUIP, SEQUEL trials; obesity pharmacotherapy guidelines. Not individualized medical advice.
