The quick comparison
Qsymia and GLP-1 medicines are both prescription weight-management treatments meant to be combined with a reduced-calorie diet and increased physical activity. The headline difference is delivery and average effect size: Qsymia is a once-daily oral capsule that produced roughly 8%-11% average weight loss across its top two doses in year-long trials, while the leading GLP-1 injectables averaged higher (roughly 15%-21% at the top doses) in their own separate trials.
The table below summarizes the key facts. Numbers come from each drug's own pivotal trials and FDA labeling — they were not generated in a single head-to-head study, so treat the weight-loss figures as indicative of typical results in different trial populations rather than a direct one-to-one contest.
How each one works
Qsymia combines two older drugs. Phentermine is a sympathomimetic amine anorectic that reduces appetite (chemically related to amphetamine, which is why Qsymia is a Schedule IV controlled substance). Topiramate is an anti-seizure and migraine drug that, in this combination, is thought to reduce appetite and increase feelings of fullness. The two are delivered as an extended-release capsule taken once every morning (VIVUS/Qsymia prescribing information, 2024-2026).
GLP-1 medicines work on gut-hormone pathways. Semaglutide (Wegovy) mimics glucagon-like peptide-1, a hormone that slows stomach emptying and signals fullness to the brain. Tirzepatide (Zepbound) activates two receptors — GLP-1 and GIP — which is associated with the larger average weight loss seen in its trials. Both are injected under the skin once weekly (FDA labeling; NEJM STEP 1 2021 and SURMOUNT-1 2022).
Weight loss in clinical trials
Qsymia's efficacy comes from two 56-week Phase 3 trials. In EQUIP (adults with severe obesity), the top dose (phentermine 15 mg/topiramate 92 mg) produced 10.9% average weight loss vs 1.6% for placebo, with the starting dose (3.75 mg/23 mg) at 5.1% (Allison et al., EQUIP, 2012). In CONQUER (adults with overweight/obesity plus comorbidities), the top dose averaged 9.8% and the recommended 7.5 mg/46 mg dose averaged 7.8%, vs 1.2% placebo (Gadde et al., CONQUER, The Lancet, 2011). Among people who completed a full year on the drug, CONQUER weight loss was higher (about 12.4% at the top dose).
GLP-1 trials reported higher averages. In STEP 1, semaglutide 2.4 mg produced 14.9% average weight loss over 68 weeks vs 2.4% placebo (Wilding et al., NEJM, 2021). In SURMOUNT-1, tirzepatide 15 mg produced 20.9% in the intention-to-treat analysis (22.5% on-treatment) over 72 weeks; even tirzepatide's lowest 5 mg dose (~15.0%) roughly matched semaglutide 2.4 mg (Jastreboff et al., NEJM, 2022).
One honest caveat matters: no randomized trial has ever put Qsymia head-to-head against a GLP-1. The trials differ in duration, populations, doses, and eras, so the higher GLP-1 averages are a strong signal but not a controlled comparison. Individual results on any of these medicines vary widely — some people lose far more than the average and some far less.
Side effects and safety warnings
Qsymia's most common side effects in adults are paraesthesia (tingling), dizziness, altered taste (dysgeusia), insomnia, constipation, and dry mouth (Qsymia prescribing information, 2024-2026). Its labeled warnings are more extensive than a typical appetite pill: increased resting heart rate; suicidal thoughts and behavior; acute myopia and secondary angle-closure glaucoma; mood and sleep disorders; cognitive/attention and speech-language disturbances; metabolic acidosis; decreased renal function; and serious skin reactions. The 15 mg/92 mg dose must be tapered rather than stopped abruptly to reduce seizure risk.
GLP-1 side effects are predominantly gastrointestinal — nausea, diarrhea, vomiting, and constipation — usually most pronounced during dose escalation. Their labels carry a boxed warning about a risk of thyroid C-cell tumors seen in rodents (contraindicated in people with a personal/family history of medullary thyroid carcinoma or MEN 2), plus warnings about pancreatitis, gallbladder problems, and other effects (FDA labeling). The two drug classes therefore fail in different directions: Qsymia's risks skew neurologic, cardiovascular, and ophthalmologic, while GLP-1 risks skew digestive.
Any decision about starting, stopping, switching, or dosing either medication should be made with a licensed clinician who knows your full history.
Contraindications: who should not take each
Qsymia has firm contraindications. It is contraindicated in pregnancy because topiramate is teratogenic — first-trimester exposure raises the risk of oral clefts (cleft lip/palate) and small-for-gestational-age infants. It is also contraindicated in glaucoma, in hyperthyroidism, within 14 days of a monoamine oxidase inhibitor (MAOI), and in people with hypersensitivity or idiosyncrasy to sympathomimetic amines (Qsymia prescribing information; DailyMed). Because of the pregnancy risk, Qsymia is dispensed only through a restricted REMS program, and the label advises a negative pregnancy test before starting and monthly during treatment, plus effective contraception for people who can become pregnant.
GLP-1 medicines are contraindicated in people with a personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2, and in those with prior serious hypersensitivity to the drug. They are also not recommended in pregnancy. Because the contraindication lists barely overlap, someone ruled out for one class may still be a candidate for the other — which is exactly the kind of judgment a prescriber makes.
Cost and access
Both are prescription-only. Qsymia is a brand-name oral capsule; a true generic of the fixed-dose combination is not widely available, though its individual components (generic phentermine and generic topiramate) are inexpensive and are sometimes prescribed separately. Manufacturer savings programs and cash-pay pricing vary, so confirm the current price with a pharmacy or the manufacturer.
Branded GLP-1 injectables carry high list prices (often over $1,000/month before insurance or savings), but manufacturer self-pay programs have lowered cash prices substantially for people paying out of pocket. Compounded semaglutide and tirzepatide are marketed at lower prices by some telehealth providers; note that compounded GLP-1s are not FDA-approved finished drugs and are not evaluated by the FDA for safety, effectiveness, or quality the way brand products are. Insurance coverage for any weight-loss drug is inconsistent, so the real out-of-pocket number depends heavily on your plan.
We do not sell or prescribe any medication. If a GLP-1 fits what you and a clinician are considering, the offer rail on this page links to licensed telehealth providers who handle evaluation and prescribing.
Who each option may suit
Because there is no head-to-head trial and no medication is right for everyone, 'who suits which' is a clinical conversation rather than a formula. That said, some patterns follow directly from the labels. Qsymia may appeal to people who strongly prefer an oral daily pill over injections and who have none of its contraindications (not pregnant or planning pregnancy, no glaucoma, no hyperthyroidism, no recent MAOI). GLP-1 injectables may suit people seeking the largest average weight loss in trials and who can tolerate weekly injections and the GI adjustment period.
Cost, insurance coverage, side-effect tolerance, other medical conditions, and pregnancy plans all weigh into the decision. A licensed clinician will factor in your blood pressure and heart rate, mood and mental-health history, kidney function, eye health, and reproductive plans before recommending or ruling out either drug. The purpose of this page is to help you walk into that conversation informed — not to steer you toward a specific medication.