Qsymia vs GLP-1 Medications: A Head-to-Head Comparison
How does Qsymia (phentermine/topiramate ER) compare to semaglutide and tirzepatide? Evidence-based breakdown of efficacy, safety, cost, and who each medication suits best.
Medically Reviewed
Reviewed by Dr. James Chen, MD, PhD, FACE on March 23, 2026
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Introduction
Qsymia — the brand name for phentermine/topiramate extended-release (PHEN/TPM ER) — was approved by the FDA in 2012 as the first combination oral medication for chronic weight management. More than a decade later, clinicians and patients face a markedly different landscape: GLP-1 receptor agonists like semaglutide (Wegovy) and dual GIP/GLP-1 agonists like tirzepatide (Zepbound) have raised the bar considerably. Yet Qsymia remains relevant, particularly for patients who cannot afford or tolerate injectable biologics.
Evidence: In the pivotal Phase 3 CONQUER trial, full-dose Qsymia (phentermine 15 mg / topiramate 92 mg) produced a mean weight loss of 9.8% over 56 weeks compared with 1.2% for placebo. — Gadde KM, et al. Lancet. 2011. DOI: 10.1016/S0140-6736(11)60205-5
This guide synthesizes data from the major clinical trials, compares Qsymia head-to-head with newer agents, and outlines practical guidance for choosing between options.
How Qsymia Works
Qsymia combines two well-established compounds with complementary mechanisms:
- Phentermine — a norepinephrine-releasing sympathomimetic that suppresses appetite via the central nervous system. It has been used as a short-term weight-loss agent since the 1950s.
- Topiramate ER — an anticonvulsant with multiple weight-modulating effects, including modulation of GABA receptors, inhibition of carbonic anhydrase, and potential reduction in reward-related eating.
Together they reduce caloric intake more effectively than either agent alone, exploiting complementary CNS pathways. The extended-release formulation allows once-daily dosing and blunts the peak plasma concentrations that drive side effects.
Available Doses
| Dose | Phentermine | Topiramate ER | Indication |
|---|---|---|---|
| Starting | 3.75 mg | 23 mg | 2-week titration only |
| Mid | 7.5 mg | 46 mg | Target dose if 3% weight loss not achieved at 12 weeks |
| Full | 15 mg | 92 mg | Maximum dose |
Efficacy: What the Trials Show
EQUIP Trial (Severely Obese Adults)
The EQUIP trial enrolled 1,267 severely obese adults (BMI ≥35 kg/m²) and randomized them to placebo, low-dose (3.75/23 mg), or full-dose (15/92 mg) Qsymia for 56 weeks.
Evidence: Full-dose Qsymia produced 10.9% mean weight loss vs. 1.6% for placebo. The proportion achieving ≥5% weight loss was 17% (placebo) vs. 67% (full dose). — Allison DB, et al. Obesity. 2012. PubMed
CONQUER Trial (Overweight/Obese with Comorbidities)
The CONQUER trial — the largest Phase 3 study — enrolled 2,487 adults with BMI 27–45 kg/m² plus at least two obesity-related comorbidities such as hypertension, dyslipidemia, or type 2 diabetes.
| Outcome | Placebo | Mid-Dose (7.5/46) | Full-Dose (15/92) |
|---|---|---|---|
| Mean weight loss | −1.2% | −7.8% | −9.8% |
| ≥5% weight loss | 21% | 62% | 70% |
| ≥10% weight loss | 7% | 37% | 48% |
Evidence: Qsymia also improved systolic blood pressure (−1.5 to −3.0 mmHg vs. +0.2 mmHg placebo), triglycerides, and fasting insulin in the CONQUER trial. — Gadde KM, et al. Lancet. 2011. DOI: 10.1016/S0140-6736(11)60205-5
QUEEN's Study (2024 — Phase 4 Korean Adults)
A recent double-blind Phase 4 RCT in Korean adults with obesity confirmed the earlier findings in a different population:
Evidence: 68.5% of patients receiving PHEN/TPM CR achieved ≥5% weight loss vs. 25.0% on placebo at 56 weeks; mean body weight change was −8.3% vs. −2.3%. — Kim MK, et al. Obesity. 2024. PubMed
Qsymia vs. GLP-1 Receptor Agonists
Head-to-Head Efficacy Context
No direct RCT has compared Qsymia to semaglutide or tirzepatide. The comparison below uses trial-level data across similar populations and follow-up periods.
| Medication | Mechanism | Mean Weight Loss | ≥5% Responders | Route |
|---|---|---|---|---|
| Qsymia full-dose | CNS + anticonvulsant | ~10% | ~70% | Oral (daily) |
| Semaglutide 2.4 mg | GLP-1 agonist | ~13–15% | ~86% | SC injection (weekly) |
| Tirzepatide 15 mg | GIP+GLP-1 dual agonist | ~20–22% | ~91% | SC injection (weekly) |
| Placebo + lifestyle | — | ~1–2% | ~20–25% | — |
Evidence: In a head-to-head RCT (SURMOUNT-5), tirzepatide produced −20.2% weight loss vs. −13.7% for semaglutide at 72 weeks in adults with obesity without diabetes. — Jastreboff AM, et al. N Engl J Med. 2025. DOI: 10.1056/NEJMoa2416394
Qsymia's ~10% efficacy sits below injectable GLP-1 agents but meaningfully above placebo. For patients unable to use injectables — whether due to needle aversion, cost, or insurance restrictions — Qsymia offers a proven oral alternative.
Durability
Long-term data from the OB-305 extension trial showed that weight loss with Qsymia was maintained (and even slightly improved) through 2 years, with mean losses of −9.3% (mid-dose) and −10.5% (full-dose) vs. −1.8% (placebo).
GLP-1 agents show similarly durable effects during treatment, but significant weight regain occurs after discontinuation — a pattern also seen with Qsymia.
Safety and Side Effects
Common Adverse Events
The most frequently reported side effects from the CONQUER trial:
| Side Effect | Placebo | Mid-Dose | Full-Dose |
|---|---|---|---|
| Dry mouth | 2% | 13% | 21% |
| Paresthesia | 2% | 14% | 21% |
| Constipation | 6% | 15% | 17% |
| Insomnia | 5% | 6% | 10% |
| Dizziness | 3% | 7% | 10% |
| Dysgeusia | 1% | 7% | 10% |
Most side effects are dose-dependent and manageable. Paresthesia — a tingling sensation — is a known effect of topiramate and rarely leads to discontinuation.
Cognitive and Mood Effects
Attention, memory, and word-finding difficulties are reported with topiramate, particularly at higher doses. Depression and anxiety-related adverse events occurred in 7–8% of full-dose patients in CONQUER vs. 3–4% with placebo. Patients with a history of mood disorders require closer monitoring.
Cardiovascular Safety
A large pharmacoepidemiologic study found no significant increase in major adverse cardiovascular events (MACE) with phentermine/topiramate use, though confidence intervals were broad:
Evidence: Current PHEN/TPM use was not associated with a statistically significant increase in MACE risk (HR 0.84, 95% CI 0.55–1.27). — Molero Y, et al. JAMA Intern Med. 2019. PubMed
Importantly, Qsymia is contraindicated in patients with hyperthyroidism or those who have taken an MAO inhibitor within 14 days.
Teratogenicity Warning
Topiramate carries a Category D teratogenicity risk — it is associated with oral clefts and other birth defects. The FDA requires a negative pregnancy test before prescribing and monthly testing during use. Women of childbearing potential must use reliable contraception.
Who Is a Good Candidate for Qsymia?
Qsymia May Be Preferred When:
- Patient has needle aversion or refuses injectable therapy
- Cost is a major barrier — generic phentermine/topiramate is significantly less expensive than brand-name GLP-1 agents
- History of migraine headaches (topiramate is an established migraine prophylaxis)
- Patient has binge eating patterns that respond to appetite suppression
- Prior trial of lifestyle changes without adequate results
Relative Contraindications and Cautions:
- Glaucoma (topiramate raises intraocular pressure)
- Active or history of significant depression or anxiety
- Kidney stones (topiramate increases stone risk)
- Pregnancy or planning pregnancy
- Significant cardiovascular disease or uncontrolled hypertension
For a broader comparison of appetite suppressants, see Phentermine vs GLP-1 Medications and Contrave Review.
Cost and Accessibility
Qsymia brand-name pricing runs approximately $150–$250/month without insurance. However, generic phentermine and topiramate (prescribed separately as an off-label combination) can cost less than $30/month — making it one of the most affordable options for long-term weight management.
By contrast, Wegovy (semaglutide 2.4 mg) lists at over $1,300/month before insurance discounts, and Zepbound (tirzepatide) at similar levels, though manufacturer savings programs can reduce out-of-pocket costs significantly for eligible patients.
Conclusion / Key Takeaways
- Qsymia (phentermine/topiramate ER) produces approximately 10% body weight reduction at full dose over 56 weeks — confirmed in multiple Phase 3 RCTs across diverse populations.
- Newer injectable agents (semaglutide, tirzepatide) offer greater absolute weight loss (~14–22%), but at significantly higher cost and via injection.
- Qsymia has a well-characterized safety profile after more than a decade of use; the most disqualifying consideration for many patients is the teratogenicity risk from topiramate.
- For cost-sensitive, needle-averse, or migraine-prone patients, Qsymia remains a clinically meaningful and evidence-backed choice.
- Clinicians should individualize therapy based on comorbidities, contraindications, cost, and patient preference — no single agent is right for everyone.
References
Gadde KM, et al. Effects of low-dose, controlled-release, phentermine plus topiramate combination on weight and associated comorbidities in overweight and obese adults (CONQUER). Lancet. 2011;377(9774):1341–1352. DOI: 10.1016/S0140-6736(11)60205-5
Allison DB, et al. Controlled-release phentermine/topiramate in severely obese adults: a randomized controlled trial (EQUIP). Obesity. 2012;20(2):330–342. PubMed
Kim MK, et al. Evaluation of the efficacy and safety of controlled-release phentermine/topiramate in adults with obesity in Korea: A randomized, double-blind, placebo-controlled, phase 4 trial (QUEEN's study). Obesity. 2024. PubMed
Molero Y, et al. Cardiovascular Safety During and After Use of Phentermine and Topiramate. JAMA Intern Med. 2019;179(2):115–122. PubMed
Jastreboff AM, et al. Tirzepatide as Compared with Semaglutide for the Treatment of Obesity. N Engl J Med. 2025. DOI: 10.1056/NEJMoa2416394
Srivastava G, et al. Efficacy and Safety of Phentermine/Topiramate in Adults with Overweight or Obesity: A Systematic Review and Meta-Analysis. Obesity Reviews. 2021. PubMed
Last updated: 2026-03-23 Medical review: Dr. James Chen, MD, PhD, FACE
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Written By
Emily Rodriguez
Senior Medical Writer, MPH, RD
Emily Rodriguez is a registered dietitian and public health specialist. She translates complex medical research into accessible, actionable content for patients and healthcare providers.
Medical Reviewer
Dr. James Chen
Endocrinologist, MD, PhD, FACE
Dr. James Chen is a fellowship-trained endocrinologist with expertise in diabetes, metabolism, and hormone-related weight disorders. His research on GLP-1 receptor agonists has been published in leading medical journals.
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