Short answer: Both are approved for long-term weight management with diet and activity in adults and children 12 and older with obesity, and adults with overweight plus a weight-related condition.12 Qsymia (phentermine and topiramate) is a capsule each morning. Wegovy (semaglutide) is a weekly injection or a daily tablet and also has heart and liver uses. Only Wegovy has a boxed warning. Neither label reports a trial against the other.
| Qsymia | Wegovy | |
|---|---|---|
| What it is | Phentermine plus extended-release topiramate; phentermine is Schedule IV1 | Semaglutide, a GLP-1 receptor agonist2 |
| Form | Capsule once daily in the morning; evening doses avoided1 | Injection once a week, or tablet once daily (tablets for adults)2 |
| Dose steps | 3.75/23 mg for 14 days, then 7.5/46 mg; may go to 11.25/69 mg for 14 days, then 15/92 mg1 | Injection: 0.25 mg, rising every 4 weeks to 1.7 mg, then 1.7 or 2.4 mg; up to 7.2 mg for adult weight loss2 |
| Other approved uses | None; the label says its effect on heart disease and death has not been established1 | Lowering major heart event risk in adults with heart disease and obesity or overweight; MASH with moderate to advanced liver fibrosis in adults (injection)2 |
| Side effects in adult trials | At 15/92 mg: tingling 20% vs 2% on placebo, dry mouth 19% vs 3%, constipation 16% vs 6%1 | At 2.4 mg: nausea 44% vs 16% on placebo, diarrhea 30% vs 16%, vomiting 24% vs 6%2 |
| Pregnancy | Can cause birth defects; monthly pregnancy tests recommended; sold only through certified pharmacies (REMS)1 | Stopped at least 2 months before a planned pregnancy2 |
| Boxed warning | None1 | Thyroid C-cell tumors2 |
The Qsymia warnings come mostly from topiramate: suicidal thoughts, sudden nearsightedness with a form of glaucoma, mood and sleep problems, trouble with concentration and memory, metabolic acidosis, kidney stones, and seizures if stopped suddenly, so the 15/92 mg dose is tapered every other day for at least a week.1 The Wegovy warnings include pancreatitis, gallstones (1.6% vs 0.7% on placebo with the injection), low blood sugar with insulin or a sulfonylurea, kidney injury from fluid loss and food in the lungs during anesthesia.2 Both labels say they can raise resting heart rate.12 These numbers come from separate trials with different people, lengths and methods, so they are not a head-to-head comparison.
Which, if either, fits is for your prescriber. More detail: Qsymia side effects, Wegovy side effects, the Qsymia and Wegovy dosing schedules, the Qsymia and Wegovy missed-dose pages, Contrave vs Qsymia: how do the two weight-loss pills compare? and Xenical vs Wegovy: what do the labels show?.