Short answer: Both are approved for long-term weight management with diet and activity in adults with obesity, or overweight plus a weight-related condition, and in children 12 and older with obesity.12 Saxenda (liraglutide) is a daily injection stepped up to 3 mg. Qsymia (phentermine and topiramate) is a capsule each morning stepped up from 3.75/23 mg. Only Saxenda has a boxed warning. Neither label reports a trial against the other.
| Saxenda | Qsymia | |
|---|---|---|
| What it is | Liraglutide, a GLP-1 receptor agonist1 | Phentermine plus extended-release topiramate; phentermine is Schedule IV2 |
| Children | 12 and older with obesity and body weight over 60 kg1 | 12 and older with obesity2 |
| How taken | Injection under the skin once a day, any time of day1 | Capsule once daily in the morning2 |
| Dose steps | 0.6 mg in week 1, rising 0.6 mg each week to 3 mg from week 51 | 3.75/23 mg for 14 days, then 7.5/46 mg; may go to 15/92 mg by way of 11.25/69 mg2 |
| When adults stop | Less than 4% of starting weight lost at 16 weeks, or 3 mg not tolerated1 | Less than 5% lost after 12 weeks on 15/92 mg, tapering over at least a week2 |
| Side effects in adult trials | Nausea 39.3% vs 13.8% on placebo, diarrhea 20.9% vs 9.9%, constipation 19.4% vs 8.5%1 | At 15/92 mg: tingling 20% vs 2% on placebo, dry mouth 19% vs 3%, constipation 16% vs 6%2 |
| Boxed warning | Thyroid C-cell tumors1 | None2 |
Saxenda's warnings include pancreatitis, gallstones (2.2% vs 0.8% on placebo), low blood sugar in people with type 2 diabetes on a sulfonylurea or insulin, kidney injury from fluid loss and food in the lungs during anesthesia.1 Qsymia's include birth defects, with sales only through certified pharmacies, suicidal thoughts, sudden nearsightedness with a form of glaucoma, mood and sleep problems, metabolic acidosis, kidney stones and seizures if stopped suddenly.2 Both labels say resting heart rate can rise.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: Saxenda side effects, Qsymia side effects, the Saxenda and Qsymia dosing schedules, the Saxenda and Qsymia missed-dose pages, and Saxenda vs Wegovy: how do the two weight-loss injections differ?.