Qsymia: what it treats, how to take it, side effects
Last updated September 3, 2026.
Qsymia is a once-daily prescription capsule combining phentermine (an appetite suppressant) and topiramate extended-release (an anti-seizure drug that also reduces appetite). It is the most effective of the traditional weight-loss pills, and it comes with a REMS restricted-distribution program because topiramate causes birth defects.
What does it treat?
Chronic weight management, with diet and activity changes, in adults with obesity or overweight with a related condition, and in pediatric patients 12 and older with obesity. The two ingredients attack appetite from two angles: phentermine suppresses hunger short-term, topiramate extends the effect and adds satiety.
How do you take it?
Once each morning, with or without food, starting at the lowest strength (3.75/23 mg) for 14 days, then the standard 7.5/46 mg, with possible escalation to 15/92 mg for inadequate response. Morning dosing matters because phentermine causes insomnia if taken late. Never stop the top dose abruptly: it is tapered every other day for at least a week to avoid triggering seizures. Weight is checked at 12 weeks on each dose level, and non-response means discontinuation. Because of birth-defect risk, people who can become pregnant need a negative pregnancy test before starting and monthly during treatment, plus effective contraception, under the Qsymia REMS program.
Side effects to know
- Common: tingling in hands, feet, or face (paresthesia), dizziness, metallic or altered taste, insomnia, constipation, and dry mouth.
- Serious: fetal harm (cleft lip and palate), suicidal thoughts and behavior, acute myopia and secondary angle-closure glaucoma (eye pain and vision change are stop-immediately symptoms), mood and sleep problems, attention and memory difficulty, increased heart rate, kidney stones, metabolic acidosis, slowed growth in children, and serious skin and allergic reactions.
Who should not take it?
Not in pregnancy (the REMS exists because of it), not with glaucoma or hyperthyroidism, not within 14 days of an MAO inhibitor, and not with known hypersensitivity to sympathomimetics. Heart disease, uncontrolled hypertension, and a history of drug abuse all weigh against the phentermine side. Kidney or liver impairment caps the dose. Oral contraceptives still work on it, but unusual spotting can occur. It is a Schedule IV controlled substance.
When is it an emergency?
Call 911 for sudden eye pain with vision changes, a seizure, severe allergic reaction (swelling, trouble breathing), or a spreading blistering rash. Thoughts of self-harm mean call or text 988 (US) and contact your prescriber. Symptoms like severe fatigue with rapid breathing can signal metabolic acidosis and need same-day care. Pymander's escalation routing is built and tested specifically for this class of decision; see the safety architecture working paper.
What a Pymander AI doctor consult looks like
Illustrative example, not a real member's messages.
Common questions
How much weight do people lose on Qsymia?
The most of any traditional pill: roughly 9 to 11% of body weight over a year at the higher doses in trials, versus a couple percent on placebo. That is why the checkpoints exist at each dose level: if a dose is not producing, the response is to reassess, not to keep climbing forever.
Why does it need a special program and monthly pregnancy tests?
Topiramate roughly doubles the risk of cleft lip and palate in first-trimester exposure, so the FDA required the Qsymia REMS program: the drug ships through certified pharmacies, and people who can become pregnant test before starting and monthly during treatment, with effective contraception throughout. It is administrative friction with a real reason.
Why can't I just stop taking it?
Topiramate is an anti-seizure drug, and stopping any such drug abruptly can provoke seizures, even in people without epilepsy. The label tapers the top dose every other day for at least a week before stopping. Any discontinuation, planned or because you ran out, follows that rule.
What is the tingling about?
Paresthesia, tingling or pins-and-needles in hands, feet, or face, is the single most common Qsymia effect, from topiramate's carbonic-anhydrase activity. It is annoying but benign, often easing over weeks. The same mechanism is behind the metallic taste, kidney stones (hydrate well), and the metabolic acidosis monitoring.
Is Qsymia addictive?
It is Schedule IV because of the phentermine, putting it in the low-but-real abuse-potential class, like the benzodiazepines. At prescribed doses, dependence is mostly a story of abrupt-stop seizure risk from the topiramate rather than craving, but a history of substance abuse is part of the screening conversation.
How does it compare to the GLP-1 injections?
Qsymia is the strongest oral option (about 9 to 11% average loss), while semaglutide and tirzepatide injections average higher still. Qsymia's advantages are being a pill, being generic-adjacent in cost terms compared with the injectables, and decades of phentermine experience; the injectables win on average efficacy and on cardiovascular-outcome data. It is a legitimate lane, not a consolation prize.