Topiramate lowers weight in some people, and its label treats that as a side effect. The anti-seizure and migraine drug sold as Topamax has never carried a US weight indication. Its obesity trials of the early 2000s found real weight loss, and none of them led to an approval. This page reports what the label and those trials record, dated, and where the record stops.
Read on 10 November 2026 from the Topamax label (Janssen, DailyMed set 21628112, revised March 2026), Drugs@FDA, and the trials cited below.
What the label is for
Topamax was first approved on 24 December 1996 (NDA 020505, Drugs@FDA). Its current label covers two uses: epilepsy (on its own or added to other seizure drugs, from age 2) and the preventive treatment of migraine from age 12. The label contains no weight-management claim.
The same molecule, in an extended-release form, is one half of Qsymia, the long-term weight medicine approved in July 2012. That is a different label, with different trials and lower topiramate strengths.
What the label's tables record
The label reports weight in its adverse-reaction tables, as the share of people who reported weight loss:
| Trial set (label table) | Placebo | Topiramate |
|---|---|---|
| Adult migraine prevention, pooled (Table 8) | 1% (n=445) | 6% on 50 mg/day (n=235) · 9% on 100 mg/day (n=386) |
| Adult add-on epilepsy, pooled (Table 6) | 3% (n=291) | 9% on 200–400 mg/day (n=183) |
| Epilepsy monotherapy, adults, low vs high dose (Table 5) | — | 6% on 50 mg/day (n=160) · 17% on 400 mg/day (n=159) |
The same tables list anorexia (loss of appetite) beside it: 6% on placebo against 9% and 15% on the two migraine doses. In children, the label warns separately about negative effects on growth, height and weight, from a one-year study.
What these figures are not. They are the share of people who reported weight loss as a side effect, not mean weight changes, and the trials were not designed to measure weight. They show that the effect is common and rises with dose; they do not show how much weight is lost.
What the obesity trials of topiramate alone measured
Between 2003 and 2007 the drug's sponsor ran trials of topiramate in people with obesity. Each one paired the drug with a lifestyle programme, and each compared it with placebo:
| Trial | Population | Length | Topiramate arms | Placebo |
|---|---|---|---|---|
| Bray et al., Obes Res 2003 | 385 adults with obesity | 24 weeks | −5.0% to −6.3% (four doses, 64–384 mg/day) | −2.6% |
| Wilding et al., Int J Obes 2004 (OBES-002) | 1,289 enrolled, 854 analysed; BMI 30–50, or 27–50 with controlled blood pressure or lipids | 60 weeks | −7.0%, −9.1%, −9.7% (96, 192, 256 mg/day) | −1.7% |
| Astrup et al., Obes Res 2004 | 701 started an 8-week low-calorie diet; those who lost ≥8% were randomised; 293 analysed | 44 weeks | −15.4%, −16.5% of starting weight (diet loss included) | −8.9% |
| Rosenstock et al., Diabetes Care 2007 | 111 adults with type 2 diabetes, BMI ≥27 | 16 weeks | −5.8% (controlled-release, up to 175 mg/day) | −2.3% |
In the largest trial, 54% to 67% of the topiramate groups lost at least 5% of body weight, against 18% on placebo.
Two limits matter more than the numbers. First, the two long trials did not run to the end: in both, the sponsor stopped the study early to develop a new controlled-release formulation, so the figures come from the people who reached the one-year or 44-week point before the stop. Second, the side effects drove dropouts. In the 2003 trial, 21% on topiramate left because of side effects, against 11% on placebo. A 2011 meta-analysis of 10 trials and 3,320 people put the extra loss at 5.34 kg over placebo, with the odds of stopping for a side effect 1.94 times higher.
The authors of the 2007 trial, the one that tested the controlled-release version, wrote that its nervous-system and psychiatric side-effect profile "makes it unsuitable for the treatment of obesity and diabetes." No topiramate-alone weight approval appears in the FDA record.
Where the approved weight data sit
The approved long-term weight data for topiramate are in Qsymia, which pairs extended-release topiramate with phentermine at strengths from 23 mg up to 92 mg of topiramate per capsule. That is below the doses the obesity trials above tested, and the combination exists because it did better than either drug alone: in a 28-week trial, 48.6% lost at least 5% on topiramate 92 mg alone, against 66.0% on the combination. The Qsymia page sets out its one-year trials and its pregnancy safety programme. Those figures belong to the combination, not to topiramate alone.
For a sense of scale, with the populations named: in their own one-year trials of adults with obesity and no diabetes, semaglutide 2.4 mg gave −14.9% against −2.4% on placebo over 68 weeks (STEP 1), and tirzepatide 15 mg gave −20.9% against −3.1% over 72 weeks (SURMOUNT-1). No trial compares any of these with topiramate directly, and the trials differ in era, length and how dropouts were counted. The full list of non-GLP-1 options is on GLP-1 alternatives.
Safety the label prints
The Topamax label's warnings section includes, among others:
- Eye problems — acute myopia and secondary angle-closure glaucoma, and visual field defects.
- Metabolic acidosis — a fall in blood bicarbonate from loss through the kidney; the label recommends measuring it at the start and periodically.
- Cognitive and psychiatric effects — confusion, slowed thinking, difficulty concentrating, memory and word-finding problems, and mood effects; plus the class warning on suicidal thoughts that applies to seizure drugs.
- Pregnancy — use in pregnancy can cause major birth defects, including cleft lip and palate, and being small for gestational age.
- Kidney stones — 1.5% of adults in the add-on epilepsy trials, about two to four times the expected rate.
- Reduced sweating and raised body temperature, especially in children, and high ammonia with brain effects in some people.
Those are the label's warnings as printed, not a full list. They are the reason the drug is prescribed and monitored, and any question about its use for weight belongs with the prescribing clinician.
What is not established
- No regulator has approved topiramate alone for weight, so no label gives a weight endpoint for it.
- The long obesity trials were stopped early by their sponsor; no completed multi-year trial of topiramate alone in obesity has been published.
- The trials are from 2003–2007 and did not measure the outcomes later weight-drug trials report, such as heart events.
- Whether a lower dose taken off-label for weight would match the trial figures is not something those trials tested.
This is where a reader should stop and ask a clinician — whether a seizure and migraine medicine with these warnings is suitable at all, and how it compares with an approved weight medicine for one person, is a medical decision this page does not and cannot make.
Sources
- TOPAMAX (topiramate) prescribing information, Janssen Pharmaceuticals, revised March 2026 — DailyMed, read 10 November 2026: sections 1, 5, 6 (Tables 5, 6, 8).
- Drugs@FDA, NDA 020505 (Topamax), original approval 24 December 1996.
- Bray GA et al., Obesity Research 2003, PMID 12805393. Wilding J et al., International Journal of Obesity 2004, PMID 15486569. Astrup A et al., Obesity Research 2004, PMID 15536230. Rosenstock J et al., Diabetes Care 2007, PMID 17363756. Kramer CK et al., Obesity Reviews 2011, PMID 21438989. Aronne LJ et al., Obesity 2013, PMID 24136928.
- Wilding JPH et al., NEJM 2021, PMID 33567185 (STEP 1). Jastreboff AM et al., NEJM 2022, PMID 35658024 (SURMOUNT-1).