Skip to main content

How Does Qsymia work for weight loss?

Medically reviewed by Leigh Ann Anderson, PharmD. Last updated on May 12, 2025.

Official Answer by Drugs.com

Qsymia is a combination of two drugs, phentermine and extended-released topiramate and works in two ways: phentermine acts to lower the appetite and reduce food intake and topiramate can help you feel more full.

Phentermine is classified as a sympathomimetic amine, central nervous system stimulant and appetite suppressant (anorexiant) and and acts on the brain to suppress your appetite. Topiramate is an anticonvulsant (seizure medicine) used to treat epilepsy and for migraine headache prevention.

The exact mechanism of action of Qsymia is not fully known.

Learn more: Weight Loss and Diet Pills: What are My Options?

Who can use Qsymia?

Qsymia (phentermine and topiramate ER) is used for chronic weight management in:

The manufacturer provides a BMI chart using patient height and weight in the product label. It is manufactured by Vivus Pharmaceuticals and was first approved in 2012.

The Qsymia dose is taken once daily in morning with or without food; you should avoid an evening dose as it may interfere with sleep.

Your doctor will slowly increase your dose over a 28-day period and will evaluate your weight loss after 12 to 24 weeks of treatment with Qsymia, depending upon your final dose.

Related questions

How well does Qsymia work for weight loss?

In 56-week long clinical trials, patients lost on average 14.5 kg (32 lb) using Qsymia 15 / 92 mg plus diet and exercise, and about 5 inches off of their waist. Patients using a placebo (an inactive pill with no medicine) lost 2.7 kg (6 lb) and 1.7 inches.

Related: Does topiramate cause weight loss?

Is Qsymia a controlled substance?

This is not all the information you need to know about Qsymia (phentermine and topiramate ER) for safe and effective use and does not take the place of your doctor’s directions. Review the full product information and discuss this information and any questions you have with your doctor or other health care provider.

References

Read next

Zepbound Vs Mounjaro: Complete Comparison Guide for Weight Loss and Diabetes Treatment

Comprehensive comparison of Zepbound vs Mounjaro. Learn about their uses, dosing, effectiveness, costs, and safety profiles to understand which medication might be right for you. Continue reading

Ozempic Side Effects to Watch For

The most common Ozempic side effects with Ozempic include stomach problems, like nausea, vomiting, diarrhea, stomach pain and constipation. These tend to be mild-to-moderate and usually clear up in a few weeks in most people. Low blood sugar (hypoglycemia) is also a common side effect (when used with certain other diabetes treatments) and it can be serious. Continue reading

Why am I not losing weight on Mounjaro?

It takes time, about 8 to 12 weeks to see a 6% to 8% weight loss in adults using Mounjaro. Other reasons include the need to follow a reduced calorie diet and exercise program, your dose may need to be increased, or side effects may affect your treatment. Continue reading

See also:

Related medical questions

Drug information

Related support groups