|This article's listed sources may not meet Wikipedia's guidelines for reliable sources. (June 2012)|
|Phentermine||Appetite suppressant/stimulant of the amphetamine and phenethylamine class|
|Pregnancy cat.||X (US)|
|Legal status||Schedule IV (US) Approved by the FDA on July 17, 2012|
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The combination of the drugs phentermine and topiramate (trade name Qsymia, formerly Qnexa) is a medication for the treatment of obesity and potentially related conditions such as type 2 diabetes and has been found to lower blood pressure and cholesterol.  Qsymia was developed by Vivus, a California pharmaceutical company. Phentermine is an appetite suppressant and stimulant of the amphetamine and phenethylamine class. Topiramate is an anticonvulsant that has weight loss side effects.
On February 22, 2012, U.S. Food and Drug Administration (FDA) advisors voted 20 to 2 to recommend that the FDA adopt phentermine/topiramate as an obesity treatment. Final approval was expected later in 2012, with recommendations for post-market monitoring for cardiovascular risk and an indication against use by pregnant women. On July 17, 2012, the U.S. FDA approved Qsymia as an addition to a reduced-calorie diet and exercise for chronic weight management. It is currently available only through specialty mail-order pharmacies.
Safety and effectiveness 
Clinical studies have shown weight loss under treatment with Qnexa. The phase 3, 56-week EQUIP study showed that the average weight loss of 14.7% (37 lbs) was achieved by obese patients treated with Qnexa. The following doses of phentermine IR and topiramate CR were used in Phase 3 testing:
- Full strength formula: 15 mg of phentermine IR (instant-release) and 92 mg of topiramate CR (controlled-release)
- Mid strength formula: 7.5 mg phentermine IR and 46 mg topiramate CR
- Low strength formula: 3.75 mg phentermine IR and 23 mg topiramate CR
In 2009, Vivus reported that the main side effects during testing phases were dry mouth, a tingling in the fingers and toes and constipation. However, in 2010 Public Citizen's Dr. Sidney M. Wolfe testified before the FDA Advisory Committee that studies showed that Qnexa carries a long list of relatively rare but potentially serious side effects, including possible birth defects
Studies and timeline 
EQUIP investigated the combination for 56 weeks in severely obese patients.
A 108-week trial rolling-over patients from CONQUER, collecting long-term data.
Approval history 
FDA approval was declined in October 2010 due to concerns about dangerous side effects, including suicidal thoughts, heart palpitations, memory lapses and birth defects.
In January 2011, the FDA expressed concerns about the potential for Qnexa to cause birth defects and asked Vivus to examine this possibility before the drug can be approved.
Patents and other indications 
Vivus currently has four U.S. patents covering Qnexa. These patents are related to the product and methods of using the drug in various therapeutic applications.
Qnexa is also in phase 2 clinical development for the treatment of type 2 diabetes and obstructive sleep apnea (OSA). A phase 2 safety and efficacy study evaluating Qnexa in patients with OSA showed that patients who took Qnexa had a 69 percent reduction in sleep apnea events and lost more weight than those who took placebo.
Further research data released indicates that Qnexa lowers blood pressure. Dr. Suzanne Oparil of the University of Alabama at Birmingham stated “The higher the dose, the more weight loss and the more blood pressure went down” presented at the American Society of Hypertension’s 25th annual meeting in New York. Her co-authored study was subsequently accepted and published by the American Journal of Cardiology.
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- Weight Loss Drug Too Dangerous to Be Allowed On Market
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- Effects of low-dose, controlled-release, phentermine plus topiramate combination on weight and associated comorbidities in overweight and obese adults (CONQUER)., 
- Two-year sustained weight loss and metabolic beneﬁts with controlled-release phentermine/topiramate in obese and overweight adults (SEQUEL), 
- VIVUS Submits Qnexa(R) New Drug Application to the FDA for the Treatment of Obesity
- FDA accepts Vivus application for obesity drug
- "FDA rejects second weight-loss drug in a week". msnbc.com news services. 10/29/2010 5:06:32 AM ET. Retrieved 29 October 2010.
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- Hellmich, Nancy. "New diet drug helps patients lose about 10% of weight". USA Today. Retrieved 17 July 2012.
- "Medications Target Long-Term Weight Control". FDA.gov. Retrieved 17 July 2012.
- VIVUS Announces the Issuances of Three Additional Qnexa(R) Patents
- Vivus' Qnexa improves sleep apnea in small trial
- Qnexa weight loss drug lowers blood pressure: study
- Changes in Cardiovascular Risk Associated With Phentermine and Topiramate Extended-Release in Participants With Comorbidities and a Body Mass Index ≥27 kg/m2