phentermine and topiramate extended-release

What is phentermine and topiramate, and how does it work (mechanism of action)?

  • Qsymia is a combination product that contains phentermine and topiramate in an extended release form. It helps some obese (body mass index [BMI] = 30 km/m2) adults or some overweight (BMI = 27 km/m2) adults with weight-related medical problems lose weight and keep the weight off.
  • Phentermine is a sympathomimetic agent that has been used by itself for the treatment of obesity for quite some time. Although the exact mechanism by which phentermine works to promote weight loss is not understood, it is thought to stimulate the release of chemicals from the hypothalamus, the area of the brain known to have a major role in regulating hunger and food intake. Phentermine induced release of chemicals is thought to reduce appetite and decrease food intake, among other effects.
  • Topiramate, the other medicine in Qsymia, is an anti-seizure medication that has been observed to be effective in causing weight loss. The precise mechanism by which topiramate works to stimulate weight loss is not yet understood. However, similar to the actions of phentermine, topiramate is also thought to suppress appetite and make a person feel full even after eating less food than usual.
  • The effectiveness of Qsymia was proven by two placebo-controlled clinical studies. At the end of 1 year of treatment patients had an average weight loss of 7.8% compared to 1.2 to 1.6% for placebo treated patients. Furthermore, approximately 62 to 70% of patients lost = 5% of their body weight compared to about 17 to 21% of patients who received placebo.
  • Qsymia was approved by the FDA in July 2012. Use and distribution of Qsymia is under stricter control by the federal government because it contains phentermine, a medicine that has a high potential for abuse and drug dependence. As such, Qsymia is classified as a schedule IV controlled substance.

What brand names are available for phentermine and topiramate?


Is phentermine and topiramate available as a generic drug?


Do I need a prescription for phentermine and topiramate?


What are the uses for phentermine and topiramate?

  • Qsymia is an oral weight loss medicine that may help some obese adults (body mass index [BMI] = 30 km/m2) or some overweight adults (BMI = 27 km/m2) with weight-related medical problems such as high blood pressure, type 2 diabetes, or dyslipidemia lose weight and keep the weight off. To achieve maximum weight loss, Qsymia should be used with a reduced calorie diet and increased physical activity.
  • The safety and effectiveness of Qsymia with other prescription, over-the-counter (OTC), or herbal weight loss medications has not been established. Therefore, use of Qsymia with such agents is not recommended.
  • The safety and effectiveness of Qsymia has not been established in pediatric patients. Therefore, use of Qsymia in pediatrics is not recommended.


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What are the side effects of phentermine and topiramate?

The most common side effects of Qsymia are:

Rare, but serious side effects associated with Qsymia therapy include mood changes, trouble sleeping, problems with concentration or memory, speech difficulties, an increase in acid levels in the blood, low blood sugar especially in patients with type 2 diabetes mellitus who are also taking medicines to treat their blood sugar, seizures, kidney stones, decreased sweating, and fever.

What is the dosage for phentermine and topiramate?

  • The starting dose of Qsymia is 3.75/23 mg capsule by mouth once each morning for the first 14 days. Thereafter, the recommended dose is one Qsymia 7.5/46 mg capsule once each morning for 12 weeks. If weight loss of at least 3% of body weight does not occur, discontinue or the dose may be increased to one Qsymia 11.25/69 mg capsule once each morning for 14 days. Thereafter, take one Qsymia 15/92 mg capsule once each morning.
  • Stop taking Qsymia if at least 5% weight loss is not achieved after an additional 12 weeks of treatment on the higher dose.
  • To stop Qsymia, patients should take a dose (determined by your doctor) every other day for at least 1 week and then before stopping stop treatment altogether. Stopping Qsymia suddenly can cause serious medical problems such as seizures. Individuals should inform their doctor before stopping the medication.
  • Patients with moderate (creatinine clearance 30 to <50 ml/min) to severe kidney disease (creatinine clearance <30 ml/min) should not exceed Qsymia dose of 7.5/46 mg per day.
  • For patients with liver disease, do not exceed Qsymia 7.5/46 mg per day in patients with moderate (Child-Pugh Score= 7 to 9) liver disease.
  • Although clinical trials are ongoing, the drug is not yet approved for use in the pediatric population.

Which drugs or supplements interact with phentermine and topiramate?

  • Qsymia should not be used during or within 14 days of treatment with a monoamine oxidase inhibitor (MAOIs), due to the risk of hypertensive crisis, a condition in which blood pressure becomes dangerously high and can cause organ damage or death.
  • Qsymia can alter blood concentrations of certain birth control medicines. This may cause irregular bleeding, but does not seem to increase the risk of pregnancy. Patients are advised not to discontinue their birth control pills if spotting occurs. Instead, patients should speak to their doctor or pharmacist if the spotting is troubling to them.
  • Taking Qsymia with alcohol or other CNS depressant drugs (for example, barbiturates, benzodiazepines or anti-anxiety agents, and sleep medications) increases the risk of drowsiness, confusion, loss of coordination, and other central nervous system (CNS) depression symptoms.
  • Taking Qsymia with certain water pills (diuretics) such as hydrochlorothiazide (HCTZ) may cause a decrease in the level of potassium in the blood (hypokalemia).
  • Qsymia decreases blood levels of carbamazepine (Tegretol) and valproic acid (Depakote).
  • Administration of topiramate, a component of Qsymia, with carbonic anhydrase inhibitors (for example, zonisamide [Zonegran], acetazolamide [Diamox]) may increase the levels of acid in the blood which consequently may increase the risk of kidney stone formation. Co-administration of such agents is not recommended.

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Is phentermine and topiramate safe to take if I'm pregnant or breastfeeding?

  • Qsymia may cause birth defects and should not be used during pregnancy. Use of topiramate, a component of Qsymia, during pregnancy has been associated with an increased risk of oral clefts. For this reason Qsymia has been classified as FDA pregnancy risk category X, and a program called Qsymia REMS was developed to help prevent fetal exposure to Qsymia. Patients, prescribers, and pharmacies must be registered in the Qsymia REMS programs to receive, prescribe, and dispense Qsymia. To prevent exposure to the unborn baby, females of reproductive age must have a negative pregnancy test before starting Qsymia and monthly thereafter while on Qsymia therapy. Additionally, females of reproductive age should use effective birth control methods during Qsymia therapy.
  • Qsymia may be excreted into human milk because topiramate, a component of Qsymia, is known to enter breast milk. Due to the potential risk of causing serious side effects in the nursing infant, a decision should be made to either stop nursing or taking Qsymia.

What else should I know about phentermine and topiramate?

What preparations of phentermine and topiramate are available?

Oral capsules (phentermine mg/topiramate mg extended-release): 3.75/23 mg, 7.5/46 mg, 11.25/69 mg, and 15/92 mg.

How should I keep phentermine and topiramate stored?

  • Capsules should be stored at room temperature between 15 C to 30 C (59 F to 86 F).
  • Qsymia is a schedule IV controlled substance because it contains phentermine. Due to the high potential for abuse and drug dependence, Qsymia should be kept in a safe place to protect it from theft.


Qsymia (phentermine and topiramate extended-release) is a combination of two drugs prescribed to treat individuals who are overweight or obese, in conjunction with diet and exercise. Side effects, drug interactions, dosing, storage, and pregnancy safety information should be reviewed prior to taking this medication.

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