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Qsymia (phentermine/topiramate ER): Weight Loss Drug Side Effects & Dosage

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
  • 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,
    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.

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.

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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,
    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

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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
  • 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.

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