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
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:
- Paraesthesia (sensations of pricking, burning, tingling, or numbness of
- Blurred vision
- Urinary tract infections
- Back pain
- Taste disturbances
Insomnia or trouble sleeping
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)
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,
anti-anxiety agents, and
increases the risk of drowsiness,
confusion, loss of coordination, and other
central nervous system (CNS)
- Taking Qsymia with certain water pills (diuretics) such as
hydrochlorothiazide (HCTZ) may cause a decrease in the level of potassium in the
- Qsymia decreases blood levels of
carbamazepine (Tegretol) and
valproic acid (Depakote).
- Administration of topiramate, a component of Qsymia, with carbonic anhydrase
inhibitors (for example,
acetazolamide [Diamox]) may
increase the levels of acid in the blood which consequently may increase the
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?
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.