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.