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With over 2/3 of the U.S. adult population overweight or obese, there is an urgent need for efficacious interventions, including medications. Historically, medications to facilitate weight loss have not been very successful; virtually all weight loss medications initially approved by the FDA have been withdrawn, overtaken by severe and sometimes fatal complications.

Qsymia is the most recent attempt to have an effective medication whose benefits outweigh the risks.

What is Qsymia?

Qsymia is a combination of two existing medications:

  • Phentermine – an appetite suppressant that has been around for over 50 years. It is approved by the FDA for short-term (3 months) use in the management of obesity.
  • Topirimate – a medication currently on the market for the last 16 years that is used to treat seizures and migraines.

Qsymia combines these medications in various dosages (see clinical results below). Qsymia results in weight loss in most adults.

Mechanism of Action of Qsymia

It is believed that multiple mechanisms of action result in weight loss with this combination of medications. These include:

  • Decreased hunger
  • Increased satiety (“fullness”)
  • Increased metabolic rate (“burning more calories”)
  • Decreased binge eating episodes
  • Alterations in taste perception, affecting food reward

Clinical Results

The Qsymia combination of Phentermine and Topirimate has been studied with three different dosages:

  • Qsymia-Low (dose): Phentermine 3.75 mg / Topirimate 23 mg
  • Qsymia-Medium (dose): Phentermine 7.5 mg / Topirimate 46 mg
  • Qsymia-High (dose): Phentermine 15 mg / Topirimate 92 mg

Some studies have included the effects on weight utilizing the individual components (phentermine and topirimate). These are abbreviated and included in the analysis:

  • PTM–Medium (dose): Phentermine 7.5 mg
  • PTM–High (dose): Phentermine 15 mg
  • TPM–Med (dose): Topirimate 46 mg
  • TPM–High (dose): Topirimate 92 mg

Percent Initial Body Weight Loss


28 Weeks

56 Weeks

108 weeks

Placebo (control)



1.8 %

Qsymia -L





























  • "-" indicates study was not performed
  • Maximum approved doses of the individual components are:
    • Phentermine: 37.5 mg/day
    • Topirimate: 400 mg/day

Adverse Effects of Qsymia

Significant possible side effects from the two components fall into three broad categories:

Nervous System

  • Anxiety
  • Depression
  • Insomnia
  • “Tingling” (Paraesthesia)
  • Cognitive/memory impairment
  • Visual impairment/glaucoma

Metabolic abnormalities

  • Acidosis (build-up of acid in the body)
  • Kidney stones
  • Osteoporosis

Cardiovascular Complications

  • Hypertension
  • Increased heart rate
  • Cardiac arrhythmias (irregular heart beats)
  • Chest pain/angina/myocardial infarct (“heart attack”)
  • Dissection of coronary arteries (“tearing” of the artery), especially post-pregnancy
  • Stroke

Special Concerns with Qsymia - BIRTH DEFECTS

Topirimate is a known to cause birth defects thus, it is CRITICAL that women of childbearing age avoid pregnancy. This is especially important since fertility generally increases in overweight and obese women with weight reduction.

Possible Significant Medication Interactions

Metformin (brand name Glucophage), a medication for diabetes, probably should not be used with Qsymia since a significant acidosis (build-up of acid in the body) may occur.

Medications that function as stimulants such as some asthma/allergy medications and tricyclic antidepressants (such as imipramine) should generally be avoided to minimize cardiovascular adverse events such as rapid heart beats or elevated blood pressure..

What Happens when you discontinue Qsymia?

Once treatment with the medication is stopped, weight generally returns to pre-treatment or higher levels.


Qsymia can assist appropriately selected individuals in reducing body weight while the medication is used. Care must be exercised in individuals with cardiovascular disease or who are taking prescription and non-prescription medications.

Extreme care by women of childbearing age must be undertaken to prevent pregnancy and the subsequent risk of significant birth defects while using Qsymia.

Updated: 27 December 2011

Copyright © 1996 -2011 Michael D. Myers, M.D., Inc.
All rights reserved.

Disclaimer Statement

The above information is for general purposes only and should not be construed as definitive or binding medical advice, diagnosis or treatment. Because each person is medically different, individuals should consult their own personal physicians for specific information and/or treatment recommendations.