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Phentermine / topiramate Side Effects

In Summary

Commonly reported side effects of phentermine/topiramate include: constipation, insomnia, nasopharyngitis, paresthesia, mood disorder, sleep disorder, and xerostomia. Other side effects include: urinary tract infection, anxiety, blurred vision, depression, dizziness, fatigue, influenza, nausea, increased serum creatinine, and dysgeusia. See below for a comprehensive list of adverse effects.

For the Consumer

Applies to phentermine / topiramate: oral capsule extended release

Along with its needed effects, phentermine/topiramate may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking phentermine / topiramate:

Less common
  • Chest discomfort
  • convulsions
  • decreased urine
  • fast, irregular, pounding, or racing heartbeat or pulse
  • loss of appetite
  • mood changes
  • muscle pain or cramps
  • nausea or vomiting
  • numbness or tingling in the hands, feet, or lips
  • shortness of breath
  • unusual tiredness or weakness
  • Blood in the urine
  • pain in the groin or genitals
  • sharp back pain just below the ribs
Incidence not known
  • Blistering, peeling, or loosening of the skin
  • blisters on the mouth, trunk, scalp, or other areas
  • blurred or decreased vision
  • chest pain
  • chills or shivering
  • clumsiness
  • continuing nausea or vomiting
  • cough or sore throat
  • dark urine
  • diarrhea or light-colored stools
  • dizziness
  • headache
  • increase in the frequency of seizures
  • irregular heartbeat
  • itching
  • joint or muscle pain
  • loss of appetite
  • low body temperature
  • muscle aches or weakness
  • pain in the shoulders, arms, jaw, or neck
  • red skin lesions, often with a purple center
  • red, irritated eyes
  • shakiness in the legs, arms, hands, or feet
  • sores, ulcers, or white spots in the mouth or on the lips
  • sweating
  • swelling of the face
  • tiredness and weakness
  • trouble thinking, speaking, or walking
  • upper right abdominal or stomach pain
  • weak or feeble pulse
  • weight gain
  • yellow eyes or skin

Some side effects of phentermine / topiramate may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

More common
  • Back pain
  • change in taste
  • difficulty having a bowel movement (stool)
  • ear congestion
  • fear or nervousness
  • loss of taste
  • loss of voice
  • memory problems
  • pain or tenderness around the eyes and cheekbones
  • sneezing
  • stuffy or runny nose
  • trouble sleeping
Less common Incidence not known
  • Bloating
  • false or unusual sense of well-being
  • feeling that others are watching you or controlling your behavior
  • feeling that others can hear your thoughts
  • feeling, seeing, or hearing things that are not there
  • hives or welts
  • change in sexual ability, desire, drive, or performance
  • severe mood or mental changes
  • unusual behavior

For Healthcare Professionals

Applies to phentermine / topiramate: oral capsule extended release

Nervous system

Very common (10% or more): Paraesthesia (up to 19.9%), headache (up to 10.6%)
Common (1% to 10%): Dysgeusia, dizziness, hypoesthesia, disturbance in attention, cognitive impairment

Postmarketing reports: Euphoria, psychosis, tremor[Ref]


Common (1% to 10%): Insomnia, anxiety, depression/mood problems, irritability
Postmarketing reports: Suicidal ideation, suicidal behavior

Postmarketing reports: Libido changes, impotence[Ref]


Very common (10% or more): Decreased serum bicarbonate (up to 12.8%)
Common (1% to 10%): Hypokalemia, decreased serum potassium, decreased appetite

Postmarketing reports: Hyperammonemia[Ref]


Common (1% to 10%): Elevated serum creatinine, nephrolithiasis[Ref]


Very common (10% or more): Elevated resting heart rate (up to 77.7%)
Common (1% to 10%): Palpitations

Postmarketing reports: Elevated blood pressure, ischemic events[Ref]


Common (1% to 10%): Blurred vision, dry eye, eye pain
Postmarketing reports: Acute angle closure glaucoma, increased intraocular pressure

Postmarketing reports: Maculopathy[Ref]


Common (1% to 10%): Fatigue, thirst, chest discomfort, procedural pain

Postmarketing reports: Hypothermia[Ref]


Common adverse reactions occurring at a rate of 5% or more and at a rate of at least 1.5 times placebo include paraesthesia, dizziness, dysgeusia, insomnia, constipation, and dry mouth.[Ref]


Common (1% to 10%): Alopecia, rash

Postmarketing reports: Bullous skin reactions (including erythema multiforme, Stevens-Johnson syndrome, toxic epidermal necrolysis), pemphigus[Ref]


Very common (10% or more): Dry mouth (up to 19.1%), constipation (up to 16.1%)
Common (1% to 10%): Nausea, diarrhea, gastroesophageal reflux disease, dyspepsia, oral paraesthesia, gastroenteritis

Postmarketing reports: Pancreatitis[Ref]


Common (1% to 10%): Dysmenorrhea, urinary tract infection[Ref]


Postmarketing reports: Hepatic failure (including fatalities), hepatitis[Ref]


Postmarketing reports: Urticaria[Ref]


Common (1% to 10%): Influenza[Ref]


Common (1% to 10%): Back pain, extremity pain, muscle spasms, musculoskeletal pain, neck pain[Ref]


Very common (10% or more): Upper respiratory tract infection (up to 15.8%), nasopharyngitis (up to 12.5%)
Common (1% to 10%): Sinusitis, bronchitis, cough, sinus congestion, pharyngolaryngeal pain, nasal congestion[Ref]


1. "Product Information. Qsymia (phentermine-topiramate)." Vivus Inc, Mountain View, CA.

Some side effects of phentermine / topiramate may not be reported. Always consult your doctor or healthcare specialist for medical advice. You may also report side effects to the FDA.

Disclaimer: Every effort has been made to ensure that the information provided is accurate, up-to-date and complete, but no guarantee is made to that effect. In addition, the drug information contained herein may be time sensitive and should not be utilized as a reference resource beyond the date hereof. This material does not endorse drugs, diagnose patients, or recommend therapy. This information is a reference resource designed as supplement to, and not a substitute for, the expertise, skill , knowledge, and judgement of healthcare practitioners in patient care. The absence of a warning for a given drug or combination thereof in no way should be construed to indicate safety, effectiveness, or appropriateness for any given patient. does not assume any responsibility for any aspect of healthcare administered with the aid of materials provided. The information contained herein is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. If you have questions about the substances you are taking, check with your doctor, nurse, or pharmacist.