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Phentermine / topiramate Side Effects

Medically reviewed by Last updated on Aug 28, 2022.


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. Continue reading for a comprehensive list of adverse effects.

Applies to phentermine / topiramate: oral capsule extended release.

Serious side effects

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
  • decreased urine
  • dry mouth
  • 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
  • seizures
  • trouble breathing
  • 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

Other side effects

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


Frequency not reported: Oligohidrosis

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 (2012):

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.