Phentermine / topiramate Side Effects

It is possible that some side effects of phentermine / topiramate may not have been reported. These can be reported to the FDA here. Always consult a healthcare professional for medical advice.

For the Consumer

Applies to phentermine / topiramate: oral capsule extended release

As well as its needed effects, phentermine / topiramate may cause unwanted side effects that require medical attention.

If any of the following side effects occur while taking phentermine / topiramate, check with your doctor immediately:

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 phentermine / topiramate side effects may not need any medical attention. As your body gets used to the medicine these side effects may disappear. Your health care professional may be able to help you prevent or reduce these side effects, but do check with them if any of the following side effects continue, or if you are concerned 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
  • Belching
  • cramps
  • decreased appetite
  • dry eyes
  • eye pain
  • hair loss
  • heartburn or indigestion
  • heavy bleeding
  • irritability
  • rash
  • stomach discomfort, upset, or pain
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


Cardiovascular side effects have included palpitations (up to 2.4%) and chest discomfort (up to 2.1%).[Ref]


Dermatologic side effects have included rash (up to 2.6%) and alopecia (up to 3.7%).[Ref]


Gastrointestinal side effects have included constipation (up to 16.1%), dry mouth (up to 19.1%), nausea (up to 7.2%), dyspepsia (up to 2.8%), gastroesophageal reflux disease (up to 2.6%), gastroenteritis (up to 2.5%), decreased appetite (up to 2.1%), paresthesia oral (up to 2.2%), and thirst (up to 2%).[Ref]


Genitourinary side effects have included urinary tract infection (up to 5.2%) and dysmenorrhea (up to 2.1%).[Ref]


Hepatic side effects have included nephrolithiasis (up to 1.2%).[Ref]


Immunologic side effects have included influenza (up to 6.7%).[Ref]


Metabolic side effects have included hypokalemia (up to 2.5%), decreased serum bicarbonate (up to 8.8%), decreased serum potassium (up to 4.9%) and decreased serum creatinine (up to 2.5%).[Ref]


Musculoskeletal side effects have included and back pain (up to 6.6%), pain in extremity (up to 3%), muscle spasms (up to 2.9%), musculoskeletal pain (up to 3%), and neck pain (up to 2.2%).[Ref]

Nervous system

Nervous system side effects have included paresthesia (up to 19.9%), headache (up to 10.6%), dizziness (up to 8.6%), dysgeusia (up to 9.4%), fatigue (up to 5.9%), irritability (up to 3.7%), hypoesthesia (up to 3.7%), and disturbance in attention (up to 3.5%).[Ref]


Ocular side effects have included blurred vision (up to 6.3%), eye pain (up to 2.2%), and dry eye (up to 2.5%).[Ref]


Other side effects of phentermine reported postmarketing have included allergic reactions, urticaria, cardiovascular adverse reactions, elevation of blood pressure, ischemic events, central nervous system adverse reactions, euphoria, psychosis, tremor, reproductive adverse reactions, changes in libido, and impotence. Other side effects of topiramate reported postmarketing have included dermatologic disorders, bullous skin reactions (including erythema multiforme, Stevens-Johnson syndrome, toxic epidermal necrolysis), pemphigus, gastrointestinal disorders, pancreatitis, hepatic disorders, hepatic failure (including fatalities), hepatitis, metabolic disorders, hyperammonemia, hypothermia, ophthalmic disorders, and maculopathy.[Ref]


Psychiatric side effects have included insomnia (up to 9.4%), depression (up to 4.3%), and anxiety (up to 4.1%).[Ref]


Respiratory side effects have included upper respiratory tract infection (up to 15.8%), nasopharyngitis (up to 12.5%), sinusitis (up to 7.8%), bronchitis (up to 6.7%), cough (up to 4.8%), sinus congestion (up to 2.6%), pharyngolaryngeal pain (up to 2.5%), and nasal congestion (up to 2%).[Ref]


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

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.