Skip to main content

Qsymia Side Effects

Generic name: phentermine / topiramate

Medically reviewed by Drugs.com. Last updated on Dec 21, 2023.

Note: This document contains side effect information about phentermine / topiramate. Some dosage forms listed on this page may not apply to the brand name Qsymia.

Applies to phentermine / topiramate: oral capsule extended release.

Serious side effects of Qsymia

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

Rare

Incidence not known

Other side effects of Qsymia

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

Less common

Incidence not known

For Healthcare Professionals

Applies to phentermine / topiramate: oral capsule extended release.

General

The most common adverse reactions in adult patients were paresthesia, dizziness, dysgeusia, insomnia, constipation, and dry mouth. The most common adverse reactions in pediatric patients aged 12 years and older were depression, dizziness, arthralgia, pyrexia, influenza, and ligament sprain.[Ref]

Cardiovascular

In clinical trials, a higher incidence of heart rate elevations was observed with this combination drug compared to placebo. In adult patients receiving phentermine 3.75 mg-topiramate 23 mg, increased heart rate greater than 5, 10, 15, and 20 beats per minute (bpm) occurred in 70%, 50%, 32.9%, and 15% of patients, respectively. In adult patients receiving phentermine 7.5 mg-topiramate 46 mg, increased heart rate greater than 5, 10, 15, and 20 bpm occurred in 74.7%, 50.4%, 33.1%, and 13.5% of patients, respectively. In adult patients receiving phentermine 15 mg-topiramate 92 mg, increased heart rate greater than 5, 10, 15, and 20 bpm occurred in 77.7%, 56.1%, 37.3%, and 19.6% of patients, respectively. In pediatric patients receiving phentermine 7.5 mg-topiramate 46 mg, increased heart rate greater than 5, 10, 15, and 20 bpm occurred in 70.4%, 55.6%, 33.3%, and 18.5% of patients, respectively. In pediatric patients receiving phentermine 15 mg-topiramate 92 mg, increased heart rate greater than 5, 10, 15, and 20 bpm occurred in 81.4%, 64.6%, 42.5%, and 23.9% of patients, respectively.

Very common (10% or more): Increased heart rate (up to 77.7%)

Common (1% to 10%): Palpitations

Phentermine:

-Postmarketing reports: Elevated blood pressure, ischemic events

Dermatologic

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

Phentermine:

-Postmarketing reports: Urticaria

Topiramate:

-Frequency not reported: Oligohidrosis

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

Oligohidrosis (decreased sweating), infrequently resulting in hospitalization, has been associated with topiramate. Decreased sweating and elevated body temperature above normal characterized these cases. Some cases were reported with topiramate after exposure to elevated environmental temperatures.

Gastrointestinal

Very common (10% or more): Dry mouth (up to 19%), constipation (up to 16%)

Common (1% to 10%): Nausea, diarrhea, dyspepsia, gastroesophageal reflux disease, gastroenteritis, oral paresthesia

Frequency not reported: Upper abdominal pain

Topiramate:

-Postmarketing reports: Pancreatitis

Genitourinary

Common (1% to 10%): Urinary tract infection, dysmenorrhea

Phentermine:

-Postmarketing reports: Impotence

Hepatic

Topiramate:

-Postmarketing reports: Hepatic failure (including fatalities), hepatitis

Metabolic

In 1-year controlled trials of this combination drug, persistent decreases in serum bicarbonate below the normal range (levels of less than 21 mEq/L at 2 consecutive visits/at the final visit) occurred in 6.4% and 12.8% of adult patients with phentermine 7.5 mg-topiramate 46 mg and phentermine 15 mg-topiramate 92 mg, respectively. The incidence of persistent, markedly low serum bicarbonate values (levels of less than 17 mEq/L on 2 consecutive visits/at the final visit) was 0.2% for phentermine 7.5 mg-topiramate 46 mg and 0.7% for phentermine 15 mg-topiramate 92 mg. In a pediatric clinical trial, 60% to 70% of patients treated with this combination drug had a persistent bicarbonate level below the normal range (less than 21 mEq/L) compared to 43% of placebo-treated patients.

Hyperammonemia (with or without encephalopathy) has been reported with topiramate; the risk for hyperammonemia with topiramate appeared dose related and was reported more often when coadministered with valproic acid. In clinical trials of another condition, hyperammonemia occurred in 26% and 14% of pediatric patients (aged 12 to 17 years) taking topiramate 100 mg/day and 50 mg/day; an increased incidence of markedly increased hyperammonemia (50% above the upper limit of normal) also occurred at the 100 mg dose.

Very common (10% or more): Decreased serum bicarbonate (up to 12.8%)

Common (1% to 10%): Hypokalemia, decreased appetite

Uncommon (0.1% to 1%): Markedly low serum bicarbonate values

Topiramate:

-Postmarketing reports: Hyperammonemia (with or without encephalopathy), hypothermia

Musculoskeletal

This combination drug has been associated with a reduction in height velocity (cm of height gained per year) in obese pediatric patients aged 12 to 17 years. In a 56-week study, average height increased from baseline in both patients treated with this combination drug and placebo-treated patients; however, a lower height velocity of -1.3 to -1.4 cm/year was observed in patients treated with this combination drug compared to placebo-treated patients.

This combination drug was associated with less bone mineral acquisition in pediatric patients aged 12 to 17 years. In a substudy (n=66) evaluating bone mineralization via dual-energy X-ray absorptiometry (DEXA), increases in BMD at the lumbar spine and total body less head (TBLH) were smaller in pediatric patients treated with this combination drug compared to placebo-treated patients after 1 year of therapy. Declines in BMD Z-scores (standard scores) of -0.5 or greater from baseline for TBLH were observed with phentermine 7.5 mg-topiramate 46 mg (9%) and phentermine 15 mg-topiramate 92 mg (30%). The sample size and study duration were too small to determine if fracture risk was increased. Decreased BMD was not correlated with decreased serum bicarbonate (which commonly occurred with this combination drug) or changes in body weight. No patient had a BMD Z-score that went below -2 during the trial. Similar findings were observed in a 1 year, active-controlled trial of topiramate in pediatric patients with another condition.

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

Frequency not reported: Arthralgia, musculoskeletal chest pain, ligament sprain, reduced height velocity, decreased bone mineral density (BMD), reduced bone mineral acquisition

Nervous system

Very common (10% or more): Paresthesia (up to 20%), headache (up to 11%)

Common (1% to 10%): Dysgeusia, dizziness, hypoesthesia, disturbance in attention

Frequency not reported: Problems with attention/concentration, problems with memory, problems with language (word-finding)

Phentermine:

-Postmarketing reports: Tremor

In adult clinical trials, paresthesia (characterized as tingling in hands, feet, or face) and dysgeusia (characterized as a metallic taste) were reported. Paresthesia was also reported In pediatric patients.

In 1-year controlled trials of this combination drug, 5% and 7.6% of adult patients reported at least 1 cognitive-related adverse reaction with phentermine 7.5 mg-topiramate 46 mg and phentermine 15 mg-topiramate 92 mg, respectively. These adverse reactions primarily included problems with attention/concentration, memory, and language (word-finding) and occurred at any time during treatment with this combination drug.

Ocular

Common (1% to 10%): Blurred vision, dry eye, eye pain

Postmarketing reports: Acute angle closure glaucoma, increased intraocular pressure

Topiramate:

-Postmarketing reports: Maculopathy

Other

Common (1% to 10%): Fatigue, thirst, procedural pain, chest discomfort, low serum potassium values

Frequency not reported: Pyrexia, ear infection

In 1-year controlled trials of this combination drug, persistent low serum potassium values (less than 3.5 mEq/L at 2 consecutive visits/at the final visit) during the trial occurred in 3.6% and 4.9% of adult patients with phentermine 7.5 mg-topiramate 46 mg and phentermine 15 mg-topiramate 92 mg, respectively; of those reporting persistent low serum potassium, 88% were receiving treatment with a non-potassium sparing diuretic. The incidence of markedly low serum potassium (less than 3 mEq/L and a greater than 0.5 mEq/L reduction from pretreatment) at any time during the trial was 0.2% for phentermine 7.5 mg-topiramate 46 mg and 0.7% for phentermine 15 mg-topiramate 92 mg. Persistent markedly low serum potassium (less than 3 mEq/L and a greater than 0.5 mEq/L reduction from pretreatment at 2 consecutive visits/at the final visit) occurred in 0.2% and 0.1% of patients receiving phentermine 7.5 mg-topiramate 46 mg and phentermine 15 mg-topiramate 92 mg. Low serum potassium levels (less than 3.5 mEq/L) were not observed in a 56-week clinical trial of pediatric patients with obesity.

Psychiatric

Very common (10% or more): Mood/sleep disorders (up to 21%), sleep disorders (up to 11%)

Common (1% to 10%): Insomnia, depression, anxiety, irritability

Frequency not reported: Mood problems

Postmarketing reports: Suicidal ideation, suicidal behavior

Phentermine:

-Postmarketing reports: Euphoria, psychosis, changes in libido

In 1-year controlled trials of this combination drug, 15% and 21% of adult patients reported at least 1 adverse reaction related to mood and sleep disorders with phentermine 7.5 mg-topiramate 46 mg and phentermine 15 mg-topiramate 92 mg, respectively; these events were further categorized into sleep disorders, anxiety, and depression. Reports of sleep disorders were generally characterized as insomnia and occurred in 8.1% and 11% of patients treated with phentermine 7.5 mg-topiramate 46 mg and phentermine 15 mg-topiramate 92 mg, respectively. Reports of anxiety occurred in 4.8% and 7.9% of patients treated with phentermine 7.5 mg-topiramate 46 mg and phentermine 15 mg-topiramate 92 mg, respectively. Reports of depression/mood problems occurred in 3.8% and 7.6% of patients treated with phentermine 7.5 mg-topiramate 46 mg and phentermine 15 mg-topiramate 92 mg, respectively. Mood and sleep disorder adverse reactions occurred in patients with and without history of depression.

In a pediatric clinical trial, more patients treated with this combination drug reported at least 1 adverse reaction related to mood (e.g., depression, anxiety) and sleep disorders (e.g., insomnia) compared to placebo-treated patients.

Renal

Common (1% to 10%): Nephrolithiasis, increased serum creatinine

In 1-year controlled trials of this combination drug, nephrolithiasis was reported in 0.2% and 1.2% of adult patients treated with phentermine 7.5 mg-topiramate 46 mg and phentermine 15 mg-topiramate 92 mg, respectively.

In 1-year controlled trials of this combination drug, serum creatinine increased from baseline, peaking between Week 4 to 8 in adult patients and at Week 16 in pediatric patients; serum creatinine values declined but remained elevated over baseline over 1 year of therapy. The incidence of increases in serum creatinine of at least 0.3 mg/dL at any time during therapy in adult patients was 7.2% for phentermine 7.5 mg-topiramate 46 mg and 8.4% for phentermine 15 mg-topiramate 92 mg; 17% of pediatric patients treated with phentermine 7.5 mg-topiramate 46 mg or phentermine 15 mg-topiramate 92 mg had a serum creatinine at least 0.3 mg/dL at any time post-randomization. Increases in serum creatinine of at least 50% over baseline occurred in 2% and 2.8% of adult patients receiving phentermine 7.5 mg-topiramate 46 mg and phentermine 15 mg-topiramate 92 mg, respectively.

Respiratory

Very common (10% or more): Upper respiratory tract infection (up to 16%), nasopharyngitis (up to 13%)

Common (1% to 10%): Sinusitis, bronchitis, cough, influenza, pharyngolaryngeal pain, nasal congestion, sinus congestion

Frequently asked questions

References

1. Product Information. Qsymia (phentermine-topiramate). Vivus Inc. 2023;SUPPL-23.

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.