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Phentermine / Topiramate Dosage

Medically reviewed by Last updated on Nov 30, 2020.

Applies to the following strengths: 3.75 mg-23 mg; 7.5 mg-46 mg; 11.25 mg-69 mg; 15 mg-92 mg

Usual Adult Dose for Weight Loss

All doses expressed as phentermine/topiramate XR:

Initial dose: 3.75 mg/23 mg orally once a day for 14 days, then 7.5 mg/46 mg orally once a day
-After 12 weeks of dosing at 7.5 mg/46 mg once a day; evaluate weight loss and if weight loss is less than 3% of baseline weight, discontinue therapy or escalate dose:

Dose escalation: 11.25 mg/69 mg orally once a day for 14 days, then 15 mg/92 mg orally once a day
-After 12 weeks of dosing at 15 mg/92 mg once a day; evaluate weight loss and if weight loss is less than 5% of baseline weight, discontinue therapy

Maintenance dose: 7.5 mg/46 mg OR 15 mg/92 mg orally once a day
-Doses of 3.75 mg/23 mg and 11.25 mg/69 mg are for titration purposes only

-Dosing should be in the morning (with or without food) to avoid the possibility of insomnia.
-Doses should be titrated and weight loss evaluated as described above; if percent weight loss is not achieved by stated timeline it is unlikely that patients will achieve and sustain clinically meaningful weight loss and therefore discontinuation is recommended.
-Discontinuation from dose of 15 mg/92 mg once a day should be gradual; decrease to every other day for at least 1 week prior to stopping treatment.

Uses: As an adjunct to a reduced-calorie diet and increased physical activity for chronic weight management in patients:
-With an initial body mass index (BMI) of 30 kg/m2 or greater (obese)
-With an initial BMI of 27 kg/m2 or greater (overweight) in the presence of at least one weight-related comorbidity such as hypertension, type 2 diabetes mellitus, or dyslipidemia.

Renal Dose Adjustments

-Mild renal impairment (CrCl 50 mL/min or more): No adjustment recommended
-Moderate to severe renal impairment (CrCl less than 50 mL/min): Maximum dose: phentermine 7.5 mg/topiramate XR 46 mg orally once a day

Liver Dose Adjustments

-Mild liver impairment (Child-Pugh score 5 to 6): No adjustment recommended
-Moderate liver impairment (Child-Pugh score 7 to 9): Maximum dose: 7.5 mg/topiramate XR 46 mg orally once a day
-Severe liver impairment (Child-Pugh score 10 to 15): Not recommended

Dose Adjustments

Elderly: Dose selection should be cautious

Drug Discontinuation:
-To prevent a possible seizure, discontinue treatment gradually by taking a dose every other day for at least 1 week prior to stopping treatment altogether.


US REMS: The US FDA requires a Risk Evaluation and Mitigation Strategy (REMS) for this drug. It includes a medication guide, elements to assure safe use, and an implementation system. For additional information:

-During or within 14 days following the administration of monoamine oxidase inhibitors
-Known hypersensitivity or idiosyncrasy to the sympathomimetic amines

Safety and efficacy have not been established in patients younger than 18 years.

Consult WARNINGS section for additional precautions.

US Controlled Substance: Schedule IV


Avoid use

Other Comments

Administration advice:
-Take orally in the morning with or without food

Missed dose: If a dose is missed, skip the missed dose and wait until the next morning to take usual dose; do not double dose

-The effect of this drug on cardiovascular morbidity and mortality has not been established.
-The safety and effectiveness of this drug in combination with other weight loss products, including prescription and over-the-counter drugs and herbal preparations, have not been established.
-This drug is only available through certified pharmacies enrolled in the Qsymia certified network; additional information may be obtained via the website

-Obtain a negative pregnancy test before treatment initiation and monthly thereafter in females of reproductive potential.
-Measure blood pressure prior to and during treatment in patients being treated with antihypertensive medications.
-Measure electrolytes including serum bicarbonate prior to and during treatment.
-Monitor patients for the appearance or worsening of metabolic acidosis if they are concomitantly taking a carbonic anhydrase inhibitor and have a predisposing condition for metabolic acidosis.
-Measure blood glucose levels prior to and during treatment in type 2 diabetic patients.
-Monitor for hypokalemia per standard of care.
-Perform appropriate monitoring in situations where immediate termination of this drug is medically required as abrupt withdrawal of topiramate has been associated with seizures in individuals without a history of seizures or epilepsy.
-Monitor for the emergence or worsening of depression, suicidal thoughts or behavior, and/or any unusual changes in mood or behavior.
-Measure serum creatinine levels prior to and during treatment.
-Obtain a blood chemistry profile that includes bicarbonate, creatinine, potassium, and glucose at baseline and periodically during treatment.

Patient Advice:
-Patients should be instructed to read the US FDA-approved patient labeling (Medication Guide).
-Patients should be instructed to follow prescribed diet and exercise plan and maintain adequate hydration.
-Patients should be instructed to report persistently elevated pulse or periods of heart pounding or racing at rest; severe side or back pain and/or blood in their urine; changes in attention, concentration, memory, and/or difficulty finding words; changes in mood or depression, or suicidal ideation; and/or symptoms of severe or persistent eye pain or vision changes.
-Patients should avoid driving or operating hazardous machinery until they gauge how this drug affects their performance.
-Patients should avoid alcohol while on therapy.
-Patients should understand this drug may cause fetal harm; a negative pregnancy test is necessary prior to starting therapy and effective contraception are necessary during therapy.
-Patients should be instructed to monitor for decreased sweating and increased body temperature during physical activity, especially in hot weather.
-Patients with diabetes should be instructed to monitor blood sugars carefully and contact their healthcare provider for changes in glycemic control.
-Patients should be instructed not to abruptly discontinue therapy.

Further information

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