What Is Phentermine/Topiramate XR? Uses, Dosage, and What You Need to Know in 2026

Phentermine/topiramate extended-release — sold under the brand name Qsymia — is an FDA-approved prescription medication for chronic weight management. It's a once-daily oral capsule that combines two active ingredients to reduce appetite and support long-term weight loss. Here's everything you need to know about what it is, who it's for, and how it's used.

What Is Phentermine/Topiramate XR?

Phentermine/topiramate XR is a combination medication that pairs two drugs with different mechanisms of action to produce greater weight loss than either drug achieves alone:

Phentermine is a sympathomimetic amine that acts as an appetite suppressant. It stimulates the release of norepinephrine in the hypothalamus, the brain's appetite control center, reducing hunger signals.

Topiramate is an anticonvulsant that enhances feelings of fullness and reduces food cravings, though its exact weight loss mechanism isn't fully understood.

The phentermine is formulated as immediate-release; the topiramate is extended-release (XR), which means it's slowly released over several hours. This combination produces sustained appetite suppression throughout the day with a single morning dose.

What Is It Approved to Treat?

Phentermine/topiramate XR is FDA-approved for chronic weight management as an adjunct to a reduced-calorie diet and increased physical activity in:

Adults with a BMI ≥30 (classified as obese)

Adults with a BMI ≥27 plus at least one weight-related comorbidity (hypertension, type 2 diabetes, or dyslipidemia)

Pediatric patients ages 12 and older with obesity (BMI ≥95th percentile for age and sex) — approved in 2022

Qsymia was first approved in July 2012 for adults, making it one of the first modern long-term obesity medications. The generic became available in May 2025.

What Are the Dosage Strengths?

Phentermine/topiramate XR comes in four extended-release capsule strengths:

3.75 mg/23 mg — starter dose (first 14 days)

7.5 mg/46 mg — recommended maintenance dose

11.25 mg/69 mg — titration dose (14 days before escalating to maximum)

15 mg/92 mg — maximum dose

How Is It Taken?

One capsule taken orally once daily in the morning, with or without food. It's important to take it in the morning — the phentermine component can cause insomnia if taken later in the day. Do not crush, chew, or break the capsule (it's extended-release).

The standard titration schedule:

Start with 3.75/23 mg once daily for 14 days

Increase to 7.5/46 mg once daily (the target maintenance dose for most patients)

At 12 weeks, if less than 3% weight loss (adults) or BMI reduction (pediatrics), titrate to 11.25/69 mg for 14 days, then to 15/92 mg

At 12 weeks on maximum dose, if less than 5% weight loss, discontinue gradually

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How Effective Is It?

Phentermine/topiramate XR is one of the most effective oral weight loss medications currently available. In a one-year clinical trial (EQUIP), 70% of adults taking the maximum dose achieved at least 5% body weight loss, and nearly half achieved 10% or more. Average weight loss was approximately 17 pounds more than placebo. For adolescents, BMI reductions of 4.8–7.1% were observed in 56-week trials versus a 3.3% BMI increase in placebo.

Who Should NOT Take Phentermine/Topiramate XR?

Phentermine/topiramate XR is contraindicated in:

Pregnant patients (serious birth defect risk)

Patients with glaucoma

Patients with hyperthyroidism

Patients taking MAOIs or who have taken them within the past 14 days

Patients with hypersensitivity to phentermine, topiramate, or sympathomimetic amines

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The REMS Program: Why You Can Only Get It at Certain Pharmacies

Because topiramate can cause serious birth defects, the FDA requires a Risk Evaluation and Mitigation Strategy (REMS) for phentermine/topiramate XR. This means it can only be dispensed at certified pharmacies — not every pharmacy can fill this prescription. For patients who can become pregnant, monthly pregnancy testing is required during treatment.

For help locating a certified pharmacy near you, see our pharmacy search guide. For a complete overview of what to watch out for on this medication, read our side effects guide.