Qsymia dosage, forms, and strengths

Qsymia (phentermine/topiramate) is a brand-name weight loss medication that combines phentermine with the anticonvulsant topiramate. Both of these medications suppress appetite to reduce food intake. Qsymia tablets are taken once per day in the morning. Phentermine is a controlled substance and potentially hazardous, so healthcare providers are careful when prescribing Qsymia. 

Qsymia forms and strengths

• Extended-release capsules: 3.75 mg phentermine/23 mg topiramate, 7.5 mg/46 mg, 11.25 mg/69 mg, 15 mg/92 mg

Qsymia dosage for adults

Qsymia is an appetite suppressant prescribed to adults and children 12 years and older who are diagnosed as obese. The FDA has also approved its use to treat excess weight in adults who have weight-related comorbidities, such as high blood pressure (hypertension), high cholesterol, or Type 2 diabetes. 

Qsymia is not right for everyone. People who are pregnant or have hyperthyroidism, glaucoma, or allergies to phentermine or topiramate cannot safely take Qsymia. Phentermine can cause birth defects, so a negative pregnancy test is necessary before the drug can be started.

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Qsymia dosage for weight management

Qsymia is an appetite suppressant that reduces hunger, speeds up the feeling of fullness, and reduces the amount of food people eat. The drug contains two active ingredients: phentermine and topiramate. Both work by affecting the brain. 

Phentermine is a stimulant that works much like an amphetamine, one of the first types of drugs used to reduce appetite. As a stimulant, it makes the brain more active. Like amphetamines, it’s a controlled substance that can lead to abuse and dependency. When phentermine is used as a standalone therapy for weight management, doctors only prescribe it as a short-term treatment. However, the amount of phentermine in the recommended dose of Qsymia is only 1/5 of the recommended dose of standalone phentermine therapy.

Topiramate is an anticonvulsant primarily used to treat seizures and migraines. Unlike phentermine, topiramate slows down the brain. It can also suppress appetite, though healthcare professionals are unsure how it works. It may also lead to early satiety, making people feel full with smaller meal portions.

Starting doses are small, but after 14 days, the dose will increase to the recommended Qsymia dose of 7.5 mg/46 mg once-daily capsules. The prescriber will meet with the patient after 12 weeks of treatment. If not enough body weight has been shed, the doctor may prescribe a higher dose for 14 days and then prescribe the maximum dose for another three months. If minimal weight loss goals have not been met at the end of that period, the doctor will discontinue Qsymia. 

Qsymia doses are taken once daily in the morning. They can be taken with or without food. Taking Qsymia capsules late in the day is not a good idea because the phentermine might keep you up all night.

• Standard Qsymia dosage for weight management: 7.5 mg/46 mg–15 mg/92 mg capsule taken once daily in the morning

• Maximum Qsymia dosage for weight management: 15 mg/92 mg capsule taken once daily in the morning

Qsymia dosage for children

Qsymia is FDA-approved to treat pediatric patients diagnosed with obesity who are 12 years of age or older. The doses are the same as for adults.

Again, doses will start small for 14 days and increase to the recommended dose of 7.5 mg/46 mg. After three months, the doctor will meet with the teen and assess weight loss goals. If the child has not dropped 3% of their initial BMI, the doctor will increase the dose for 14 days and then prescribe the maximum dose for another three months. At that time, if the child has not lost at least 5% of their initial BMI, the prescriber will stop Qsymia treatment.

• Standard Qsymia dosage for children ages 12 and older: 7.5 mg/46 mg–15 mg/92 mg capsule taken once daily in the morning

• Maximum Qsymia dosage for children ages 12 and older: 15 mg/92 mg capsule taken once daily in the morning

Qsymia dosage restrictions

Healthcare professionals may limit the dose or avoid Qsymia altogether in people with kidney problems or liver problems:

• Patients with renal impairment (kidney disease): 

  • Mild kidney impairment (creatinine clearance between 50 mL/min and 80 mL/min): No adjustment

  • Moderate to severe kidney impairment (creatinine clearance <50 mL/min): Maximum dosage is 7.5 mg/46 mg once daily

  • End-stage kidney disease or dialysis: Avoid use

• Patients with hepatic impairment (liver problems): 

  • Mild liver disease (Child-Pugh Class A): No dose adjustment

  • Moderate liver disease (Child-Pugh Class B): Maximum dosage is 7.5 mg/46 mg once daily

  • Severe liver disease (Child-Pugh Class C): Avoid use

How to take Qsymia

There’s nothing particularly special about taking Qsymia other than making sure the dose is taken early in the morning:

• Take Qsymia as directed. Do not take it more than prescribed or take doses more often than prescribed. 

• The dose will change during treatment, but the prescription will reflect any dose change.

• Qsymia works best when used with a reduced-calorie diet and regular exercise.

• Please read the medication guide before taking Qsymia. It contains valuable information and medical advice.

• Qsymia can be taken with or without food.

• Take each dose in the morning. Taking it later in the day may cause sleep problems.

• Swallow the extended-release capsule whole. Do not crush, break, or chew them.

• Drink extra fluids to avoid possible kidney problems.

• Store Qsymia capsules in a tightly closed container in a dry place at room temperature. Keep the drug away from moisture.

Qsymia dosage FAQs

How long does it take Qsymia to work?

Weight loss is a slow process, and Qsymia is a long-term treatment. In clinical trials, participants lost an average of 15 to 19 pounds in three months and 22 to 29 pounds in a year. The success of therapy should be evident after 14 weeks. By that time, adults should have lost at least 3% of their body weight, and adolescents should have dropped 3% of their body mass index (BMI). 

How long does Qsymia stay in your system?

Both phentermine and topiramate are long-lasting drugs. With a half-life of 20 hours, it takes the body almost three days to completely clear the phentermine in a Qsymia dose. Topiramate lasts much longer. With a half-life of 65 hours, the topiramate in a dose of Qsymia can stay in the system for over a week.

What happens if I miss a dose of Qsymia?

Skip any missed dose. Take the next day’s dose as scheduled in the morning. Never take an extra capsule to make up for a missed dose. 

How long can you take Qsymia?

Qsymia is intended for long-term use, which can last several months to over a year. 

How do I stop taking Qsymia?

The prescriber will need to gradually reduce the dose when it’s time to stop therapy, so don’t quit taking Qsymia until talking to the doctor. When suddenly discontinued, both phentermine and topiramate can cause withdrawal symptoms, including seizures, fatigue, and depression.

The doctor will likely stop the prescription if it causes significant adverse effects or weight loss goals are not met. If drug therapy is still warranted, ask the prescriber about other medical treatments, including:

• GLP-1 receptor agonists such as Ozempic

• Contrave (bupropion-naltrexone)

• Other stimulants

• Orlistat

Non-medication alternatives include Plenity, a gel capsule that expands in the stomach, and alternative therapies.

What is the maximum dosage for Qsymia?

The maximum dosage for Qsymia is 15 mg/92 mg once daily. 

Can you overdose on Qsymia?

Both topiramate and phentermine can cause serious problems when too much is taken. People who take bigger doses than prescribed may feel restless, confused, or violent. They may have hallucinations, tremors, nausea, abdominal cramps, diarrhea, or overactive reflexes. A large overdose can speed up the heart rate, disrupt heartbeat rhythms, raise or lower blood pressure, and bring on convulsions. Both phentermine and topiramate have caused fatalities with large enough doses.

People can also overdose on Qsymia by taking it more often than prescribed. Over time, chronic use or misuse of Qsymia can cause sleeplessness, mood changes, irritability, and personality changes. At worst, chronic misuse of Qsymia can bring on psychosis. 

What interacts with Qsymia?

Qsymia has some significant drug interactions, so make sure to tell the prescribing healthcare provider about all prescription drugs, over-the-counter medications, and supplements being used, particularly:

• Monoamine oxidase inhibitors (MAOIs)—contraindicated with Qsymia

• Other stimulants

• Other weight loss medications, including over-the-counter formulations

• Other epilepsy drugs, such as valproic acid

• Birth control pills

• Drugs (CNS depressants) that make you sleepy, such as narcotic pain relievers, sleeping pills, benzodiazepines, barbiturates, antihistamines, or alcohol 

• Drugs that make you pee (diuretics)

• Drugs that treat Type 2 diabetes

• Glaucoma drugs called carbonic anhydrase inhibitors, such as acetazolamide, zonisamide, or methazolamide

What happens when you mix Qsymia and alcohol?

Avoid alcohol when taking Qsymia. The combination can worsen Qsymia side effects, such as sleepiness and dizziness. 

Is it safe to take Qsymia during pregnancy?

Do not get pregnant when taking Qsymia. The drug can harm an unborn fetus, so it’s only available through a special program at certain pharmacies. Healthcare professionals will perform a pregnancy test before prescribing Qsymia. Women should use effective contraception when on this medicine.

Is it safe to take Qsymia while breastfeeding?

Breastfeeding is not recommended in women taking Qsymia. Both phentermine and topiramate will be present in human breast milk if taken. Topiramate can cause sleepiness and diarrhea in a nursing infant. Healthcare professionals are uncertain if phentermine can also cause problems in the baby.

What are the side effects of Qsymia?

The most common side effects of Qsymia in adults are numbness, tingling, dizziness, taste changes, trouble sleeping, constipation, and dry mouth. The most common side effects in children are depression, dizziness, joint pain, fever, and flu.

What are the serious side effects of Qsymia?

The most serious adverse effects of Qsymia are kidney problems, kidney stones, high acid in the blood (metabolic acidosis), high ammonia in the blood, depression, suicidal thoughts or actions, mood disorders, eye problems, vision loss, body temperature dysregulation, low potassium (hypokalemia), low glucose levels in people with Type 2 diabetes, and severe skin reactions.

Sources

• Phentermine hydrochloride tablet, phentermine hydrochloride capsule, DailyMed (2024)

• Qsymia, Vivus LLC (2024)

• Qsymia, Vivus LLC (2024)

• Qsymia- phentermine and topiramate capsule, extended release, DailyMed (2024)