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Phentermine and topiramate

Generic Name: phentermine and topiramate (FEN ter meen and toe PIR a mate)
Brand Name: Qsymia

Medically reviewed by on Feb 18, 2019 – Written by Cerner Multum

What is phentermine and topiramate?

Phentermine is an appetite suppressant similar to an amphetamine. Topiramate is a seizure medication, also called an anticonvulsant.

Phentermine and topiramate is a combination medicine used together with diet and exercise to treat obesity. phentermine and topiramate is sometimes used to treat obesity that may be related to diabetes, high cholesterol, or high blood pressure. Phentermine and topiramate will not treat any these underlying conditions. Keep using any other medicines your doctor has prescribed to treat these conditions.

Phentermine and topiramate may also be used for purposes not listed in this medication guide.

Important Information

Do not use if you are pregnant. This medicine may cause birth defects.

You should not use phentermine and topiramate if you have glaucoma or overactive thyroid.

Do not use phentermine and topiramate if you have used an MAO inhibitor in the past 14 days. A dangerous drug interaction could occur. MAO inhibitors include isocarboxazid, linezolid, methylene blue injection, phenelzine, rasagiline, selegiline, tranylcypromine, and others.

Before taking this medicine

Do not use phentermine and topiramate if you have used an MAO inhibitor in the past 14 days. A dangerous drug interaction could occur. MAO inhibitors include isocarboxazid, linezolid, methylene blue injection, phenelzine, rasagiline, selegiline, tranylcypromine, and others.

You should not use phentermine and topiramate if you are allergic to phentermine or topiramate, or if you have:

  • glaucoma;

  • overactive thyroid; or

  • if you are pregnant or may become pregnant.

To make sure this medicine is safe for you, tell your doctor if you have:

Do not use if you are pregnant, and use effective birth control to prevent pregnancy while taking phentermine and topiramate. This medicine can harm an unborn baby or cause birth defects. Weight loss during pregnancy also can harm an unborn baby, even if you are overweight. You may need to have a negative pregnancy test before starting this treatment.

Phentermine and topiramate can cause irregular vaginal bleeding while you are taking birth control pills. This should not make the pills less effective in preventing pregnancy.

It is not known whether phentermine and topiramate passes into breast milk or if it could harm a nursing baby. You should not breast-feed while using this medicine.

Phentermine and topiramate is not approved for use by anyone younger than 18 years old.

How should I take phentermine and topiramate?

Follow all directions on your prescription label. Your doctor may occasionally change your dose to make sure you get the best results. Do not use this medicine in larger or smaller amounts or for longer than recommended.

Phentermine may be habit-forming. Never share this medicine with another person, especially someone with a history of drug abuse or addiction. Keep the medication in a place where others cannot get to it. Selling or giving away this medicine is against the law.

You may take this medicine with or without food.

Do not crush, chew, break, or open an extended-release capsule. Swallow it whole.

Drink plenty of water each day to prevent dehydration or kidney stones while you are taking phentermine and topiramate. You can easily become dehydrated while taking this medicine, which can lead to severely low blood pressure or a serious electrolyte imbalance.

You should lose at least 3% of your starting weight during the first 12 weeks of taking this medicine and eating a low calorie diet. Tell your doctor if you do not lose at least 3% of your starting weight after taking this medicine for 12 weeks.

Talk with your doctor if you feel very hungry and think the medicine is not working properly. Taking more medicine will not make it more effective and can cause serious, life-threatening side effects.

You should not stop using phentermine and topiramate suddenly or you could have a seizure (convulsions). Follow your doctor's instructions about tapering your dose.

Store at room temperature away from moisture and heat. Keep track of the amount of medicine used from each new bottle. Phentermine is a drug of abuse and you should be aware if anyone is using your medicine improperly or without a prescription.

What happens if I miss a dose?

Take the missed dose as soon as you remember. Skip the missed dose if it is almost time for your next scheduled dose. Do not take extra medicine to make up the missed dose.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222. An overdose of phentermine and topiramate can be fatal.

Overdose symptoms may include confusion, hallucinations, panic, tremors, nausea, vomiting, diarrhea, stomach cramps, irregular heartbeat, rapid breathing, seizure (convulsions), and restless feeling followed by severe tiredness.

What should I avoid while taking phentermine and topiramate?

Ketogenic or "ketosis" diets that are high in fat and low in carbohydrates can increase the risk of kidney stones. Avoid the use of such diets while you are taking phentermine and topiramate.

This medicine may cause blurred vision and may impair your thinking or reactions. Be careful if you drive or do anything that requires you to be alert and able to see clearly.

Drinking alcohol with this medicine can cause side effects.

Do not take any other weight-loss products without your doctor's advice.

Phentermine and topiramate side effects

Get emergency medical help if you have signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat.

Report any new or worsening symptoms to your doctor, such as: mood or behavior changes, anxiety, panic attacks, trouble sleeping, or if you feel impulsive, irritable, agitated, hostile, aggressive, restless, hyperactive (mentally or physically), more depressed, or have thoughts about suicide or hurting yourself.

Call your doctor at once if you have:

  • pounding heartbeats or fluttering in your chest (even if you are resting);

  • sudden vision problems, sometimes with eye pain or redness;

  • trouble concentrating, problems with speech or memory;

  • a seizure (convulsions);

  • feeling very thirsty or hot, decreased sweating, hot and dry skin;

  • low blood sugar--headache, hunger, weakness, sweating, irritability, dizziness, or feeling jittery;

  • signs of metabolic acidosis--confusion, vomiting, lack of energy, irregular heartbeats; or

  • signs of a kidney stone--pain in your side or lower back, blood in your urine, painful or difficult urination.

Common side effects may include:

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Phentermine and topiramate dosing information

Usual Adult Dose for Weight Loss:

All doses expressed as phentermine/topiramate:

Initial dose: 3.75 mg/23 mg orally once a day for 14 days, then 7.5 mg/46 mg orally once a day
-Evaluate weight loss after 12 weeks at 7.5 mg/46 mg; 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
-Evaluate weight loss after 12 weeks at 15 mg/92 mg; if weight loss is less than 5% of baseline weight, discontinue therapy.

Maintance dose: 7.5 mg/46 mg OR 15 mg/92 mg orally once a day

-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.

What other drugs will affect phentermine and topiramate?

Taking phentermine and topiramate with other drugs that make you sleepy can worsen this effect. Ask your doctor before taking phentermine and topiramate with a sleeping pill, narcotic pain medicine, muscle relaxer, or medicine for anxiety, depression, or seizures.

Tell your doctor about all your current medicines and any you start or stop using, especially:

This list is not complete. Other drugs may interact with phentermine and topiramate, including prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible interactions are listed in this medication guide.

Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use this medication only for the indication prescribed.

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