Phentermine and topiramate (Oral)
Medically reviewed by Drugs.com. Last updated on Mar 2, 2022.
Commonly used brand name(s)
In the U.S.
Available Dosage Forms:
- Capsule, Extended Release
Therapeutic Class: Appetite Suppressant, Centrally Acting
Chemical Class: Phentermine
Uses for phentermine and topiramate
Phentermine and topiramate combination is used together with a reduced-calorie diet and proper exercise to help you lose weight. It is also used in overweight people who may also have diabetes, high blood pressure, high cholesterol, or heart disease.
Phentermine and topiramate is available only under a special restricted distribution program called Qsymia™ REMS program.
Before using phentermine and topiramate
In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For phentermine and topiramate, the following should be considered:
Tell your doctor if you have ever had any unusual or allergic reaction to phentermine and topiramate or any other medicines. Also tell your health care professional if you have any other types of allergies, such as to foods, dyes, preservatives, or animals. For non-prescription products, read the label or package ingredients carefully.
Appropriate studies have not been performed on the relationship of age to the effects of phentermine and topiramate combination in the pediatric population. Safety and efficacy have not been established.
Appropriate studies performed to date have not demonstrated geriatric-specific problems that would limit the usefulness of phentermine and topiramate combination in the elderly. However, elderly patients are more likely to have kidney, liver, or heart problems, which may require caution and an adjustment in the dose for patients receiving phentermine and topiramate combination.
There are no adequate studies in women for determining infant risk when using this medication during breastfeeding. Weigh the potential benefits against the potential risks before taking this medication while breastfeeding.
Interactions with medicines
Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. When you are taking phentermine and topiramate, it is especially important that your healthcare professional know if you are taking any of the medicines listed below. The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive.
Using phentermine and topiramate with any of the following medicines is not recommended. Your doctor may decide not to treat you with this medication or change some of the other medicines you take.
- Methylene Blue
Using phentermine and topiramate with any of the following medicines is usually not recommended, but may be required in some cases. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.
- Calcium Oxybate
- Ethinyl Estradiol
- Gabapentin Enacarbil
- Iobenguane I 131
- Magnesium Oxybate
- Morphine Sulfate Liposome
- Potassium Oxybate
- Ropeginterferon Alfa-2b-njft
- Sodium Oxybate
Using phentermine and topiramate with any of the following medicines may cause an increased risk of certain side effects, but using both drugs may be the best treatment for you. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.
- Valproic Acid
Interactions with food/tobacco/alcohol
Certain medicines should not be used at or around the time of eating food or eating certain types of food since interactions may occur. Using alcohol or tobacco with certain medicines may also cause interactions to occur. The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive.
Using phentermine and topiramate with any of the following is not recommended. Your doctor may decide not to treat you with this medication, change some of the other medicines you take, or give you special instructions about the use of food, alcohol, or tobacco.
Other medical problems
The presence of other medical problems may affect the use of phentermine and topiramate. Make sure you tell your doctor if you have any other medical problems, especially:
- Allergy to similar medicines (e.g., adrenaline, amphetamine, dopamine, dobutamine, ephedrine, or lisdexamfetamine) or
- Glaucoma or
- Hyperthyroidism (overactive thyroid)—Should not be used in patients with these conditions.
- Bone problems (e.g., osteoporosis) or
- Depression, history of or
- Drug abuse or dependence, history of or
- Eye or vision problems or
- Hypokalemia (low potassium in the blood) or
- Kidney stones, history of or
- Mental illness, history of or
- Metabolic acidosis (too much acid in the blood), history of or
- Seizures or epilepsy, history of—Use with caution. May make these conditions worse.
- Diarrhea or
- Ketogenic diet (high-fat, low-protein, low-carbohydrate diet) or
- Kidney problems or
- Lung disease or other breathing problems or
- Status epilepticus (e.g., a state of epilepsy where you have many seizures in a row and do not gain consciousness) or
- Surgery—These problems may make a condition called metabolic acidosis occur or make it worse.
- Heart or blood vessel disease, unstable—Use is not recommended in patients with these conditions.
- Kidney disease, moderate or severe or
- Liver disease, moderate—Use with caution. The effects may be increased because of slower removal of the medicine from the body.
Proper use of phentermine and topiramate
Take phentermine and topiramate only as directed by your doctor. Do not take more of it, do not take it more often, and do not take it for a longer time than your doctor ordered. If too much is taken, it may become habit-forming (causing mental or physical dependence).
Phentermine and topiramate comes with a Medication Guide. Read and follow the instructions carefully. Ask your doctor if you have any questions.
Take phentermine and topiramate once a day in the morning, with or without food. Avoid taking phentermine and topiramate in the evening to prevent trouble sleeping.
Swallow the extended-release capsule whole. Do not crush, break, or chew it.
Carefully follow your doctor's instructions for a reduced-calorie diet plan and regular exercise. Talk with your doctor before starting any exercise program.
Your doctor should tell you to stop taking phentermine and topiramate if you do not lose a certain amount of weight within the first 12 weeks of treatment.
It is important that you drink extra water every day while you take phentermine and topiramate to help prevent kidney stones.
The dose of phentermine and topiramate will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of phentermine and topiramate. If your dose is different, do not change it unless your doctor tells you to do so.
The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.
- For oral dosage form (extended-release capsules):
- For weight loss:
- Adults—At first, one tablet of 3.75 milligrams (mg) of phentermine and 23 mg of topiramate once a day for 14 days. After 14 days, your doctor may increase your dose to 7.5 mg of phentermine and 46 mg of topiramate once a day. Then, your doctor may increase your dose as needed up to 15 mg of phentermine and 92 mg of topiramate.
- Children—Use is not recommended.
- For weight loss:
If you miss a dose of phentermine and topiramate, take it as soon as possible. However, if it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule. Do not double doses.
Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light. Keep from freezing.
Keep out of the reach of children.
Do not keep outdated medicine or medicine no longer needed.
Ask your healthcare professional how you should dispose of any medicine you do not use.
Precautions while using phentermine and topiramate
It is very important that your doctor check your progress at regular visits, to make sure that phentermine and topiramate is working properly. Blood and urine tests may be needed to check for unwanted effects.
Using phentermine and topiramate while you are pregnant can harm your unborn baby. Use an effective form of birth control to keep from getting pregnant. If you think you have become pregnant while using phentermine and topiramate, tell your doctor right away.
You must have a negative pregnancy test before you will be allowed to take phentermine and topiramate. You will also be required to have a pregnancy test every month during your treatment. If you miss a period while you are using phentermine and topiramate, tell your doctor right away.
Do not use phentermine and topiramate if you have used an MAO inhibitor (MAOI) such as Eldepryl®, Marplan®, Nardil®, or Parnate® within the past 14 days. Using these medicines together may cause serious unwanted effects.
Phentermine and topiramate may be habit-forming. If you think phentermine and topiramate is not working properly after you have taken it for a few weeks, do not increase the dose. Instead, check with your doctor.
Phentermine and topiramate may increase your heart rate. Check with your doctor right away if you have a racing heartbeat while at rest after taking phentermine and topiramate.
Phentermine and topiramate may cause some people to be agitated, irritable, or display other abnormal behaviors. It may also cause some people to have suicidal thoughts and tendencies or to become more depressed. If you or your caregiver notice any of these side effects, tell your doctor right away.
Check with your doctor immediately if you have a decrease in vision, blurred vision, or pain around the eyes during and after treatment with phentermine and topiramate. Your doctor may want you to have your eyes checked by an eye doctor.
Phentermine and topiramate may cause some people to become dizzy, drowsy, or have trouble in thinking or speaking. Make sure you know how you react to phentermine and topiramate before you drive, use machines, or do anything else that could be dangerous if you are not alert, well-coordinated, or able to think or see well.
Phentermine and topiramate may cause nausea, muscle tremors, fast breathing, problems eating, fast heartbeat, restlessness, and abdominal or stomach pain. Tell your doctor right away if you have any of these symptoms. This may be a sign that you may be having a metabolic acidosis (too much acid in the blood).
For diabetic patients: Phentermine and topiramate may affect blood sugar levels. If you notice a change in the results of your blood or urine sugar tests or if you have any questions, check with your doctor.
For patients with high blood pressure: Phentermine and topiramate may increase risk of lowering your blood pressure. If you feel dizzy, faint, or lightheaded after taking phentermine and topiramate, check with your doctor.
Phentermine and topiramate will add to the effects of alcohol and other CNS depressants (medicines that make you drowsy or less alert). Some examples of CNS depressants are antihistamines or medicine for hay fever, other allergies, or colds, prescription pain medicines, or sleep medicines. Check with your doctor before taking any of the above while you are using phentermine and topiramate.
Do not suddenly stop taking phentermine and topiramate without first checking with your doctor. Stopping the medicine suddenly may cause your seizures to return or to occur more often. Your doctor may want you to gradually reduce the amount you are using before stopping completely.
Check with your doctor right away if you have sudden back pain, abdominal or stomach pain, pain while urinating, or bloody or dark urine. These may be symptoms of kidney stones.
Phentermine and topiramate may make you sweat less, causing your body temperature to increase. Use extra care not to become overheated during exercise or hot weather while you are taking phentermine and topiramate. Overheating may result in heat stroke. Also, hot baths or saunas may make you dizzy or faint while you are taking phentermine and topiramate.
Phentermine and topiramate may cause your body temperature to go down especially when taking valproic acid, which is a medicine to control seizures. You may have tiredness, weakness, confusion, and abnormal heartbeat and breathing. Tell your doctor right away if you feel any of these side effects.
Birth control pills (containing estrogen) may not work properly if you take them while you are taking phentermine and topiramate. Unplanned pregnancies may occur. You should use a different or additional means of birth control while you are using phentermine and topiramate. If you have any questions about this, check with your doctor or pharmacist.
Check with your doctor right away if you are having unusual drowsiness, dullness, tiredness, weakness, or feelings of sluggishness, mental depression or anxiety, nightmares or unusually vivid dreams, or vomiting. These may be symptoms of a serious condition called hyperammonemic encephalopathy.
Do not take other medicines unless they have been discussed with your doctor. This includes prescription or nonprescription (over-the-counter [OTC]) medicines and herbal or vitamin supplements (including any weight loss products).
Phentermine and topiramate side effects
Along with its needed effects, a medicine 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:
- Chest discomfort
- decreased urine
- fast, irregular, pounding, or racing heartbeat or pulse
- loss of appetite
- mood changes
- muscle pain or cramps
- nausea or vomiting
- numbness or tingling in the hands, feet, or lips
- shortness of breath
- unusual tiredness or weakness
- Blood in the urine
- pain in the groin or genitals
- sharp back pain just below the ribs
Incidence not known
- Blistering, peeling, or loosening of the skin
- blisters on the mouth, trunk, scalp, or other areas
- blurred or decreased vision
- chest pain
- chills or shivering
- continuing nausea or vomiting
- cough or sore throat
- dark urine
- diarrhea or light-colored stools
- increase in the frequency of seizures
- irregular heartbeat
- joint or muscle pain
- loss of appetite
- low body temperature
- muscle aches or weakness
- pain in the shoulders, arms, jaw, or neck
- red skin lesions, often with a purple center
- red, irritated eyes
- shakiness in the legs, arms, hands, or feet
- sores, ulcers, or white spots in the mouth or on the lips
- swelling of the face
- tiredness and weakness
- trouble thinking, speaking, or walking
- upper right abdominal or stomach pain
- weak or feeble pulse
- weight gain
- yellow eyes or skin
Some side effects 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:
- Back pain
- change in taste
- difficulty having a bowel movement (stool)
- ear congestion
- fear or nervousness
- loss of taste
- loss of voice
- memory problems
- pain or tenderness around the eyes and cheekbones
- stuffy or runny nose
- trouble sleeping
- decreased appetite
- dry eyes
- eye pain
- hair loss
- heartburn or indigestion
- heavy bleeding
- stomach discomfort, upset, or pain
Incidence not known
- false or unusual sense of well-being
- feeling that others are watching you or controlling your behavior
- feeling that others can hear your thoughts
- feeling, seeing, or hearing things that are not there
- hives or welts
- change in sexual ability, desire, drive, or performance
- severe mood or mental changes
- unusual behavior
Other side effects not listed may also occur in some patients. If you notice any other effects, check with your healthcare professional.
Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.
More about phentermine / topiramate
- Side effects
- Drug interactions
- Dosage information
- During pregnancy
- Reviews (676)
- En español
- Drug class: anorexiants
- Other brands
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