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Drug Interactions With Phentermine and Topiramate

More Detail on Drug Interactions With Phentermine and Topiramate

The following sections explain in detail the potentially negative interactions that can occur when any of the drugs mentioned above are combined with phentermine and topiramate.
 
Alcohol
Combining alcohol and phentermine and topiramate could cause several side effects, including extreme drowsiness and confusion. It is generally advised that people who are taking phentermine and topiramate avoid drinking alcohol.
 
Antacids
Antacids may increase blood levels of phentermine and topiramate, which could increase your risk for side effects. Check with your healthcare provider before taking these medications together.
 
Carbamazepine
Carbamazepine can decrease blood levels of topiramate, one of the active components in the drug, possibly making the medicine less effective. Talk to your healthcare provider about this interaction if you will be taking these medicines together.
 
Carbonic Anhydrase Inhibitors
Combining phentermine and topiramate with medications that are carbonic anhydrase inhibitors can increase your risk of certain side effects, including kidney stones or metabolic acidosis (a condition that occurs when there is too much acid in your body fluids). In general, these medicines should not be taken together.
 
Certain Diuretics
Taking phentermine and topiramate with diuretics ("water pills") that can cause low blood potassium levels (hypokalemia) could increase the risk for hypokalemia. Your healthcare provider may choose to monitor your potassium levels more closely if you take these medicines together. In addition, hydrochlorothiazide (HCTZ) may increase the level of topiramate (one of the active ingredients in the drug) in your blood, possibly increasing your risk of side effects.
 
Diabetes Medicines
Because you may eat less and lose weight while taking phentermine and topiramate, your blood glucose (sugar) levels may decrease. Your healthcare provider may recommend you check your blood glucose levels closely during treatment, and may adjust the dose of your diabetes medications if necessary.  
 
Medications That Cause Drowsiness
Combining phentermine and topiramate with medicines that cause drowsiness could cause several side effects, including extreme drowsiness and confusion. Be extremely careful if you take any medications that cause drowsiness during phentermine and topiramate treatment.
 
Monoamine Oxidase Inhibitors (MAOIs)
Taking phentermine and topiramate with an MAOI can cause life-threatening side effects, such as very high blood pressure. You should not take phentermine and topiramate if you are currently taking an MAOI or have taken an MAOI within the past 14 days.
 
Oral Contraceptives
Most birth control pills contain two types of hormones, an estrogen and a progestin. Phentermine and topiramate may decrease the level of the estrogen portion of birth control pills in your body, and increase the level of progestin in your body. This interaction is not expected to decrease the effectiveness of birth control pills, but may cause irregular bleeding (spotting) between periods. If you have bothersome spotting while taking phentermine and topiramate with a birth control pill, talk to your healthcare provider.  
 
Other Weight Loss Medicines
It is unknown whether phentermine and topiramate is safe when used in combination with other weight loss products, including prescription and over-the-counter weight loss medications. Talk to your healthcare provider before taking other weight loss products while taking phentermine and topiramate.
 
Phenytoin
Phenytoin can decrease blood levels of topiramate, one of the active components of phentermine and topiramate, which could make the medicine less effective. In addition, phentermine and topiramate has the potential to either increase or decrease blood levels of phenytoin. Therefore, your healthcare provider may choose to monitor your phenytoin blood levels if you take these medicines together.
 
Valproate Medicines
Taking phentermine and topiramate with valproic acid can increase your risk for potentially serious side effects, including hyperammonemia (which occurs when you have high levels of ammonia in your blood) and hypothermia. Hyperammonemia and hypothermia can cause serious problems, including brain disease and a coma. Talk to your healthcare provider about this potential interaction before taking these medicines together.
 

More Headlines in Drug Interactions With Phentermine and Topiramate

↶ An Overview of Phentermine and Topiramate Interactions
‣ Final Thoughts
Last reviewed by: Kristi Monson, PharmD
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