8 Qsymia Interactions to Consider
Key takeaways:
Qsymia (phentermine / topiramate) is an FDA-approved weight loss medication. It can interact with amitriptyline, diuretics, and some anti-seizure medications.
You shouldn’t take Qsymia with monoamine oxidase inhibitors (MAOIs) or other medications that contain phentermine or topiramate. It’s also best to limit alcohol and avoid taking other sedating medications with Qsymia.
Qsymia can raise the risk of breakthrough bleeding if you take it with birth control pills. If you’re taking birth control pills with Qsymia, you’ll need to add a second form of birth control. This is because Qsymia has a high risk of birth defects if you become pregnant while taking it.
Table of contents
Qsymia (phentermine / topiramate) is a combination medication that’s FDA-approved for weight loss. It contains two active ingredients: phentermine and topiramate. Qsymia works by reducing your appetite and making you feel full faster. It should be combined with regular exercise and a balanced diet.
Like other medications, Qsymia also has interactions to be aware of when you’re taking it. Here, we'll focus on eight Qsymia interactions you should know about. Keep in mind that this isn’t a complete list — your healthcare provider or pharmacist can let you know about any other interactions that may apply to you.
1. Oral contraceptive pills
Oral contraceptive pills (birth control pills) can interact with Qsymia. Qsymia may change the levels of oral contraceptive hormones in the body. This shouldn't change their effectiveness, but it can cause breakthrough bleeding or spotting for some people. So it may help to carry extra protection with you in case spotting happens when you’re not expecting it. And you should let your healthcare provider know if it’s happening often. They may recommend a different form of birth control for you.
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Keep in mind: If you’re taking birth control pills to prevent pregnancy, an additional birth control method is necessary while you’re taking Qsymia. This is because Qsymia can cause serious fetal harm if you become pregnant while taking it, and birth control pills can be unreliable on their own, especially if you forget to take one. The FDA’s Qsymia Risk Evaluation and Mitigation Strategy (REMS) program requires a negative pregnancy test before starting Qsymia and monthly negative tests during treatment.
2. Alcohol
Alcohol can also interact with Qsymia. Combining Qsymia with alcohol can increase your risk of side effects, such as dizziness, drowsiness, and trouble concentrating. This is because alcohol and Qsymia affect your brain in similar ways.
It’s best to limit or avoid alcohol consumption while on Qsymia. If you're a regular drinker, let your healthcare provider know before starting Qsymia. They can help you safely reduce your alcohol intake. Or they may recommend a different weight loss medication that’s safe for you.
If you or someone you know struggles with substance use, help is available. Call SAMHSA’s National Helpline at 1-800-662-4357 to learn about resources in your area.
3. CNS depressants
Central Nervous System (CNS) depressants, or sedatives, are medications that slow down brain activity. They include benzodiazepines, barbiturates, and opioids. Some sleep medications and antihistamines are sedatives, too. These medications can cause drowsiness and dizziness. Taking them with Qsymia can worsen these side effects. The combination can also increase the chance of confusion and trouble speaking or thinking.
Be sure your healthcare provider knows if you’re taking any CNS depressants before starting Qsymia. They may want to make changes to your dose or your medications due to this interaction. Even if your provider OKs combining Qsymia with one of these medications, avoid driving or doing other tasks that require your full attention until you know how the combination affects you.
4. Other weight loss medications
As mentioned, Qsymia is a combination medication that contains phentermine and topiramate. Phentermine (Adipex-P) is also available on its own for weight loss. Topiramate (Topamax) is also available on its own, although taking it for weight loss is an off-label usage.
Taking more than one medication with the same ingredient isn’t recommended, as it can increase side effects and may be harmful to your health.
Can I take more than one weight loss medication at a time?
The effect of taking more than one weight loss medication at a time hasn’t been studied. So we don’t know much about the possible risks and benefits of combining different types of weight loss medications.
In most cases, if one weight loss medication isn’t effective for you, you’ll stop taking it before trying a new one. You should only combine more than one medication if your provider tells you to. They’ll be able to make sure the combination is safe based on your medical history.
Keep in mind: This also applies to over-the-counter (OTC) herbs and supplements that claim to help with weight loss. You shouldn’t take them with Qsymia unless your provider OKs it.
5. Amitriptyline
Amitriptyline is an antidepressant that’s also used off-label for insomnia and nerve pain. Qsymia can increase levels of amitriptyline in your body. That can raise the risk of amitriptyline side effects, such as dry mouth and constipation.
Your healthcare provider may keep a close eye on your symptoms if you’re taking Qsymia and amitriptyline together. They may need to lower your amitriptyline dosage if side effects become bothersome.
6. Monoamine oxidase inhibitors (MAOIs)
Monoamine oxidase inhibitors (MAOIs) are another class of medications that can interact with Qsymia. MAOIs are used to treat depression and Parkinson’s disease. Examples include rasagiline (Azilect) and selegiline.
Taking Qsymia with MAOIs can increase the risk for dangerously high blood pressure (hypertensive crisis). This can be dangerous if it’s not treated right away. Because of this risk, it’s not recommended to take Qsymia and MAOIs together. And you shouldn’t start Qsymia until at least 14 days after you stop taking an MAOI. But don’t stop taking an MAOI on your own. Your provider can prescribe a safer weight loss medication for you if you’re taking an MAOI.
7. Certain anti-seizure medications
Qsymia can also interact with certain anti-seizure medications.
Carbamazepine (Tegretol) and phenytoin (Dilantin) can lower Qsymia levels in the body, which can make it less effective.
Valproic acid (Depakote) may raise blood ammonia levels and/or cause a dangerous drop in body temperature if combined with Qsymia. Certain people may be more at risk for this side effect.
You may need a different weight loss option if you’re taking anti-seizure medication. Your provider will help decide what’s best for your needs.
8. Certain diuretics
Diuretics, or "water pills," that can lower your potassium levels can also interact with Qsymia. Examples include hydrochlorothiazide and furosemide (Lasix).
Qsymia can also lower potassium levels. So combining these medications may cause your potassium level to drop too low (hypokalemia). This can cause weakness, muscle cramps, or problems with your heartbeat in severe cases.
Your provider will likely check your potassium levels before and during treatment if you’re taking these medications together. But be sure to let them know if you’re having muscle cramps or feeling weaker than usual.
When should I contact my healthcare provider about a Qsymia interaction?
It’s best to catch any possible Qsymia interactions before they happen. Be sure your healthcare provider has a complete list of medications you take. Your list should include prescription and OTC medications, as well as supplements. This is especially important if you’re prescribed Qsymia by a different provider than the one you see for the rest of your health needs.
If you experience any unusual or bothersome side effects after starting Qsymia, let your provider know. They could be a sign of a drug interaction that needs to be addressed. If you need to stop taking Qsymia, they can help you taper your dose — stopping suddenly isn’t safe. For severe or life-threatening symptoms, seek emergency care right away.
The bottom line
Qsymia (phentermine / topiramate) interacts with birth control pills, alcohol, and CNS depressants. It can also interact with amitriptyline, diuretics, and some anti-seizure medications. You shouldn’t take Qsymia with MAOIs, and it’s best not to take it with other weight loss medications unless your healthcare provider OKs it.
Be sure your provider and pharmacist have an updated list of medications you take. They’ll be able to check for any interactions before you start taking Qsymia.
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References
Grunvald, E., et al. (2022). AGA clinical practice guideline on pharmacological interventions for adults with obesity. Gastroenterology.
Vivus LLC. (n.d.). Risk of birth defects with Qsymia.
Vivus LLC. (2023). Qsymia - phentermine and topiramate capsule, extended release [package insert].
Vivus LLC. (2023). Risk evaluation and mitigation strategy (REMS).
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