Key takeaways:
Qsymia (phentermine / topiramate ER) is an FDA-approved weight-loss medication. Qsymia interactions include amitriptyline, certain diuretics (water pills), 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 avoid alcohol and sedating medications while taking 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.
Qsymia (phentermine / topiramate ER) 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 works best when combined with regular exercise and a balanced diet.
Like other medications, Qsymia also has interactions to be aware of when you’re taking it. Knowing about Qsymia interactions can help you avoid unwanted side effects and other issues.
Qsymia interactions at a glance
Below is a list of possible Qsymia interactions to be aware of. Keep in mind that this isn’t a complete list — your prescriber or pharmacist can review your medication list for any other interactions that may apply to you.
Qsymia interactions include:
Birth control pills
Alcohol
Opioid pain medications, such as oxycodone (Roxicodone)
Benzodiazepines, such as alprazolam (Xanax)
Medications that cause drowsiness
Other weight-loss medications
Amitriptyline
Monoamine oxidase inhibitors (MAOIs), such as selegiline (Zelapar, Emsam)
Some anti-seizure medications, such as carbamazepine (Tegretol) and valproic acid (Depakote)
Some diuretics (water pills), such as hydrochlorothiazide (Microzide) and furosemide (Lasix)
Carbonic anhydrase inhibitors, such as a acetazolamide
Pioglitazone (Actos)
Let’s take a closer look at eight Qsymia interactions you should know about.
1. Birth control pills
Oral contraceptive pills (birth control pills) interact with Qsymia. Qsymia may lower the levels of birth control hormones in the body. This 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 prescriber know if it’s happening often. They may recommend a different form of birth control for you.
If you’re taking birth control pills to prevent pregnancy, an additional birth control method is required while you’re taking Qsymia. This is because Qsymia can cause serious fetal harm if you become pregnant while taking it. And this interaction could make birth control pills less reliable, especially if you forget to take one now and then. 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 also interacts 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.
The phentermine component of Qsymia can also make you more sensitive to alcohol. This can increase the risk of unwanted intoxication and alcohol-induced harm. Plus, alcohol can interfere with your weight-management goals.
With this in mind, it’s best to limit or avoid alcohol consumption while taking Qsymia. If you drink alcohol regularly, let your prescriber know before starting Qsymia. They can help you safely reduce your alcohol intake. Or they may recommend a different weight-loss medication that’s safer 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.
Real stories: Wonder what it’s like to take Qsymia (phentermine / topiramate ER) for weight loss? Read these first-hand accounts from people taking Qsymia.
When will Qsymia start working? Expert answers to this and more FAQs about Qsymia.
Qsymia vs. Wegovy: Here’s how these two weight-loss medications compare.
3. Sedatives
Central nervous system (CNS) depressants, or sedatives, are medications that slow down brain activity. They include:
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 prescriber 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 prescriber 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, Lomaira) 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 use.
Taking Qsymia with another medication that contains the same ingredient isn’t recommended, as it can increase side effects and may be harmful to your health.
Can you 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 well 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 prescriber 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 prescriber 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. This can raise the risk of amitriptyline side effects, such as dry mouth and constipation.
Your prescriber 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)
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 life-threatening 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 prescriber can recommend 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 and phenytoin (Dilantin) can lower Qsymia levels in the body, which can make it less effective.
Valproic acid 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 prescriber 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.
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 prescriber will likely check your potassium levels before and during treatment if you’re taking Qsymia and a diuretic together. But be sure to let them know if you’re having muscle cramps or feeling weaker than usual.
Frequently asked questions
Yes, you can take Qsymia and vitamin D together. There isn’t a direct interaction between them, so it’s likely fine if your prescriber recommends it. However, taking more vitamin D than recommended can increase your risk of developing kidney stones. Qsymia also has this risk, so the combination could make the chance of kidney stones more likely. It’s best to avoid taking extra vitamin D unless your prescriber recommends it.
It’s possible that Qsymia can cause or worsen anxiety for some people. This may be due to phentermine’s stimulant effects. In this case, anxiety typically improves as your body adjusts to Qsymia. But the topiramate component of Qsymia can cause more long-lasting mood changes for some people. If you notice feelings of anxiety or other mood changes that aren’t improving while taking Qsymia, let your prescriber know. A different weight-loss medication may be a better option for you.
It’s best to get an OK from your prescriber before taking melatonin with Qsymia. The combination could increase the risk for excessive drowsiness and other side effects. Keep in mind that Qsymia itself can cause insomnia for some people. Taking it first thing in the morning can help prevent this side effect. But if insomnia becomes a problem, your prescriber can help you find a safe treatment option.
Yes, you can take Qsymia and vitamin D together. There isn’t a direct interaction between them, so it’s likely fine if your prescriber recommends it. However, taking more vitamin D than recommended can increase your risk of developing kidney stones. Qsymia also has this risk, so the combination could make the chance of kidney stones more likely. It’s best to avoid taking extra vitamin D unless your prescriber recommends it.
It’s possible that Qsymia can cause or worsen anxiety for some people. This may be due to phentermine’s stimulant effects. In this case, anxiety typically improves as your body adjusts to Qsymia. But the topiramate component of Qsymia can cause more long-lasting mood changes for some people. If you notice feelings of anxiety or other mood changes that aren’t improving while taking Qsymia, let your prescriber know. A different weight-loss medication may be a better option for you.
It’s best to get an OK from your prescriber before taking melatonin with Qsymia. The combination could increase the risk for excessive drowsiness and other side effects. Keep in mind that Qsymia itself can cause insomnia for some people. Taking it first thing in the morning can help prevent this side effect. But if insomnia becomes a problem, your prescriber can help you find a safe treatment option.
The bottom line
Qsymia (phentermine / topiramate ER) interacts with birth control pills, alcohol, and sedating medications. It can also interact with amitriptyline, diuretics (water pills), and some anti-seizure medications. You shouldn’t take Qsymia with monoamine oxidase inhibitors (MAOIs), and it’s best not to take it with other weight-loss medications unless your prescriber OKs it.
Be sure your prescriber 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.
Letevernier, E., et al. (2018). Vitamin D, hypercalciuria and kidney stones. Nutrients.
Qsymia. (n.d.). Risk evaluation and mitigation strategy (REMS).
Qsymia. (n.d.). Risk of birth defects with Qsymia.
Teva Pharmaceuticals. (2025). Phentermine and topiramate- phentermine and topiramate capsule, extended release [package insert].
