This article describes possible interactions with phentermine oral tablet. Interactions can cause a drug to have a different effect on the body than expected. Interactions can occur due to medications, alcohol, or certain health conditions.
Phentermine comes as tablets and capsules that you’ll swallow. It’s also available as a tablet that dissolves in your mouth.
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Other drugs and phentermine
The drugs in the list below may interact with phentermine oral tablet. This article doesn’t include all drugs that may interact with phentermine.
Drug classes or drugs that may interact with phentermine oral tablet include:
- alpha-blockers, when used for high blood pressure:
- drug examples: terazosin, prazosin (Minipress)
- what might happen: can make the alpha-blocker less effective at lowering blood pressure
- diabetes medications:
- drug examples: metformin (Fortamet, Glumetza), canagliflozin (Invokana)
- what might happen: can make the diabetes medication less effective
- beta-blockers:
- drug examples: metoprolol (Lopressor, Toprol XL), carvedilol (Coreg)
- what might happen: can make the beta-blocker less effective
- ergot alkaloids:
- insulins:
- drug examples: insulin glargine (Basaglar), insulin lispro (Admelog)
- what might happen: can make the insulin medication less effective
- stimulants:
- monoamine oxidase inhibitors (MAOIs):*
- drug examples: phenelzine (Nardil), linezolid (Zyvox)
- what might happen: increases the risk of serious side effects of the MAOIs and phentermine
- esketamine (Spravato):
- what might happen: can increase the risk of side effects of phentermine and esketamine
- midodrine (Orvaten):
- what might happen: can increase the risk of side effects of phentermine and midodrine
- riociguat (Adempas):
- what might happen: can increase the risk of side effects of phentermine and riociguat
* For more details about this interaction, see the “When to avoid phentermine” section below.
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Health factors and phentermine
Certain medical conditions or other health factors may increase the risk of interactions with phentermine oral tablet. Keep in mind that interactions could lead to side effects or affect how well the drug works. Before taking phentermine, tell your doctor about your health history. They’ll discuss any phentermine warnings with you and help determine whether phentermine is right for you.
These health conditions or other factors might interact with phentermine oral tablet:
When to avoid phentermine
Certain health conditions or other factors could increase some risks with phentermine oral tablet. Because of this, doctors may not prescribe phentermine in these cases. These health conditions or other factors are called contraindications.
Here’s a list of contraindications for phentermine oral tablet:
- Heart disease: If you have heart disease, you have a higher risk of serious side effects from taking phentermine. Examples of heart disease include heart failure, coronary artery disease, and past stroke.
- Overactive thyroid: If you have an overactive thyroid taking phentermine oral tablet may worsen your condition.
- Glaucoma: If you have glaucoma, taking phentermine oral tablet may worsen your condition.
- History of a substance use disorder: Phentermine has potential for misuse, and doctors typically won’t prescribe it if you have a history of a substance use disorder. (With misuse, a drug is taken in a way other than how a doctor prescribes it.)
- Pregnant or breastfeeding: Phentermine should not be taken during pregnancy or breastfeeding due to the risk of harm.
- Current or recent use of an MAOI drug: If you take or have taken an MAOI within the past 14 days, taking phentermine oral tablet may cause dangerously high blood pressure.
- Past allergic reaction to phentermine: If you’ve ever had an allergic reaction to phentermine oral tablet, taking it again may cause another allergic reaction.
Before you start taking phentermine, tell your doctor if anything listed above relates to you. They can recommend whether you should take phentermine.
Other interactions and phentermine
Interactions can occur with supplements, foods, vaccines, and some lab tests. Below you can learn whether phentermine oral tablet has these interactions.
The information below doesn’t include all other possible interactions with phentermine.
Phentermine and supplements
Before taking phentermine oral tablet, tell your doctor and pharmacist about any herbs you take, as well as vitamins and supplements. Doing so may help you avoid interactions.
In addition to the interactions below, phentermine interacts with supplements that contain caffeine, such as certain pre-workout supplements. Consuming caffeine while taking phentermine can increase the risk of side effects, including high blood pressure.
If you have questions about interactions that may affect you, talk with your doctor or pharmacist.
Phentermine interactions with vitamins
Phentermine oral tablet isn’t known to interact with any vitamins. But this doesn’t mean interactions with vitamins can’t happen or won’t be identified later.
Because of this, ask your doctor or pharmacist before taking any of these products while taking phentermine oral tablet.
Phentermine interactions with herbs
Phentermine oral tablet may interact with St. John’s wort. This herb is often used to support mood and ease symptoms of depression.
Taking phentermine and St. John’s wort may increase your risk of serotonin syndrome as a side effect. (With serotonin syndrome, you have high levels of serotonin in your body, which may cause serious side effects.)
Because of this, ask your doctor or pharmacist before taking any of these products while taking phentermine oral tablet.
Phentermine and food
Phentermine interacts with food or drinks that contain caffeine, including coffee, green tea, and chocolate. Consuming caffeine while taking phentermine can increase the risk of side effects, including high blood pressure.
Because of this, talk with your doctor or pharmacist about what foods you should avoid while taking phentermine oral tablet.
Phentermine and vaccines
Phentermine oral tablet isn’t known to interact with any vaccines. But this doesn’t mean interactions with vaccines can’t happen or won’t be identified later.
Because of this, talk with your doctor or pharmacist before receiving any vaccines while taking phentermine oral tablet.
Phentermine and lab tests
Phentermine oral tablet isn’t known to interact with lab tests. But this doesn’t mean interactions with lab tests can’t happen or won’t be identified later.
Because of this, talk with your doctor or pharmacist before having any tests while taking phentermine oral tablet.
Phentermine and cannabis or CBD
Phentermine oral tablet isn’t known to interact with cannabis (commonly called marijuana) or cannabis products such as cannabidiol (CBD). But this doesn’t mean interactions can’t happen or won’t be identified later.
As with any drug or supplement, tell your doctor before taking cannabis with phentermine.
Note: Cannabis is illegal at a federal level but is legal in many states to varying degrees.
Alcohol and phentermine
Phentermine oral tablet is known to interact with alcohol.
Taking phentermine oral tablet and drinking alcohol may increase your risk of side effects from phentermine.
If you drink alcohol, talk with your doctor about whether it’s safe to consume it while taking phentermine oral tablet. They can provide more information about phentermine interactions with alcohol.
Preventing phentermine interactions
You may be able to help avoid certain interactions with phentermine oral tablet. Before taking this drug, you may want to discuss possible interactions with your doctor and pharmacist.
Things to consider include:
- Whether you drink alcohol or use cannabis.
- Other medications and herbs you take, as well as vitamins and supplements. Your doctor or pharmacist can help you fill out a medication list.
- What to do if you’re prescribed a new drug while taking phentermine oral tablet.
Taking phentermine exactly as prescribed can also help prevent interactions.
What to ask your doctor
If you have questions about phentermine and possible interactions, talk with your doctor.
Questions you may want to ask your doctor include:
- Do I need to take my medications at different times throughout the day to avoid interactions?
- Do other drugs that could treat my condition have similar interactions?
- Should I let you know if I make lifestyle changes, such as to my diet or exercise routine?
- If I have diabetes and I’m prescribed phentermine, would you be changing the dosage of my diabetes medication?
- What blood pressure medications are safe to take together with phentermine?
Disclaimer: Optum Perks has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.
