Femara (letrozole) is a prescription oral tablet that’s used to treat certain types of breast cancer. This drug can interact with other medications and some supplements. For example, Femara can interact with tamoxifen (Soltamox).
An interaction can occur because one substance causes another substance to have a different effect than expected. Interactions can also occur if you have certain health conditions.
Before you start taking Femara, tell your doctor and pharmacist about any prescription, over-the-counter, or other drugs you take. Sharing this information with them may help prevent possible interactions. (To learn whether Femara interacts with herbs or vitamins and supplements, see the “Are there other interactions with Femara?” section below.)
If you have questions about drug interactions that may affect you, talk with your doctor or pharmacist.
The table below lists drugs that may interact with Femara. Keep in mind that this table does not include all drugs that may interact with Femara. For more information about some of these interactions, see the “Drug interactions explained” section below.
Certain health conditions or other factors could raise your risk of harm if you take Femara. In such cases, your doctor may not prescribe Femara for you. These are known as contraindications. The list below includes Femara (letrozole) contraindications.
If you’re pregnant: If you’re pregnant, your doctor likely won’t prescribe Femara for you. This is because taking the drug during pregnancy could cause harm to a fetus.
If you can become pregnant, you’ll need to use birth control while you’re taking Femara and for at least 3 weeks after your last dose.
If you’ve had an allergic reaction: If you’ve had an allergic reaction to Femara or any of its ingredients, your doctor likely won’t prescribe Femara for you. This is because taking the drug could cause another allergic reaction. You can ask your doctor about other treatments that may be better options for you.
Before you start taking Femara, talk with your doctor if any of the factors above apply to you. Your doctor can determine whether Femara is safe for you to take.
Femara is not known to interact with alcohol. But Femara and alcohol can cause some similar side effects, such as headache, dizziness, and flushing. So, you may be more likely to experience these side effects if you drink alcohol during your Femara treatment.
If you have questions about consuming alcohol while taking Femara, talk with your doctor or pharmacist.
Learn more about certain drug interactions that can occur with Femara.
Interaction with tamoxifen
Femara can interact with tamoxifen (Soltamox). Femara and tamoxifen are both used to treat breast cancer.
What could happen
Taking Femara with tamoxifen can lead to a lower level of Femara in your body. This could make Femara less effective.
What you can do
If you take tamoxifen, talk with your doctor. They may not prescribe Femara with tamoxifen. However, your doctor may prescribe Femara after you stop taking tamoxifen.
If you have questions about taking Femara with tamoxifen, talk with your doctor or pharmacist.
Interaction with prasterone
Femara can interact with prasterone (Intrarosa), which is used to treat painful sex after menopause.
What could happen
Your body breaks down prasterone into certain hormones, including estrogen. Femara works by lowering the estrogen level in your body. So, taking these medications together could make either drug less effective.
What you can do
If you take prasterone, talk with your doctor. They likely won’t prescribe Femara with prasterone and can recommend other treatment options instead.
If you have questions about taking Femara with prasterone, talk with your doctor or pharmacist.
Interaction with estrogen
Femara can interact with estrogen (Menest, Premarin, others). Estrogen can be used for hormone replacement therapy after menopause and for other purposes.
What could happen
Femara works by lowering the level of estrogen in your body. Taking the drug with estrogen could make Femara less effective.
Femara is used to treat breast cancer; taking estrogen could promote the growth of breast cancer, making it less effective.
What you can do
If you take estrogen, talk with your doctor. They likely won’t prescribe Femara with estrogen. Your doctor can recommend alternatives to either drug.
If you have questions, talk with your doctor or pharmacist.
Femara may have other interactions. They could occur with supplements, foods, vaccines, or even lab tests. See below for details. Note that the information below does not include all other possible interactions with Femara.
Does Femara interact with supplements?
Femara may interact with dehydroepiandrosterone (DHEA) supplements, which are used for vaginal atrophy and other conditions. Taking Femara with DHEA supplements could make both of these less effective. Your doctor can recommend an alternative that isn’t known to interact with Femara.
Before you start taking Femara, talk with your doctor and pharmacist about any herbs, vitamins, and supplements you take. Sharing this information with them may help you avoid possible interactions.
If you have questions about interactions that may affect you, talk with your doctor or pharmacist.
Femara and herbs
There are currently no reports of Femara interacting with herbs. But this doesn’t mean that interactions with herbs won’t be recognized in the future.
For this reason, it’s still important to check with your doctor or pharmacist before taking any of these products while taking Femara.
Femara and vitamins
There are currently no reports of Femara interacting with vitamins. But this doesn’t mean that vitamin interactions won’t be recognized in the future.
For this reason, it’s still important to check with your doctor or pharmacist before taking any of these products while taking Femara.
Does Femara interact with food?
There are currently no reports of Femara interacting with food. If you have questions about eating certain foods during your treatment with Femara, talk with your doctor.
Does Femara interact with vaccines or lab tests?
There are currently no reports of Femara interacting with vaccines or lab tests. If you have questions about receiving certain vaccines or having lab tests done during your Femara treatment, talk with your doctor.
Does Femara interact with cannabis or CBD?There are currently no reports of Femara interacting with cannabis (commonly called marijuana) or cannabis products such as cannabidiol (CBD). But as with any drug or supplement, talk with your doctor before using cannabis with Femara.
Note: Cannabis is illegal at a federal level but is legal in many states to varying degrees.
Certain medical conditions or other health factors may raise the risk of interactions with Femara. Before taking Femara, talk with your doctor about your health history. They’ll determine whether Femara is right for you.
Health conditions or other factors that might interact with Femara include:
Osteoporosis: If you have osteoporosis, talk with your doctor before taking Femara. The drug may cause weakened bones, which could worsen your condition. Your doctor can determine whether Femara is a safe treatment option for you.
High cholesterol: If you have high cholesterol, talk with your doctor before starting Femara treatment. The drug could raise your cholesterol levels, which could make your condition worse. Your doctor can tell you whether Femara is safe for you to take.
Liver problems: If you have a liver problem, such as liver failure, talk with your doctor before taking Femara. Having a liver problem could raise the level of Femara in your system. This may increase your risk of side effects. Your doctor may prescribe a lower Femara dosage to help reduce this risk.
Pregnancy: It’s not safe to take Femara during pregnancy. To learn more, see the “When should I avoid Femara?” section above.
Breastfeeding: It’s not known whether Femara is safe to take while breastfeeding or whether it passes into breast milk. But because of the risk of serious side effects, breastfeeding is not recommended while you’re taking Femara or for 3 weeks after your last dose.
If you’re breastfeeding or planning to do so, talk with your doctor about your options.
Allergic reaction: If you’ve had an allergic reaction to Femara or any of its ingredients, your doctor will likely not prescribe Femara. This is because taking the drug could cause another allergic reaction. You can ask your doctor about other treatments that may be better choices for you.
Taking certain steps can help you avoid interactions with Femara. Before starting treatment, talk with your doctor and pharmacist. Things to discuss with them include:
- whether you drink alcohol or use cannabis
- other medications you take, as well as any vitamins, supplements, and herbs (they can also help you fill out a
medication list ) - what to do if you start taking a new drug during your Femara treatment
It’s also important to understand Femara’s
If you have difficulty reading or understanding this information, your doctor or pharmacist can help.
Taking Femara exactly as prescribed can also help prevent interactions.
Disclaimer: Healthline 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.