Key takeaways:
Letrozole (Femara) is a medication that treats breast cancer and certain types of infertility.
Common letrozole side effects include hot flashes, nausea, and fatigue. High cholesterol, joint pain, and bone loss are also possible.
More serious side effects are rare, but possible. They include bone fractures and complications from high cholesterol. It’s important to keep up with regular screenings for bone loss and cholesterol changes while taking letrozole.
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Letrozole (Femara) is a medication that treats certain types of estrogen-sensitive breast cancer. It’s also often prescribed off-label for certain types of infertility.
Like most medications, letrozole has side effects you should be aware of. Some letrozole side effects are mild and improve over time. But others may require medical attention. Knowing what to expect — and how to manage your symptoms — can help you feel more prepared during treatment. Here’s what you should know.
Letrozole side effects at a glance
Below is a list of common and rare but serious letrozole side effects. Keep in mind that this isn’t a complete list of all possible side effects. Don’t hesitate to reach out to your healthcare team about any side effects that occur while taking letrozole, even if they aren’t listed below.
Common and mild letrozole side effects include:
Hot flashes
Night sweats
Increased cholesterol levels
Joint, muscle, and bone pain
Nausea or vomiting
Fatigue
Weakness
Abdominal bloating and cramps (more likely when treating infertility)
Edema (fluid retention and swelling)
Headache
Dizziness
Vaginal dryness or irritation
Weight changes
Insomnia
Constipation
Diarrhea
Hair loss
Mood changes
More serious letrozole side effects and risks may include:
Decreased bone density and increased risk of fractures
Allergic reactions
Let’s take a closer look at seven letrozole side effects and what to do if they occur.
1. Hot flashes and night sweats
Letrozole blocks an enzyme (protein) called aromatase. This enzyme changes androgen hormones (like testosterone) found in skin, muscle, and fat cells into estrogen. Blocking aromatase lowers estrogen levels in the body.
Low estrogen levels can lead to menopause-like symptoms, such as hot flashes and night sweats. Vaginal dryness and irritation is also possible. These letrozole side effects may be annoying, but they’re not dangerous.
Lifestyle changes — like exercising and eating more fruits and veggies — may help reduce hot flashes. Some people find that mindfulness practices, such as yoga and meditation, are also useful. Over-the-counter (OTC) vaginal lubricants can help with dryness and irritation.
You should avoid natural supplements for hot flashes or night sweats unless your prescriber OKs them. Many of these OTC products contain plant-based estrogens, known as phytoestrogens. Phytoestrogens act like estrogen in the body. So while they might improve hot flashes, they could interfere with how letrozole works.
2. Fatigue
Fatigue is another common letrozole side effect. You may feel weaker or more tired than usual while taking it. Dizziness is also possible.
Use caution when driving or operating machinery until you know how letrozole affects you. To help combat fatigue, do your best to stay hydrated and choose energy-boosting foods, such as berries and leafy greens. Regular exercise can also help, if you’re able. But if fatigue becomes severe or bothersome, speak with your healthcare team for guidance.
3. High cholesterol
High cholesterol is a common letrozole side effect. In many cases, the change is mild and won’t require treatment. But if your cholesterol becomes too high, and you aren’t able to manage it with diet and exercise changes, your prescriber may recommend a medication to help lower it. That’s because if they’re left untreated, high cholesterol levels can raise your risk of serious complications, such as a heart attack or stroke.
Your prescriber will likely check your cholesterol levels before and during treatment with letrozole. Staying on top of your appointments can help your healthcare team identify and manage this side effect promptly if it occurs.
4. Nausea
Nausea is a common side effect of many medications, including letrozole. You can take it with or without food. But if letrozole is causing nausea, taking it with food may help. It’s also a good idea to stay hydrated and eat smaller, more frequent meals.
5. Fluid retention
Letrozole can sometimes cause swelling due to excess fluid in your body. You’ll likely notice this in your hands, feet, and ankles. If you’re taking letrozole for fertility, you may also feel bloated or notice swelling in your abdomen.
In most cases, this side effect is minor and may improve as your body adjusts to letrozole or after you stop taking it. In the meantime, elevating your legs or going for a walk can help. But if swelling persists or is severe, seek medical care.
6. Muscle and joint pain
Muscle and joint pain can happen while taking letrozole. This letrozole side effect is also known as aromatase-inhibitor associated arthralgia. It’s unclear exactly why muscle and joint pain happen. But it’s likely related to bone loss and inflammation that can occur when estrogen levels drop.
If you have joint pain while taking letrozole, an OTC pain medication, such as ibuprofen (Advil, Motrin) or naproxen (Aleve), may help. Just make sure to OK it with your prescriber first. If pain becomes severe or is interfering with your daily life, let your healthcare team know. A different medication may be a better option for you.
7. Bone loss and fractures
Because letrozole lowers estrogen levels, it can cause bone loss as a side effect. Over time, this can raise the risk of osteoporosis and fractures (broken bones).
A scan to check your bone density is typically recommended before starting and while taking letrozole. Your prescriber may also recommend taking calcium with vitamin D or a medication called Prolia (denosumab) to strengthen your bones.
Seek emergency care if you notice signs or symptoms of a fracture, such as sudden pain, swelling, or trouble moving a limb.
Good to know: Bone loss isn’t typically an issue if you’re taking letrozole for infertility. That’s because in most cases you’ll only take it for a few days of your cycle. So it doesn’t stay in your system long enough to significantly affect your bone density.
Frequently asked questions
It’s a good idea to avoid alcohol and high-fat foods while taking letrozole. Consuming these things can make high cholesterol levels even more likely. It’s also best to avoid soy-based supplements or powders. They may interfere with letrozole’s effectiveness.
It’s possible. Letrozole lowers estrogen levels. In turn, decreased estrogen may lead to dry skin and wrinkles. This is because estrogen helps maintain your skin moisture, collagen level, and elasticity. Using sunscreen and moisturizer daily can help protect your skin. You can also talk to a dermatologist about other treatment options. Just be sure to avoid any hormone-based treatments — they may interfere with letrozole’s effectiveness.
Eye problems are possible while taking letrozole, but they aren’t common. Still, if you notice blurred vision or other changes in your eyesight while taking letrozole, it’s best to have your eyes checked by a medical professional. They can determine the cause and best next steps to manage your symptoms.
It’s a good idea to avoid alcohol and high-fat foods while taking letrozole. Consuming these things can make high cholesterol levels even more likely. It’s also best to avoid soy-based supplements or powders. They may interfere with letrozole’s effectiveness.
It’s possible. Letrozole lowers estrogen levels. In turn, decreased estrogen may lead to dry skin and wrinkles. This is because estrogen helps maintain your skin moisture, collagen level, and elasticity. Using sunscreen and moisturizer daily can help protect your skin. You can also talk to a dermatologist about other treatment options. Just be sure to avoid any hormone-based treatments — they may interfere with letrozole’s effectiveness.
Eye problems are possible while taking letrozole, but they aren’t common. Still, if you notice blurred vision or other changes in your eyesight while taking letrozole, it’s best to have your eyes checked by a medical professional. They can determine the cause and best next steps to manage your symptoms.
The bottom line
Letrozole (Femara) is a medication that treats breast cancer and infertility. Common letrozole side effects include hot flashes, nausea, and fatigue. These side effects can often be managed with lifestyle changes. High cholesterol, joint pain, and bone loss are also possible.
More serious letrozole side effects include bone fractures and complications from high cholesterol. Follow up with your prescriber to get regular screenings for bone loss and cholesterol changes while taking letrozole. And reach out to them if you experience any side effects that worsen or interfere with your daily life.
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