If you’ve been prescribed letrozole (Femara) to help prevent your breast cancer from returning, it’s good to be aware of all potential side effects. Insomnia (persistent trouble sleeping) is one side effect that several MyBCTeam members have reported experiencing while taking letrozole.

One member asked, “I’ve been taking letrozole in the evening, and now I have insomnia. Does anyone take it in the morning? Do you sleep well?”

Since letrozole is usually taken long term, you’ll likely be taking it for several years. In this article, we’ll explore the ways that letrozole can cause sleep problems, and we’ll provide insights on managing this side effect.

What Is Letrozole?

Some types of breast cancer respond to hormones in your body, such as estrogen. These types are called estrogen receptor-positive (ER-positive) cancers. Letrozole and other aromatase inhibitors, such as exemestane (Aromasin) and anastrozole (Arimidex), limit the amount of estrogen your body makes, thereby decreasing the risk of ER-positive cancer from recurring (returning).

After you complete initial breast cancer treatment — such as radiotherapy, chemotherapy, or surgery — your doctor may prescribe hormonal therapy to keep your cancer in remission (periods when signs and symptoms have decreased or disappeared).

While limiting estrogen levels may help keep hormone receptor-positive cancer in remission, lower estrogen levels can cause a wide range of menopausal symptoms and side effects. A few common side effects of letrozole include:

• Pain
• Hot flashes
• Osteoporosis (decreased bone density)
• Fatigue (tiredness)
• Hypercholesterolemia (high cholesterol)

Read more about side effects of hormonal therapy.

Letrozole Can Interfere With Sleep

Letrozole and other medications used in hormonal therapy can interfere with your sleep patterns, including causing the sleep disorder insomnia — difficulty falling or staying asleep. In clinical trials including letrozole, 7.8 percent of participants — all postmenopausal women with HR-positive and node-positive early-stage breast cancer — experienced insomnia as a side effect.

Side Effects of Letrozole That Can Disrupt Sleep

In addition to disrupting your sleep patterns directly, letrozole has some other potential side effects that can make sleeping more difficult. These side effects include:

• Pain — Letrozole can cause pain throughout your body, which may make both finding a comfortable sleep position and falling asleep difficult.
• Urinary problems — Letrozole may make you urinate more frequently, which can wake you up in the middle of the night.
• Hot flashes — Letrozole can interfere with your body’s ability to regulate its temperature, which can cause night sweats that wake you up at night.
• Depression and nervousness — Letrozole can impact your mental health, making it hard to relax at night.
• Cough — Frequent coughing can make it difficult to fall asleep or may wake you up in the night.
• Dizziness or lightheadedness — Letrozole can upset your sense of balance and make lying down uncomfortable.
• Nausea — Feeling like you’re going to vomit can be incredibly disruptive to sleep.
• Troubled breathing — Difficulty breathing can cause anxiety and disturb your sleep.

Other Potential Causes of Insomnia

Insomnia is common among people with breast cancer, including those who aren’t currently taking letrozole. Pain or hot flashes caused by breast cancer, stress, and other medications can all contribute to your inability to sleep.

Managing Sleep Disturbances

A lack of sleep can have far-reaching impacts on your health and quality of life. There are several strategies that you can use to cope with your insomnia.

Create a Sleep Routine

Establishing a consistent sleep routine can improve your sleep quality. Going to bed at the same time every night helps regulate your body’s internal clock and promotes a natural sleep-wake cycle.

Avoid napping or sleeping during the day, as it can disrupt your sleep pattern. If you’re having trouble falling asleep, refrain from lying in bed for more than 20 minutes. Instead, engage in relaxing activities like reading or listening to soft music until you feel drowsy.

To optimize your sleep environment, ensure your bedroom is dark, cool, and quiet. Consider using blackout curtains, adjusting the temperature, and minimizing external noises. Playing white noise or calming sounds, like a gentle river, can also aid in falling asleep.

Avoid screens, such as smartphones or laptops, before bedtime, as the blue light they emit can interfere with sleep. Instead, engage in calming activities like yoga, deep breathing exercises, or reading to unwind and prepare your body for a restful night’s sleep.

Find the Right Sleep Aid

If you’re struggling with persistent insomnia, you may consider adding sleep aids and medications to your treatment plan. There are various types of sleep aids available, including over-the-counter sleep aids, prescription medications, and natural supplements like melatonin.

Always consult with your health care provider before starting any new medication or supplement, as these drugs could interfere with how letrozole works or worsen other side effects. Your doctor can help you choose a safe sleep aid.

Make Exercise a Priority

Giving your body a reason to be tired is an effective approach to combating insomnia. Engaging in regular physical activity can provide numerous benefits in addition to helping you sleep. Exercise helps boost energy levels, making you feel more tired by the end of the day. It also helps reduce stress and anxiety, which are common causes of sleep disturbances. Research has also linked engaging in regular physical activity with better survival rates and lower chances of recurrence in women diagnosed with high-risk breast cancer, according to the National Cancer Institute.

Find Ways To Cope With Night Sweats

Coping with night sweats can be challenging, but there are several techniques that can help provide relief.

Keep Cool

One effective strategy is to use cooling techniques such as setting your thermostat lower at night, opting for lightweight bedding and sleepwear, using fans, or trying cooling bedding. One MyBCTeam member said of their cooling blanket, “I call it my magic blanket — it’s about 10 degrees cooler on one side than the other.”

Sleep on a Towel

Another helpful tip is to sleep on a towel or moisture-wicking blanket, which can absorb excess moisture and help you stay dry throughout the night. You can also easily refresh your bed if you wake up sweaty by changing out the towel.

Take a Shower

If you wake up drenched in sweat, a quick shower can help warm you up and make falling back to sleep easier.

Treat Hot Flashes

Your doctor may add medications to help treat hot flashes. One MyBCTeam member reported improvements in hot flashes while taking the antidepressant venlafaxine (Effexor), saying, “The first month on letrozole, I had hot flashes once or twice a day, but mostly at night. After a month, they gradually stopped, and within two months I rarely had them. I also started taking Effexor for anxiety about two weeks before starting letrozole. My oncologist mentioned that Effexor helps lessen hot flashes.”

Talk With Your Health Care Providers

If you’ve tried managing your insomnia yourself and can’t seem to find relief, it’s probably time to talk with your doctor. They may be able to adjust your dose or recommend that you take letrozole at a different time during the day to reduce the medication’s impact on your sleep.

“I take letrozole first thing in the morning,” said one MyBCTeam member. “I had to do that so I could sleep. It made a big difference.”

Always get medical advice before making any changes to the way you take your medications.

Talk With Others Who Understand

On MyBCTeam — the social network for people with breast cancer and their loved ones — more than 64,000 members come together to ask questions, give advice, and share their stories with others who understand life with breast cancer.

Have you experienced insomnia while taking letrozole? Do you have any tips for getting better sleep? Share your experience in the comments below, or start a conversation by posting on your Activities page.