Does Letrozole cause weight gain?

Does Letrozole cause weight gain?

Medically reviewed by Dr. Doug Blayney on March 10, 2023


The term "breast cancer" is frequently mentioned, but it's important to remember that there are various types of this condition. In the United States and many Western countries, the predominant form is known as hormone-positive or estrogen receptor-positive breast cancer. This particular type of breast cancer depends on hormones such as estrogen and progesterone to send signals that prompt the growth of cancer cells. Healthcare professionals combat hormone-positive breast cancer by employing hormone therapies designed to impede the influence of these hormones, thereby decelerating or halting the cancer's progression.

Letrozole is one of these types of “hormone blocking” medicines for breast cancer that can lower the chance of it coming back and spreading. There are two other medications which work like letrozole: Anastrozole and exemestane.  All three are very similar in their anti cancer benefit and the way in which they work. All three are  taken as a pill every day and work by protecting the cancer cells from the estrogen signaling growth signal. Letrozole clogs up the body’s mechanism for manufacturing estrogen, and removing the estrogen signaling from the body.  Like many medicines, letrozole has side effects. One of the more annoying day-to-day side effects of manipulating estrogen and progesterone signaling in other parts of the body is weight gain. And since Letrozole is typically given to women who are postmenopausal, this weight gain can come on top of that other contributor to weight gain. We will talk more about that below.

Table of Contents - Does Letrozole cause weight Gain

Understanding Letrozole

Let’s dive into what letrozole is and how it’s used to treat hormone-positive breast cancer. Also, as we’ve mentioned in prior articles, let’s pause for a moment to acknowledge that so many cancer drug names sound like they could be a Star Wars character… thank you to our friend Matthew Rosenblum for calling this out in one of our Patient from Hell podcast episodes, and now we can’t unsee this odd (but accurate!) association! 

What is Letrozole?

Letrozole is an important medication in the fight against breast cancer. Specifically, it belongs to a group of medicines called aromatase inhibitors (the other aromatase inhibitors are anastrozole and exemestane). Aromatase inhibitors are medicines commonly used in women who have gone through menopause. These medications help block the production of estrogen, a hormone that can fuel certain types of breast cancers in postmenopausal women.

How Letrozole works?

Letrozole helps by blocking the production of estrogen, which slows down or even stops the cancer cells from spreading. In simpler terms, it's like putting a brake on something that helps cancer grow.

Why is this medication prescribed?

So, when doctors prescribe Letrozole, they're using it as a tool to fight breast cancer by disrupting the hormone support that these cancer cells depend on for their growth. This study shows why aromatase inhibitors are typically more effective in postmenopausal women if you want more info.

Estrogen is made in several organs in the body. The ovary is the largest source of estrogen in premenopausal women. The other sources of estrogen manufacture in both women and men are fat cells and the breast.   In premenopausal women, the aromatase inhibitors are not strong enough to prevent estrogen manufacture in the ovaries. When letrozole is used in premenopausal women, they are also treated with “ovarian suppression” – a medical term for inducing menopause – either with medications or by removing the ovaries. Goserelin is one medication to suppress the ovarian manufacture of estrogen. Goserolin also temporarily induces menopause. 

Aromotase inhibitors turn off estrogen manufacture in the body’s fat cells and in the breast tissue, and reduce estrogen levels to almost undetectable amounts. This effect occurs in both men and women. 

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Does Letrozole Cause Weight Gain?

This study done in 2016 looked at weight change in postmenopausal Stage I-III breast cancer (BC) survivors on tamoxifen or aromatase inhibitors (AI) [anastrozole, exemestane, letrozole]. The researchers found that in their sample, 27% had clinically significant weight loss and 37% weight gain within the first 2 years of using a hormone blocking medicine (ET). And we hear anecdotally from our community that weight gain is a common complaint. Because Letrozole is often prescribed for women who have already gone through menopause, it is sometimes difficult to determine whether the weight gain is caused by the medication or by the natural reduction of hormones in the body during menopause. Regardless of the cause, it’s definitely a common complaint in our community.

Read more: Weight Gain while on Tamoxifen

Investigating the Side Effects of Letrozole

Like most drugs to treat cancer, letrozole has a number of side effects that you might experience. It’s always a bummer to know the drugs helping to treat cancer bring about their own set of problems. Thanks, Cancer.

Common Letrozole side effects

According to the National Cancer Institute (NCI), some of the common side effects of letrozole include:

  • Hot Flashes: Sudden feelings of warmth and sweating.
  • Joint Pain or Stiffness: Discomfort or difficulty moving in the joints.
  • Fatigue: Feeling extremely tired or lacking energy.
  • Increased Sweating: Experiencing more perspiration than usual.

Less common side effects of letrozole

The NCI lists the following side effects of letrozole as occurring in 4 to 20 out of 100 patients:

  • Fluid around lungs
  • Swelling of the liver which may cause belly pain
  • Constipation, diarrhea, nausea, vomiting, loss of appetite, heartburn
  • Loss of bone tissue, broken bone, or decreased height
  • Swelling of the body
  • Cloudiness of the eye, visual disturbances
  • Vaginal bleeding
  • Dizziness, headache
  • Difficulty sleeping
  • Worry, depression, nervousness, irritability, difficulty remembering things, mood swings
  • Hair thinning

Rare and serious side effects of letrozole

While less than 3 in 100 patients may have the following side effects per the NCI, it’s important to be aware and contact your healthcare team as soon as possible:

  • Heart attack or heart failure which may cause shortness of breath, swelling of ankles, and tiredness
  • Stroke which may cause weakness, paralysis
  • Blood clot which may cause swelling, pain, shortness of breath
  • Liver damage which may cause yellow eyes and skin
  • Allergic reaction which may cause rash, low blood pressure, wheezing, shortness of breath, swelling of the face or throat

Every person is different, so make sure you are actively communicating with your doctor and care team to report and manage your side effects. If you are like me, and forget the list of things to discuss with your doctor between appointments, check out our Manta Planner which helps you prepare for appointments, track your symptoms and write down questions for your doctor.

Managing Weight Gain and Other Side Effects

So what do you do about all this extra side effect crap you have to deal with?! We have a few suggestions here, but drop a comment below if there has been anything particularly helpful for you that we missed. 

Supportive Care for Managing Letrozole Side Effects

Palliative care is amazing for helping to manage side effects. Palliative care has gotten a bad rap over the years, as people automatically associate the word “palliative” with “hospice.” Palliative care is not exclusively end of life care. Hospice is the end-of-life version of palliative care, but palliative care can be used throughout your treatment experience. Palliative literally means supportive, so here are some supportive strategies for managing some of those side effects.

The joint pain and stiffness that are common with letrozole sometimes goes away by itself (that is “resolves spontaneously’).  If this is not the case, sometimes changing to another aromatase inhibitor sometimes solves the problem. In terms of anticancer efficacy, most oncologists agree that there is very little difference among the three drugs in this class.  Ask your oncologist if this concern arises.

And trust me, I wish I had a tried and true solution to the dilemma of weight gain while using Letrozole and other hormone blocking medicines. The truth is, there’s not one “silver bullet” answer to solve this. Here are some tips from our community for combatting weight gain… and don’t be annoyed that some of these are the old tried and true “diet and exercise” go-to’s. Trust me, it annoys me still because it’s really hard to deal with this on top of being worried about cancer – I get it! But regardless, here are those tips:

  1. Maintain a Healthy Diet: Focus on a balanced diet rich in fruits, vegetables, lean proteins, and whole grains to help control your weight. But even if you “slip up” every now and then, do not beat yourself up – everything in moderation… even treats now and then.
  2. Stay Active: Incorporate regular physical activity into your routine, such as walking, swimming, or other exercises you enjoy. Even a few minutes each day is better than nothing.
  3. Strength Training: Include strength training exercises to help build muscle, which can boost metabolism.
  4. Stay Hydrated: Drinking enough water can help you feel full and reduce the likelihood of overeating.
  5. Limit Sugary and High-Fat Foods: Minimize the consumption of sugary snacks and high-fat foods, which can contribute to weight gain. I promise we’re not trying to take all the fun out of your life… just remember the ‘ol “everything in moderation” phrase!
  6. Mindful Eating: Pay attention to hunger and fullness cues, and avoid emotional or stress eating. I found this to be difficult because… uh… cancer?! Can’t forget about that guy. And so be gentle with yourself if every now and then you partake in some emotional eating because… Cancer!
  7. Regular Check-Ins: Keep regular appointments with your healthcare provider to monitor your health and discuss any concerns about weight changes.
  8. Sleep Well: Aim for a consistent and adequate amount of sleep to support your metabolism and overall health.
  9. Support System: Share your feelings with friends and family who can provide encouragement and help you process the complex life that comes with a cancer diagnosis. It’s also a good idea to consider talking to a mental health professional. You’re dealing with a lot and it’s ok to ask for help.

Remember, it's essential to consult your healthcare provider before making significant changes to your diet or exercise routine, especially while taking Letrozole. They can provide personalized guidance and recommendations based on your individual needs and health.

Manta Care’s Holistic Support System

The Manta Cares team is made up of cancer patients, caregivers and survivors, and we have been dropped into Cancerland ourselves. We have felt that fear, sadness, anger and have also found the silver linings along the way. We work with amazing oncologists and cancer experts who help ensure that the information and resources we are providing for you are science-backed. 

Please don’t hesitate to reach out with any questions. Be sure to subscribe to our newsletter and check out our free resources like our Chemotherapy Checklist for Caregivers, Financial Checklist for Cancer Treatment and more. We also put out a bi-weekly podcast called the Patient from Hell to educate, empower and hopefully inspire you as you go through this crappy experience. You can listen on Spotify, Apple Podcasts, YouTube or anywhere you listen to podcasts. Dealing with cancer as a patient or caregiver can feel really lonely. Just know that you are not alone in this experience.

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In conclusion, breast cancer is not a singular entity but comprises various types, with hormone-positive or estrogen receptor-positive breast cancer being prevalent in the United States and many Western nations. This type of breast cancer relies on hormones like estrogen and progesterone to stimulate the growth of cancer cells, and healthcare professionals combat it using hormone therapies. Letrozole, an aromatase inhibitor, is a crucial medication in this fight, blocking estrogen production and slowing or stopping cancer cell growth. Despite its effectiveness, Letrozole, like many cancer treatments, comes with side effects. Notably, weight gain is a common concern, especially as it is often prescribed for postmenopausal women. Understanding and managing these side effects is crucial, and while no one-size-fits-all solution exists, maintaining a healthy lifestyle, seeking supportive care, and regular check-ins with healthcare providers are vital steps in navigating the complexities of breast cancer treatment and its associated challenges. Remember, each person's journey is unique, and open communication with healthcare teams ensures personalized care for the best outcomes. And the Manta Cares team is here to walk with you along the way!


What is letrozole used for?

Letrozole is used to treat breast cancer in women, especially after menopause. It works by lowering estrogen levels in the body.

What are the worst side effects of letrozole?

The worst side effects of letrozole can include severe bone pain, severe dizziness, and liver problems, but everyone's body can react differently so these might be different for you. If you are experiencing any side effects, be sure to speak with your doctor so they can help manage them.

Is letrozole a chemotherapy drug?

No, letrozole is not a chemotherapy drug. It is a type of hormone therapy used to block estrogen.

Does letrozole cause weight gain or loss?

Letrozole, a medication used in breast cancer treatment, may contribute to weight gain as a common side effect, especially in postmenopausal women. However, individual responses can vary, and it's essential to discuss any concerns about weight changes with healthcare providers for personalized guidance.

What is the most common side effect of letrozole?

The most common side effect of letrozole is experiencing hot flashes, which are sudden feelings of warmth and sweating. Many individuals undergoing letrozole treatment may encounter this side effect, but its intensity and frequency can vary from person to person.

Is weight gain common with letrozole?

Yes, weight gain is a common concern for some individuals taking letrozole, especially among postmenopausal women. It's important to communicate any changes in weight with healthcare providers to address concerns and explore personalized management strategies.

Does letrozole affect metabolism?

Letrozole can influence metabolism, and some individuals may experience changes in their metabolic rate while taking the medication. It's advisable to discuss any concerns or noticeable changes in metabolism with healthcare providers for personalized guidance.

What does letrozole do to a woman's body?

Letrozole works by blocking the production of estrogen in a woman's body, which helps in treating certain types of breast cancer by slowing down or stopping the growth of cancer cells.

How to avoid weight gain on letrozole

To avoid weight gain on letrozole, maintaining a healthy diet, staying active with regular exercise, and staying hydrated are important measures that may help control weight.

Does letrozole cause hair loss?

Hair loss is not a common side effect of letrozole, and most individuals do not experience significant hair loss while taking the medication.

What not to do while taking letrozole?

While taking letrozole, it's important not to skip doses, and it's advisable to avoid excessive alcohol consumption and smoking to optimize its effectiveness.

What are the signs that letrozole is working?

Signs that letrozole is working include a decrease in the size or spread of the cancer, improvement in symptoms, and positive results in medical tests as indicated by healthcare providers.

Is it better to take letrozole in the morning or at night?

The best time to take letrozole, whether in the morning or at night, should be discussed with a healthcare provider, as it may vary based on individual preferences and tolerance.

What happens after 5 years of taking letrozole?

After 5 years of taking letrozole, healthcare providers may reassess the treatment plan and consider further options based on the individual's health and the status of the cancer.

Does letrozole affect sleep?

Letrozole can impact sleep in some individuals, and if sleep disturbances occur, it's recommended to discuss this with healthcare providers for possible solutions.

What is the life expectancy of someone on letrozole?

The life expectancy of someone on letrozole depends on various factors, including the stage of cancer, overall health, and response to treatment, and should be discussed with healthcare providers.

Which has worse side effects, tamoxifen or letrozole?

The comparison of side effects between tamoxifen and letrozole varies for each individual, and the choice between them is determined by factors such as cancer type and patient preferences.

Is there a better drug than letrozole?

The determination of whether there is a better drug than letrozole depends on individual health conditions, the type of cancer being treated, and the response to the medication. This is a question you can ask your care team.

What is the success rate of letrozole?

The success rate of letrozole in breast cancer treatment varies, and it is essential to discuss individual prognosis and outcomes with healthcare providers.

Which brand of letrozole has the least side effects?

Different brands of letrozole may have similar side effects, and it's advisable to discuss preferences and concerns with healthcare providers to find the most suitable option.

Which is safer anastrozole or letrozole?

The safety comparison between anastrozole and letrozole should be discussed with healthcare providers based on individual health history and the specific condition being treated.

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