You probably already know that taking tamoxifen (sold as Soltamox) can cause hot flashes or make you feel too warm. Some MyBCTeam members have commented that instead, they feel chilled all the time. One member asked, “Anyone who’s on tamoxifen and just feels cold?”

Another member who takes tamoxifen replied, “I get really cold and mentioned these symptoms to the oncologist, and they told me they were typical.” Despite chills and feeling cold being fairly common among people with breast cancer, there hasn’t been much research on this effect.

If you take tamoxifen and have noticed that you feel cold all the time, you’re not alone. Read on to learn more about how this medication can cause chills.

What Are Chills?

The term “chills” refers to feeling cold, sometimes accompanied by shivering. It’s usually a sign that your body is working to regulate your core temperature.

The symptoms of chills include:

• Shivering or shaking — Your muscles involuntarily contract and relax.
• Chattering teeth — Your jaw shivers, making your teeth bump together.
• Goose bumps — The tiny muscles in your hair follicles make your hair stand upright.

What Causes Chills?

The symptoms of chills represent your body’s attempt to stay at the right temperature. This process is called thermoregulation.

The most common causes of chills include:

• Bacterial Infections, such as pneumonia and urinary tract infections
• Viruses, such as influenza
• A hangover from excessive alcohol intake
• Low blood sugar
• Night sweats or hot flashes due to menopause or hormonal changes
• Panic attacks
• Some types of cancer, such as breast cancer and leukemia

When you’re too cold, your body sends signals to your muscles to contract and relax to generate more heat, causing the symptoms of chills.

Factors that can affect body heat include:

• Room temperature — Your body needs more energy to keep you warm when the air is cooler.
• Food — Eating gives you the energy to maintain your internal temperature.
• Exercise — You may feel warm during a workout but cooler as your sweat dries.
• Age — Your body temperature typically lowers as you get older.

Breast cancer survivors often feel uncomfortable — either too hot or too cold — at temperatures that others consider ideal.

Are Chills a Common Side Effect of Tamoxifen?

Tamoxifen is a hormone therapy used for hormone receptor-positive breast cancer treatment. Chills aren’t listed as one of tamoxifen’s side effects.

The most common side effects of tamoxifen include:

• Hot flashes (also known as hot flushes)
• Fatigue (extreme tiredness)
• Weight loss
• Vaginal discharge
• Hair thinning or hair loss
• Rash
• Edema (swelling in your hands, feet, or ankles)
• Depression
• Loss of libido

Less common but potentially serious side effects include:

• Muscle pain
• Joint pain
• Life-threatening blood clots in the lungs or lower legs
• Liver problems
• Anemia (low red blood cell count)
• Blurred vision
• Unusual vaginal bleeding

How Can Tamoxifen Cause Chills?

Despite chills not being listed as a common or uncommon side effect of tamoxifen, they are often mentioned by MyBCTeam members. “I will feel cold, like I just can’t get warm. Then I get really warm. I have been on tamoxifen for almost three years,” one member said.

If you take tamoxifen and experience chills, it could be due to changes in your hormones. Tamoxifen is a selective estrogen receptor modulator. It blocks estrogen, which can encourage cell growth in some cancers. As a result of estrogen being blocked, many people experience side effects similar to those of menopause, especially hot flashes and sweating.

Hot flashes are often followed by chills as your sweat dries and you lose heat through your skin. A MyBCTeam member described their experience with this: “I had cold flashes and hot flashes — I went from one extreme to the other.”

Could Breast Cancer Lead to Chills?

Breast cancer treatment — and the disease itself — may also cause chills. “I have a hard time feeling normal warm. I have a duvet and a thick fleece blanket on top and a hot water bottle in bed. Brrrr!” shared a MyBCTeam member.

Most medical research on temperature regulation in breast cancer survivors focuses on feeling too hot from menopauselike symptoms and medication side effects. Although there isn’t as much research on why survivors may feel cold, several factors could come into play.

Fatigue

Your body uses a lot of energy to keep you warm. If you are tired from breast cancer or treatment, it can affect your ability to maintain your internal temperature.

Fatigue caused by breast cancer or treatment can reduce the amount of energy available to your body to keep warm. Additionally, there’s evidence that breast cancer might disrupt the internal clock that regulates your body temperature based on the time of day.

Infection

When your body is fighting off an infection, you may experience chills. Breast cancer treatments, such as chemotherapy and targeted therapy, can make you more likely to get an infection. These treatments can decrease the number of immune cells responsible for fighting infections, called white blood cells, which can lead to thermal dysregulation (impaired ability to maintain a steady body temperature).

Loss of Appetite

If you aren’t eating enough because the side effects of your breast cancer treatment cause a loss of appetite, it can reduce how much energy is available in your body to keep you warm. Lack of appetite can also result in an increase in certain plasma cells and lead to thermal dysregulation over time.

When Should You Talk to Your Doctor About Chills?

It’s important to talk to your health care provider if you notice any new, lingering, or worsening symptoms, such as chills. Be sure to seek immediate medical advice if you experience chills along with any of the following symptoms:

• Fever
• Chest pain
• Unexplained pain in any part of the body
• Unusual or extreme fatigue
• Abdominal pain
• Shortness of breath

Never hesitate to contact your doctor regarding a new or worsening symptom, such as chills. They can help you discover if your symptoms are caused by a medication you’re taking or another health condition and help you find ways to manage them.

Talk With Others Who Understand

MyBCTeam is the social network for people with breast cancer and their loved ones. On MyBCTeam, 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 chills while taking tamoxifen or other breast cancer treatments? Do you have advice about managing this side effect? Share your experiences in the comments below, or start a conversation by posting on your Activities page.