How long do letrozole side effects last?

Medically reviewed by Carmen Pope, BPharm. Last updated on Sep 17, 2024.

Official Answer by Drugs.com

Most side effects of letrozole are mild and temporary, lasting only a few days or weeks until your body gets used to taking the medication. Some other side effects of letrozole take a few months to develop and tend to persist long term until you stop taking letrozole. The half-life of letrozole is 2 days, so once you stop taking letrozole, you might continue to experience side effects for about a week to 10 days after your last dose.

Side effects that are more likely to be temporary and resolve within a few days or weeks include:

difficulty sleeping
dizziness
excessive sweating
fatigue (lack of energy)
feeling drowsy, weak, or tired
headache
hot flashes
nausea
vaginal bleeding or spotting.

Allergic reactions to letrozole are rare and symptoms include rash, itching, or swelling of the face, tongue, throat, or neck, severe dizziness, or trouble breathing and are most likely to happen within a few hours of starting letrozole.

Side effects that are more likely to take a few months to develop and persist long term include:

blood changes, such as decreases in white blood cell counts or platelets
edema (swelling that usually affects your hands, feet, legs, or arms)
hair loss
high cholesterol
low bone density (low levels of calcium and minerals in your bones)
low mood
weight gain
joint pain
muscle pain or bone pain.

Side effects that may take a while to resolve even after stopping letrozole include:

low bone density that may increase the risk of bone fractures and/or osteoporosis
weight gain.

Letrozole is not known to cause withdrawal symptoms on stopping it.

Talk to your doctor or pharmacist if your side effects last longer than expected, bother you, or become severe. Most people are given letrozole for 5 years, but some will take it for up to 10 years.

Letrozole is an oral prescription medication used for the treatment of breast cancer in postmenopausal women.

Is letrozole a form of chemotherapy?

Letrozole is not chemotherapy, it is a type of hormone therapy that is used to treat people with breast cancer that is hormone receptor-positive. If your cancer is hormone receptor-negative, then letrozole will not be of any benefit. Traditional chemotherapy agents stop cancer cells from growing, dividing, and making more cells. Letrozole works by blocking the action of the enzyme aromatase, which prevents the body from converting androgens into estrogens. Estrogen is a hormone that causes estrogen receptor-positive (ER+) breast cancer to grow. Letrozole belongs to the class of medicines known as aromatase inhibitors. Continue reading

Does letrozole affect blood sugar levels?

Although diabetes and blood sugar increases are not listed as a side effect of letrozole treatment, treatment with letrozole is associated with a significantly increased risk for high blood sugar levels and diabetes. An Israeli study that investigated 2,246 breast cancer survivors found that women treated with letrozole were 4.3 times more likely to develop diabetes than women not taking letrozole, although the number of women prescribed letrozole was small. Overall, women prescribed any sort of hormone treatment (either tamoxifen or an aromatase inhibitor such as letrozole) had a 2.5 times higher risk of diabetes. Continue reading

How long do letrozole side effects last?

Related questions

Read next

Is letrozole a form of chemotherapy?

Does letrozole affect blood sugar levels?

See also:

Aimovig

Botox

Enhertu

Nurtec ODT

Vyepti

Depakote

Topamax

Emgality

Inderal

Ajovy

Related medical questions

Drug information

Related support groups