Skip to Content

Letrozole / ribociclib Side Effects

For the Consumer

Applies to letrozole / ribociclib: oral tablet

Along with its needed effects, letrozole/ribociclib may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking letrozole / ribociclib:

More common
  • Black, tarry stools
  • bloating or swelling of the face, arms, hands, lower legs, or feet
  • bloody or cloudy urine
  • chills
  • cough
  • decrease in height
  • difficult, burning, or painful urination
  • difficult or labored breathing
  • fever
  • frequent urge to urinate
  • lower back or side pain
  • pain in the back, ribs, arms, or legs
  • pale skin
  • sore throat
  • tightness in the chest
  • tingling of the hands or feet
  • ulcers, sores, or white spots in the mouth
  • unusual bleeding or bruising
  • unusual tiredness or weakness
  • unusual weight gain or loss

Some side effects of letrozole / ribociclib may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

More common

For Healthcare Professionals

Applies to letrozole / ribociclib: oral tablet


The most common adverse reactions and laboratory abnormalities (20% or more frequency) were decreased leukocyte count (93%), decreased neutrophil count (93%), neutropenia (75%), decreased hemoglobin count (57%), nausea (52%), decreased lymphocyte count (51%), increased ALT (46%), increased AST (44%), fatigue (37%), diarrhea (35%), alopecia (33%), leukopenia (33%), decreased platelet count (29%), vomiting (29%), constipation (25%), headache (22%), back pain (20%), and increased creatinine (20%).[Ref]


Very common (10% or more): Decreased leukocyte count (93%), decreased neutrophil count (93%), neutropenia (75%), decreased hemoglobin count (57%), decreased lymphocyte count (51%), leukopenia (33%), decreased platelet count (29%), anemia (18%), lymphopenia (11%)[Ref]


Very common (10% or more): Nausea (52%), diarrhea (35%), vomiting (29%), constipation (25%), stomatitis (12%), abdominal pain (11%)[Ref]


Very common (10% or more): Increased ALT (46%), increased AST (44%), abnormal liver function tests (18%)
Frequency not reported: Increased blood bilirubin[Ref]


Very common (10% or more): Fatigue (37%), pyrexia (13%), peripheral edema (12%)
Uncommon (0.1% to 1%): On-treatment death[Ref]


Very common (10% or more): Alopecia (33%), rash (17%), pruritus (14%)[Ref]

Nervous system

Very common (10% or more): Headache (22%)
Common (1% to 10%): Syncope[Ref]


Very common (10% or more): Back pain (20%)
Common (1% to 10%): Fractures
Uncommon (0.1% to 1%): Osteoporosis[Ref]


Very common (10% or more): Increased creatinine (20%)[Ref]


Very common (10% or more): Decreased appetite (19%), decreased phosphorus (13%), decreased potassium (11%)
Frequency not reported: Hypokalemia[Ref]


Very common (10% or more): Insomnia (12%)[Ref]


Very common (10% or more): Dyspnea (12%)[Ref]


Very common (10% or more): Urinary tract infection (11%)[Ref]


Common (1% to 10%): QT interval prolongation[Ref]


1. "Product Information. Kisqali Femara Co-Pack (letrozole-ribociclib)." Novartis Pharmaceuticals, East Hanover, NJ.

Some side effects of letrozole / ribociclib may not be reported. Always consult your doctor or healthcare specialist for medical advice. You may also report side effects to the FDA.

Disclaimer: Every effort has been made to ensure that the information provided is accurate, up-to-date and complete, but no guarantee is made to that effect. In addition, the drug information contained herein may be time sensitive and should not be utilized as a reference resource beyond the date hereof. This material does not endorse drugs, diagnose patients, or recommend therapy. This information is a reference resource designed as supplement to, and not a substitute for, the expertise, skill , knowledge, and judgement of healthcare practitioners in patient care. The absence of a warning for a given drug or combination thereof in no way should be construed to indicate safety, effectiveness, or appropriateness for any given patient. does not assume any responsibility for any aspect of healthcare administered with the aid of materials provided. The information contained herein is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. If you have questions about the substances you are taking, check with your doctor, nurse, or pharmacist.