[6] The most common side effects include infections, low levels of white blood cells, headache, cough, nausea (feeling sick), vomiting, diarrhea, constipation, tiredness, hair loss and rash.

[4][7] In the European Union, it is indicated for the treatment of women with hormone receptor (HR)‑positive, human epidermal growth factor receptor 2 (HER2)‑negative locally advanced or metastatic breast cancer in combination with an aromatase inhibitor or fulvestrant as initial endocrine-based therapy, or in women who have received prior endocrine therapy.

[5] In September 2024, the US Food and Drug Administration (FDA) expanded the indication for ribociclib, in combination with an aromatase inhibitor, for the adjuvant treatment of adults with hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative stage II and III early breast cancer at high risk of recurrence.

[5][13][14] The most common side effects in studies were decreased blood cell counts, mainly neutropenia (in 75% of patients, as compared to 5% under placebo), but also anemia (18% vs. 5%).

[4][9] The most common side effects include infections, low levels of white blood cells, headache, cough, nausea (feeling sick), vomiting, diarrhoea, constipation, tiredness, hair loss and rash.

Many cancer cells have shown abnormalities that increase the activity of CDK, leading to the inactivation of certain tumor suppressor genes.

[20] The European Society of Medical Oncology (ESMO) assigned the highest score on the 'Magnitude of Clinical Benefit Scale' for ribociclib.

[21] In the clinical trial relevant for the drug's approval, ribociclib significantly improved progression-free survival, that is, the time span the cancer did not get worse.

[9] In October 2024, the Committee for Medicinal Products for Human Use of the European Medicines Agency recommended a change to the terms of the marketing authorization for ribociclib to add the adjuvant treatment of people with hormone receptor-positive/human epidermal growth factor receptor 2-negative early breast cancer, at high risk of disease recurrence.