Ribociclib side effects: the complete list and timeline

Ribociclib, sold as Kisqali, is a CDK4/6 inhibitor tablet taken with hormone therapy for hormone receptor positive, HER2-negative breast cancer. Most people have some side effects, but many are mild, follow a predictable pattern and can be managed without stopping treatment. The most common is a fall in white blood cells, which usually causes no symptoms and is found on routine blood tests. Other common effects include tiredness, nausea, diarrhoea or constipation, headache, back pain, hair thinning, a rash or itchy skin, mouth soreness and a reduced appetite. Some important side effects are less common but need regular checks: rises in liver tests, and lengthening of the QT interval, a part of the heart rhythm seen on an ECG. Rarely, ribociclib can cause inflammation of the lungs or a severe skin reaction. Timing follows a rough pattern. Low white cell counts and nausea tend to appear in the first cycle or two, QT changes usually show in the first few weeks, and liver test rises mostly appear within the first months. Tiredness and hair thinning can build more slowly. In early breast cancer, a lower dose is used, and side effects are generally milder. Joint aches and hot flushes are often caused by the hormone tablet taken alongside, not by ribociclib itself. Your team will manage side effects with pauses, dose reductions and supportive medicines.

Most side effects are manageable

Many people continue treatment with a pause or lower dose when needed.

Some need tests to find

Low counts, liver changes and QT changes often cause no symptoms at first.

Report symptoms early

Mentioning problems early usually makes them easier to treat.

A long list can look frightening. It helps to know what it does and does not mean.

Nobody gets everything

Lists include every effect seen in trials. Most people have only a few, and many are mild.

Some effects come from the hormone treatment

Hot flushes, joint pain and vaginal dryness are often due to the aromatase inhibitor or ovarian suppression taken alongside.

Some people do stop

A small number stop ribociclib because of side effects despite dose changes. Other options then remain.

What this page cannot tell you

It cannot predict which side effects you will have or how strongly. Your team will review this with you at each visit.

Ribociclib is used at a lower dose in early breast cancer than in advanced breast cancer, and this affects the side effect picture.

In early breast cancer

Low white cell counts are still common, but tend to be less severe. Fewer people need dose reductions for them.

In advanced breast cancer

The higher starting dose means more people need a delay or dose change in the early cycles.

Liver and heart checks apply to both

Whatever the dose, blood tests and ECGs remain part of treatment, because these effects can still happen.