The consumption of medicinal herbs has increased in recent years. There is little evidence with regards to their benefits and a small number of scientific papers about adverse effects, especially related to interactions with other drugs. Ribociclib is approved as starting endocrine-based therapy in combination with an aromatase inhibitor for women diagnosed with advanced breast cancer with HR-positive, HER2-negative. A case of a 55-year-old woman is presented with recent diagnosis of luminal A

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... e novo metastatic breast cancer. The patient starts treatment with Ribociclib and letrozole. After 2 months, a partial response is achieved. However, the patient presents grade 4 hepatotoxicity with elevated bilirubin and transaminases. She is admitted to hospital for symptomatic treatment and ruling out other causes of liver failure. She had started to take Echinacea two months ago. After stopping the medicinal herb and Ribociclib, liver function improves only partially. This limits the choice of a second line for the treatment of metastatic breast cancer. Imaging tests show disease progression after 7 months and finally the patient died. Both Echinacea and Ribociclib present hepatic metabolism through cytochrome p450, which means that there could be a potential interaction between them. This is the first reported case of a potential interaction between Ribociclib and Echinaea. We highly recommend avoiding the concomitant use of both medications.