Yonsa (abiraterone acetate) is a medication used to treat metastatic castration-resistant prostate cancer (CRPC) - prostate cancer that has spread to other parts of the body and no longer responds to other treatments that lower testosterone.

Yonsa is a CYP17 inhibitor and a type of hormone therapy approved by the US Food and Drug Administration (FDA) for use in combination with oral methylprednisolone, which is a corticosteroid like prednisone, but slightly stronger.

Yonsa is used in combination with methylprednisolone because methylprednisolone helps to prevent some of the side effects caused by Yonsa.

CYP17 inhibitors, such as Yonsa, block androgen biosynthesis and glucocorticoid production. Decreased levels of the key glucocorticoid cortisol increase adrenocorticotropic hormone (ACTH) release, which can cause the adrenal glands to increase mineralocorticoid production. Mineralocorticoid excess can lead to hypertension (high blood pressure), hypokalemia (low potassium) and fluid retention.

Taking Yonsa in combination with the corticosteroid methylprednisolone can help prevent the hypertension, hypokalemia and fluid retention that can result from treatment with the drug.