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How long does it take for Yonsa to work?

Medically reviewed by Philip Thornton, DipPharm. Last updated on Dec 26, 2022.

Official answer


Yonsa (abiraterone acetate) is a hormone therapy used to treat prostate cancer that has spread to other parts of the body and no longer responds to other medical and surgical treatments that lower testosterone - metastatic castration-resistant prostate cancer (CRPC). Yonsa is taken in combination with methylprednisolone.

Yonsa is a CYP17 inhibitor that works by blocking the production of androgens used to make testosterone. Androgens are a group of hormones that includes testosterone, which play a key role in the development and function of the prostate gland. Androgens are also involved in the initiation and progression of prostate cancer.

Yonsa contains the same active ingredient as Zytiga, but it provides the drug in a smaller, finer particle size (micronized) than Zytiga.

So, how quickly does Yonsa work?

Yonsa starts working quickly to lower testosterone levels in men with advanced prostate cancer.

The results of the STAAR study showed that 25% of the men with metastatic CRPC treated with Yonsa achieved averaged absolute testosterone levels at or below 0.1 ng/dl by days 9 and 10 of treatment.

In addition, more than 90 percent of the 24 men who received Yonsa during the study achieved absolute testosterone levels of ≤1 ng/dl during the 84 days that patients were monitored.

A decrease from baseline of ≥50 percent in prostate-specific antigen (PSA-50 response) levels was also observed in more than 65 percent of patients in the study on days 28, 56 and 84.

The STAAR study found Yonsa to be therapeutically equivalent to Zytiga based on serum testosterone levels.


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