Background: In September 2019, ranitidine, the largest share in the gastric acid secretion inhibitor market, was identified as a carcinogen, and sales were banned. The purpose of this study was to investigate how the gastric acid secretion inhibitor market changed after ranitidine withdrawal.Methods: From January 2010 to December 2021, the prescription dose and cost of gastric acid secretion inhibitors were calculated monthly. To investigate the effect of ranitidine withdrawal on the gastric acid secretion inhibitor market, we developed a time-series autoregressive model using data from January 2010 to October 2019. In addition, the P-value was calculated by interrupted time series analysis using the data dating between 2010 and 2021 (interrupted time: October 2019).Results: Since 2010, proton pump inhibitors have increased their market share in terms of prescription volume and drug costs. This trend accelerated since ranitidine was withdrawn from the market in September 2019. In 2021, it was estimated that ranitidine prescriptions would be transferred as follows: famotidine's increased prescription volume was estimated at 323 million (pharmaceutical cost, 53.2 billion won), proton pump inhibitors (PPIs) at 223 million (89.9 billion won), and lafutidine at 137 million (20.5 billion won).Conclusions: The market share expansion of PPIs accelerated due to the withdrawal of ranitidine. The ranitidine prescription was partially transferred to the same H <sub>2</sub> blockers, such as famotidine and lafutidine, and there was also a significant transfer to PPIs.