5-HT2B antagonist-2 (Compound 19c) is a 5HT2B receptor antagonist with an IC50 of 1.09 nM. It effectively downregulates the expression of fibrosis-related genes α-SMA, Timp1, Col1a1, and Col3a1, significantly reducing cellulose deposition. In a CCl4-induced liver fibrosis mouse model, it decreases the fibrotic area and inhibits the progression of fibrosis. This compound is useful for research into immune-inflammatory related diseases, particularly pulmonary fibrosis.