PGP and cancer: Mechanistically, released H2 assists chemotherapeutic drug to efficiently inhibit cancer metastasis by immunoactivating intratumoral M1‐phenotype macrophages and consequently downregulating the expression of metastasis‐related matrix metalloproteinase‐2 (MMP‐2) and can also downregulate the expressions of both P‐glycoprotein (P‐gp) protein and adenosine triphosphate (ATP) in MDR cancer cells to sensitize chemotherapeutic drug for enhanced damage to mitochondria and DNA.