Macleaya cordata (M. cordata) is a herbal plant that has abundant amounts of sanguinarine, which has many biomedical properties. The effects of M. cordata dietary supplementation on the productive performance, some blood constituents, and growth- related genes’ expression were evaluated in turkey. M. cordata extract was dietary supplemented to turkey at levels of 25, 50, and 100 ppm and a control group. Growth performance measurements (FBW, ADG, and FCR) and production efficiency factor for turkey (BPEF) were similar (p > 0.05) in all supplemented groups. M. cordata has no adverse effects (p > 0.05) on the birds’ health regarding hematological (Hb, RBCs, WBCs, and PCV) and blood biochemical indices evaluating liver function, kidney function, and lipid profile. Moreover, the mRNA expression of growth-related genes, such as growth hormone receptor (GHR), insulin-like growth factor 1 (IGF-1), cyclooxygenase 3 (COX-3), adenine nucleotide translocase (ANT), and uncoupling protein 3 (UCP-3) were upregulated (p < 0.001) in M. cordata treatments with the highest value for SG50 compared with the control group. We concluded that exogenous M. cordata dietary supplementation upregulated the expression of growth-related genes in turkey at a level of 50 ppm without adverse effects on their health status regarding hematological and biochemical indices.