• Mendelian randomization reveals causal links between burn injury and reduced levels of interleukin-9 and testosterone.
• No heterogeneity or horizontal pleiotropy was detected, confirming the robustness of the findings.
• Elevating interleukin-9 and testosterone levels may facilitate tissue repair and mitigate protein catabolism post-burn.
• The study integrates multi-omic data from large biobanks to overcome limitations of observational studies.