Provided herein are compositions, systems, and methods for treating a disease, such as kidney and/or cardiovascular disease, with an agent that reduces the production of trimethylamine (TMA) or trimethylamine-n-oxide (TMAO) in a subject. In certain embodiments, the agent is: i) 3,3-dimethyl-1-butanol (DMB) or a DMB derivative or related compound, ii) acetylsalicylic acid or derivative thereof (e.g., with an enteric coating for delivery to the colon and/or cecum); iii) a flavin monooxygenase 3 (FMO3) inhibitor; iv) a gut TMA lyase inhibitor; v) an antibiotic or antimicrobial; vi) a probiotic or prebiotic; vii) an antiplatelet agent; or viii) a TMA and/or TMAO sequestering agent.