In vivo models are research methods that involve studying living organisms to understand biological processes, diseases, and the effects of treatments. These models can include animals like mice, rats, or even larger mammals, and they help scientists observe how a drug or therapy works in a complex living system, which is often more relevant than laboratory tests. These models are essential for testing the safety and efficacy of new medications before they are used in humans. By using in vivo models, researchers can gather valuable data on how treatments interact with various body systems, paving the way for advancements in fields like pharmacology and medicine.