Reaction products and methods for making and using such reaction products are provided. For example, a reaction product comprising an adduct formed from urea, formaldehyde, and a urease inhibitor is described, which can be provided in various forms. For example, such a reaction product can be in the form of a solid or solution. Such a reaction product can also be combined with one or more additional components, including but not limited to, additional urease inhibitor and/or a nitrogen-based fertilizer composition.