Technologies for Removing Residual Solvent from Nalmefene Hydrochloride and Producing Crystalline Nalmefene Hydrochloride Monohydrate, Monosolvate, or Crystalline Nalmefene Hydrochloride Dihydrate: 10,927,121

Methods for removing residual solvent from Nalmefene Hydrochloride (HCl) and producing crystalline Nalmefene HCl monohydrate, monosolvate or crystalline Nalmefene HCl dihydrate are described. In embodiments, the methods include recrystallizing Nalmefene HCl from a solvate that includes Nalmefene HCl, water, and a first solvent, wherein the first solvent has a molar volume of at least 98 cm.sup.3. Crystalline Nalmefene HCl with a desirably low amount of residual solvent is also described.