The invention relates to a crystalline diethylamine tetrathiomolybdate salt (DEA-TTM). The invention also relates to methods for producing the crystalline DEA-TTM salt of the invention. The invention also relates to pharmaceutical compositions comprising the crystalline DEA-TTM salt of the invention. The invention also relates to the use of the crystalline DEA-TTM salt of the invention in the treatment of the human or animal body, in particular its use in treatment of a condition requiring reduced metabolism of an organ or the whole body of a patient, by administering to a patient in need thereof a therapeutically effective amount of the crystalline DEA-TTM salt.