Solid phases of (-)-cis-FTC, which are designated herein as amorphous (-)-FTC and Forms II and III (-)-cis-FTC) are provided that can be distinguished from Form I (-)-cis-FTC by X-ray powder diffraction patterns, thermal properties, and methods of manufacture. A hydrated crystalline form of (.+-.)-cis-FTC (i.e. racemic cis-FTC), and a dehydrated form of the hydrate, are also provided, and can similarly be distinguished from other forms of FTC by X-ray powder diffraction patterns, thermal properties, and methods of manufacture. These FTC forms can be used in the manufacture of other forms of FTC, or in pharmaceutical compositions. Particularly preferred uses of these forms are in the treatment of HIV or hepatitis B.