This invention relates to relates to methods for producing gossypol acetic acid co-crystals and (-)-gossypol acetic acid co-crystals. The invention also relates to pharmaceutical compositions comprising gossypol acetic acid co-crystals and (-)-gossypol acetic acid co-crystals and the use of gossypol acetic acid co-crystals and (-)-gossypol acetic acid co-crystals for inducing apoptosis in cells and for sensitizing cells to the induction of apoptotic cell death.