A pharmaceutical composition for the treatment of an estrogen-dependent disease or condition comprises: (1) at least one polysaccharide selected from the group consisting of an alginate and a fucoidan in a quantity effective to treat an estrogen-dependent disease or condition； and (2) a pharmaceutically acceptable carrier. The composition can include both an alginate and a fucoidan. The composition can include other ingredients such as at least one compound selected from the group consisting of diindolylmethane and indole-3-carbinol in a quantity sufficient to inhibit the activity of estrogen. Methods for use of the composition for the treatment of an estrogen-dependent disease or condition, especially endometriosis, are described.
