The present invention relates to preventing and treating leukemia and other cancers of the blood and bone, as well as disorders of the blood, by inhibiting gut-derived serotonin. The inhibition of the gut-derived serotonin is accomplished by inhibiting Tph1, an enzyme responsible for the production of gut-derived serotonin. The present invention also relates to preventing and treating leukemia and other cancers of the blood and bone, as well as disorders of the blood, by increasing the number, growth and proliferation of osteoblasts.
