A method of treating a patient comprises orally administering a solid oral dosage form comprising a core comprising a non-ionic polymer matrix, a first amount of ondansetron dispersed within the matrix, and a salt dispersed within the matrix, wherein the first amount of ondansetron ranges from about 9 mg to about 28 mg; a first seal coat surrounding the core, wherein the first seal coat is comprised of a non-ionic polymer matrix; and an immediate release drug layer surrounding the first seal coat and comprising a non-ionic polymer and a second amount of ondansetron dispersed therein, wherein the second amount of ondansetron ranges from about 3 mg to about 8 mg, wherein release of ondansetron from the solid oral dosage form provides exposure to ondansetron for a minimum period of 16 hours so as to result in a reduction in frequency of vomiting, nausea, diarrhea, or a combination thereof.