Olanzapine 2.5 vs 5 mg in Quadruplet Nausea/Vomiting Prophylaxis Before High-Dose Melphalan

Patients who receive a chemotherapy called melphalan are at high risk of having nausea and vomiting. A medication called olanzapine has been shown to decrease nausea and vomiting after chemotherapy. A previous research study found the 10 mg dose of olanzapine (combined with 3 standard medications used routinely to prevent nausea/vomiting) to be effective for patients who received melphalan chemotherapy, but several other studies have shown many patients have a side effect of sleepiness (e.g., sedation) with that dose of the medication. Our study will compare two lower doses of olanzapine (5 mg and 2.5 mg) in combination with the 3 standard medications used to prevent nausea/vomiting in the patients who receive melphalan chemotherapy to determine which dose is effective in preventing nausea and vomiting with the lowest amount of sleepiness side effect.