Individuals undergoing chemotherapy with melphalan often experience nausea and vomiting. This study examines if lower doses of a medication called olanzapine can help reduce these side effects. Olanzapine has been effective in previous studies but can cause sleepiness. We will compare 2.5 mg and 5 mg doses of olanzapine, alongside three other standard medications, to find the dose that best reduces nausea and vomiting with minimal sleepiness.

This is a randomized, double-blinded trial. Randomized means participants are randomly chosen to receive either 2.5 mg or 5 mg doses, while double-blinded means neither the participants nor the researchers know who receives which dose. The study targets patients with multiple myeloma receiving high-dose melphalan before autologous stem cell transplantation.

• Study includes patients receiving high-dose melphalan.
• Cannot participate if allergic to olanzapine or taking certain medications.
• No cost to participants; study covers all related expenses.