Managing Anorexia During Chemoradiation With Olanzapine (MACRO)

Inclusion Criteria: * Age ≥ 18 years old * Have an Eastern Cooperative Oncology Group (ECOG) performance status of ≤ 2 * Diagnosed with biopsy-proven, squamous cell carcinoma of the head and neck, including squamous cell carcinoma of the neck with unknown primary site * Eligible for curative-intent chemoradiation therapy of the head and neck * Patients must be eligible for concurrent systemic therapy (preferably platinum based) as determined by the treating medical oncologist to undergo platinum-based chemotherapy * Ability to swallow and retain oral medication * Participants of child-bearing potential must agree to use adequate contraceptive methods (e.g., hormonal or barrier method of birth control; abstinence) prior to study entry. Should a woman become pregnant or suspect she is pregnant while she or her partner is participating in this study, she should inform her treating physician immediately * Participants must agree to avoid the following while taking Olanzapine while they are on study: * Taking the drug Symbyax (which already contains olanzapine) * Consuming alcohol * Operating hazardous machinery, including automobiles, until you are reasonably certain that the study drug therapy does not have any bad effects on your mental and physical health * Participant must understand the investigational nature of this study and sign an institutional review board approved written informed consent form prior to receiving any study related procedure Exclusion Criteria: * Eligible for palliative-intent radiation therapy only * Patients with a feeding tube * Regular systemic steroid use * Atypical antipsychotic use * Other dopamine receptor blockers routinely used as anti-emetics (eg. prochlorperazine/compazine and metoclopramide) are allowed to be prescribed as usual care on this study * Uncontrolled intercurrent illness including, but not limited to, ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, diabetes or psychiatric illness/social situations that would limit compliance with study requirements * Known hypersensitivity to olanzapine * Pregnant or nursing female participants * Known history of seizures * Unwilling or unable to follow protocol requirements * Any condition which in the investigator's opinion deems the participant an unsuitable candidate to receive study drug