Inclusion Criteria:

• Advanced cancer patients seen in outpatient clinics at MD Anderson Cancer Center, with presence of anorexia for at least one month, and accompanied by weight loss of > 5 % of pre-illness body weight in the last 6 months. Anorexia on the day of enrollment (day 0 +/-3) must be > 4/10 on ESAS.
• Patients > 18 years of age
• Karnofsky Performance score of > 40 at time of inclusion into study
• Ability to provide informed consent and comply with study procedures
• Ability and willingness to return to engage in telephone follow-up by research nurse on days 2 (+/- 3 days), 8 (+/- 3 days), 16 ( +/- 3 days), and 22 (+/- 3 days) and return to outpatient clinic for evaluation on days 15 (+/- 3 days), and 29 (+/- 3 days).
• Negative urine pregnancy test at time of inclusion into study for female patients of childbearing potential, within 24 hours of study enrollment.
• For patients receiving chemotherapy eligibility to be determined after discussion with primary oncologist
• Drowsiness of </= 4/10 on ESAS at baseline due to known potential sedating effects of Mirtazapine
• Patient can continue all medications including complementary therapies or antineoplastic therapy while on-study (with the permission of their Attending MD) if they have been on stable dose for at least 2 weeks.

Exclusion Criteria:

• Patients who have known dementia or delirium at time of enrollment as determined by a physician.
• Known hypersensitivity to any ingredient of Mirtazapine
• Inability to maintain oral intake over the course of the study, such as with mechanical obstruction of the alimentary tract or intractable vomiting
• Ongoing use of tube feeding or parenteral nutrition
• Use of any antidepressant medication for longer than one week in the past month prior to study enrollment.
• Current use of corticosteroids (with the exception of scheduled doses during time of chemotherapy), dronabinol, testosterone and progesterone derivatives such as megestrol acetate, or in the preceding 1 week prior to study enrollment.
• Pregnancy or lactation or unwillingness to use contraceptives
• A score of 11 or more, in each subscale of the Hospital Anxiety and Depression scale (HADS) indicating clinical depression or anxiety. Those with HADS scores of > 11 at baseline indicating moderate or severe depression will be excluded from the study and will be referred for appropriate follow up by counselor and psychiatry evaluation.
• Patients on chronic use of benzodiazepines are excluded