ICD-10 Coding for Mirtazapine Used as Appetite Stimulant
For a patient taking Remeron (mirtazapine) specifically for appetite stimulation, use R63.0 (Anorexia) as the primary diagnosis code, which accurately captures loss of appetite as the clinical indication. 1
Primary Diagnosis Options
R63.0 (Anorexia) is the most appropriate code when the primary indication is poor appetite or loss of appetite without weight loss being the predominant feature. 1
R63.4 (Abnormal weight loss) should be used if documented weight loss is the primary clinical concern, particularly if the patient has lost ≥7% of body weight. 2
R63.6 (Underweight) can be considered if the patient's BMI is documented as below normal range and this is the focus of treatment. 1
Context-Specific Coding Considerations
If Depression is Present
- F32.9 (Major depressive disorder, single episode, unspecified) or F33.9 (Major depressive disorder, recurrent, unspecified) should be the primary diagnosis, as mirtazapine addresses both depression and appetite simultaneously in elderly patients. 1
- This is particularly relevant since mirtazapine 7.5-30 mg at bedtime is specifically recommended for elderly patients with appetite loss and concurrent depression. 1
If Dementia is Present
- Avoid using mirtazapine as an appetite stimulant in patients with dementia who do not have concurrent depression, as evidence shows no consistent benefit and potentially harmful side effects. 1
- If prescribed despite this recommendation, code the underlying dementia (F01-F03 series) as primary diagnosis. 1
If Cancer-Related
- R63.0 (Anorexia) remains appropriate, but consider adding the underlying malignancy code as a secondary diagnosis. 1
- Document that this is cancer-related cachexia if applicable. 1
Common Pitfalls to Avoid
Do not use F50.0x (Anorexia nervosa) codes unless the patient has a diagnosed eating disorder, as this represents a psychiatric condition distinct from simple loss of appetite. 3
Do not use Z79.899 (Other long-term drug therapy) as the primary diagnosis—this is a supplementary code only. 1
Avoid E46 (Unspecified protein-calorie malnutrition) unless formal nutritional assessment documents malnutrition, as this requires specific diagnostic criteria beyond poor appetite alone. 1
Documentation Requirements for Billing
Document the specific indication clearly in the medical record: "Mirtazapine prescribed for appetite stimulation" with baseline weight and appetite assessment. 2
Note any concurrent conditions (depression, dementia, cancer) that influence the appropriateness of this medication choice. 1
Record the expected therapeutic outcome: mirtazapine typically produces appetite increase in 17% of patients and weight gain of ≥7% in 7.5% of patients compared to placebo. 2
Plan for reassessment at 4-8 weeks, as a full therapeutic trial requires this duration to assess efficacy. 1