Initial Investigation: Thyroid Function Test
For a patient presenting with depression, loss of appetite, social isolation, anxiety, and medication non-compliance, the most appropriate initial investigation is a thyroid function test (TFT) to exclude medical causes before attributing symptoms to primary psychiatric illness. 1
Rationale for Thyroid Screening First
Depression and anxiety guidelines consistently emphasize treating medical causes of depressive symptoms before diagnosing primary psychiatric disorders. 1 Thyroid dysfunction—both hypothyroidism and hyperthyroidism—can present with the exact constellation of symptoms described: depression, anxiety, appetite changes, social withdrawal, and even medication non-compliance due to cognitive impairment or apathy from undiagnosed thyroid disease. 1
The critical principle: Do not prematurely diagnose primary psychiatric illness without excluding thyroid dysfunction, which can fully explain these symptoms and is readily treatable. 1
Why Not the Other Options
Urine Drug Test (Option B)
While the American Psychiatric Association recommends assessing substance use history as part of the initial psychiatric evaluation 2, and perioperative guidelines recommend routine screening for cannabis consumption 2, a urine drug test does not address the underlying medical causes that must be excluded first. The patient's stated desire to use marijuana (not current use) reflects a maladaptive coping strategy, but testing for substances doesn't rule out treatable medical conditions causing the psychiatric symptoms. 1
Complete Blood Count (Option C)
A CBC would be appropriate as part of a comprehensive workup for fatigue after thyroid dysfunction is excluded, as anemia can contribute to fatigue and depressive symptoms. 1 However, it does not explain the full symptom constellation including anxiety, social isolation, and medication non-compliance as comprehensively as thyroid dysfunction would. 1
Pulmonary Function Test (Option D)
This has no role in the initial investigation of psychiatric symptoms unless there are specific respiratory complaints or concerns about cannabis-related pulmonary disease, which is not the presenting concern here. 2
Structured Approach After Thyroid Screening
Once thyroid dysfunction is excluded, proceed with comprehensive psychiatric assessment: 2, 3
- Screen for suicidal ideation immediately in all patients with depression and anxiety, as suicide risk is elevated. 3
- Use validated screening tools: PHQ-9 for depression (scores ≥10 indicate moderate depression) and GAD-7 for anxiety (scores ≥10 indicate moderate anxiety). 2, 1, 3
- Assess substance use history comprehensively, including the patient's use of tobacco, alcohol, marijuana, and any misuse of prescribed medications. 2
- Evaluate medication non-compliance: Explore specific reasons such as side effects, cost, denial of illness, or frustration with polypharmacy. 3
- Document functional impairment in work, social interactions, and activities of daily living. 3
Common Pitfalls to Avoid
- Never dismiss the patient's desire to use marijuana without proper assessment—this increases anxiety and reduces trust in healthcare providers. 3
- Do not initiate psychiatric treatment before excluding medical causes, particularly thyroid dysfunction, which is the most common medical mimic of psychiatric illness in this presentation. 1
- Avoid adding benzodiazepines if the patient has any substance use history, as this poses high relapse risk. 4
Cannabis Considerations
The literature on cannabis for anxiety and depression is mixed. While some observational studies suggest medicinal cannabis use may reduce anxiety and depressive symptoms 5, strong evidence points to depression leading to increased cannabis use frequency rather than cannabis effectively treating depression. 6 Cannabis use is linked to poorer clinical course in bipolar disorder and PTSD, though findings are less clear in depression and anxiety disorders. 7 There is insufficient evidence to support cannabis as an antidepressant at this stage. 6