What is the most appropriate initial investigation for a patient presenting with depression, loss of appetite, social isolation, and substance use (specifically marijuana) to relieve stress, who also exhibits anxiety and non-adherence to depression medication?

Initial Investigation: Urine Drug Test

For a patient presenting with depression, social isolation, marijuana use for stress relief, and medication non-compliance, the most appropriate initial investigation is a urine drug test (Option B). 1

Rationale for Urine Drug Testing

Objective confirmation of substance use is essential before proceeding with any treatment plan. 1 A urine drug test serves multiple critical functions in this clinical scenario:

• Establishes baseline substance use patterns and confirms the patient's self-reported marijuana use, which is crucial given the medication non-compliance 1, 2
• Identifies other undisclosed substances that may be contributing to the psychiatric presentation 1, 2
• Provides objective data to guide treatment decisions and monitor progress over time 2

Why Cannabis Assessment Takes Priority

Cannabis withdrawal syndrome can significantly exacerbate underlying psychiatric disorders, including depression 3, 1. The syndrome occurs with abrupt cessation of prolonged or heavy cannabis use and manifests with:

• Irritability, anxiety, and altered mood 3, 1
• Sleep disturbances and decreased appetite 3, 1
• Physical discomfort including abdominal pain, tremors, and headaches 3

Users consuming more than 1.5 g/day of inhaled cannabis are at particularly high risk for withdrawal symptoms 3, 1, and these symptoms can complicate the clinical picture of depression.

Impact on Depression Treatment

The relationship between cannabis use and depression creates significant treatment challenges:

• Non-medical marijuana use is associated with higher suicidal ideation, worse mental health functioning, and fewer psychiatry visits 4
• Patients using marijuana non-medically show less improvement in depression symptoms and suicidal ideation over time compared to non-users 4
• Cannabis use may create barriers to care and reduce engagement with psychiatric services 4

Why Other Options Are Less Appropriate

Complete blood count (CBC) would be part of a comprehensive workup but is not the most appropriate initial investigation given the prominent substance use component 1. While CBC can identify underlying medical conditions, it does not address the immediate need to objectively document substance use patterns 1.

Pulmonary function tests would only be indicated if there were specific respiratory complaints related to smoking, not as an initial investigation for psychiatric symptoms 1.

Thyroid function tests, while important in evaluating depression, should come after establishing the substance use pattern, as cannabis withdrawal and ongoing use can significantly confound the psychiatric presentation 1.

Clinical Approach Following Urine Drug Testing

After obtaining urine drug test results 1, 2:

• Assess for cannabis withdrawal syndrome if the patient has recently reduced or stopped use 3, 1
• Screen for cannabis use disorder using validated assessment tools 1
• Evaluate for comorbid psychiatric conditions that may be masked or exacerbated by substance use 3, 1
• Consider that anxiety and depression are very common associated conditions with cannabis use 3

Important Clinical Pitfalls

Starting antidepressants without proper assessment of withdrawal and substance use patterns would be premature 1. This approach risks:

• Masking underlying substance-related symptoms 1
• Complicating the diagnostic picture 1
• Missing opportunities to address the primary driver of symptoms 4

The American Psychiatric Association recommends comprehensive assessment of substance use history, including patterns of use and potential misuse, as crucial for patients with altered mental status and substance use 3, 1.