**Question:** A 20 year old man has presented with increased alcohol consumption and sexual indulgence, irritability, lack of sleep, and not feeling fatigued even on prolonged periods of activity. All these changes have been present for 3 weeks. The most likely diagnosis is -

A. Depression
B. Anxiety
C. Substance Use Disorder
D. Sleep Apnea

**Correct Answer:** **C. Substance Use Disorder**

**Core Concept:**
Substance Use Disorder (SUD) is a group of disorders characterized by an impaired control over substance use, persistent use leading to harmful consequences, and social and occupational dysfunction. It encompasses a spectrum of disorders, including alcohol use disorder (AUD), drug use disorder (DUD), and other specified substance use disorders (OSUD).

**Why the Correct Answer is Right:**
The patient's symptoms align with the diagnostic criteria for Substance Use Disorder, specifically alcohol use disorder (AUD). Over the past three weeks, the patient exhibits increased alcohol consumption, sexual indulgence, irritability, lack of sleep, and not feeling fatigued even after prolonged periods of activity. These symptoms persist despite the negative consequences and social and occupational dysfunction.

**Why Each Wrong Option is Incorrect:**

A. Depression: While depression may coexist with Substance Use Disorder, the patient's specific symptoms and lack of fatigue do not align with the core features of depression (fatigue, insomnia, and low mood).

B. Anxiety: Similar to depression, anxiety might coexist with Substance Use Disorder, but the patient's symptoms (lack of fatigue, increased alcohol consumption, sexual indulgence) do not align with the core features of anxiety disorders.

D. Sleep Apnea: The patient's symptoms (increased alcohol consumption, sexual indulgence, irritability) are not consistent with the core features of sleep apnea (snoring, excessive daytime sleepiness, and breathing pauses during sleep).

**Clinical Pearl:**
Substance Use Disorder is a complex condition influenced by genetic, environmental, and psychological factors. Early identification and intervention are crucial to prevent chronicity and associated complications. Treatment options include psychosocial interventions, pharmacotherapy, and in severe cases, detoxification procedures.