Leucine in Midlife Depression

This study tests whether leucine — an amino acid found in protein-rich foods — can improve mood and motivation in middle-aged people with moderate to severe depression. Depression in midlife often involves a loss of pleasure and low energy, and leucine may help by supporting brain chemistry related to reward and motivation. **You may be eligible if...** - You have been diagnosed with major depression (confirmed by a structured interview) - Your depression is moderate to severe based on a standard questionnaire - You are a certain age range and BMI (details confirmed at screening) **You may NOT be eligible if...** - You have certain metabolic disorders that affect how your body processes amino acids - You are taking medications that could interact with leucine - You have other major psychiatric conditions Talk to your doctor to see if this trial is right for you.