Struggling with depression, mood swings, and brain fog in your 40s? It might not just be perimenopause. Thyroid dysfunction is a hidden cause of treatment-resistant depression in women over 40. Learn how to tell the difference between thyroid-related depression and perimenopause, the complete thyroid blood test checklist every woman needs, and research-backed natural solutions including selenium, omega-3s, and ashwagandha that actually help.