The present invention provides methods and compositions for treating thyroid-related medical conditions. Many thyroid-related medical conditions exist that go undiagnosed and untreated. These conditions may be prevented and treated with reduced folates and vitamin B12. Administration of reduced folates and vitamin B12 will prevent or treat cerebrospinal folate deficiency, which is linked to thyroid-related medical conditions. Administration of reduced folates and vitamin B12 will also prevent or treat conditions associated with masked megaloblastic anemia and hypothyroidism, and other conditions brought upon through improper thyroid function. Additionally, it is commonplace to treat many thyroid conditions with anti-thyroid drugs or thyroid stimulating drugs. This practice alone is also responsible for causing, or not beneficially addressing, adverse conditions that can be prevented or treated through the methods and compositions discussed herein.