Thyroid desiccated and multivitamin with iron and fluoride should not be taken orally at the same time. Products that contain iron may interfere with the absorption of thyroid desiccated and reduce its effectiveness. You should separate the dosing of these medications by at least 2 to 4 hours if possible. Contact your doctor if your condition changes or you experience symptoms of hypothyroidism such as dry skin, weight gain, cold intolerance, weakness, muscle cramps or stiffness, slow pulse, or constipation. It is important to tell your doctor about all other medications you use, including vitamins and herbs. Do not stop using any medications without first talking to your doctor.