It may take time before your thyroid function becomes normal after you begin taking thyroid hormone replacement. You will need to have blood tests until your thyroid levels are normal. You should eat a high-fiber diet and drink plenty of fluids to reduce the risk of constipation. If you are overweight, you should cut down on your calories and exercise for at least 30 minutes a day. If you have high blood pressure, you should lower your sodium intake. If your cholesterol is high, you should eat a high-fiber and low-fat diet.