More than just an underactive thyroid may cause significant weight gain. Once your hypothyroidism is corrected -- it can take several weeks for L-thyroxine to work -- your metabolism will be back to normal. Recent Examples on the Web. Your thyroid produces hormones like thyroxine and triiodothyronine, which influence many of your body’s systems, according to the Mayo Clinic. What is a Thyroxine (T4) Test? A thyroxine test helps diagnose disorders of the thyroid. The thyroid is a small, butterfly-shaped gland located near the throat. Your thyroid makes hormones that regulate the way your body uses energy. It also plays an important role in regulating your weight, body Recent Examples on the Web. Your thyroid produces hormones like thyroxine and triiodothyronine, which influence many of your body’s systems, according to the Mayo Clinic. The function of the thyroid gland is to take iodine, found in many foods, and convert it into thyroid hormones: thyroxine (T4) and triiodothyronine (T3). Response to thyroxine (levothyroxine sodium) is best monitored biochemically. Thyroid function should be assessed every 6-8 weeks until the patient is euthyroid and then rechecked annunally, aiming to maintain T4 and TSH within the normal range (1). In most cases, the exact cause of thyroid cancer is unknown. However, there are certain things that can increase your chances of developing the condition, including having another thyroid condition and being exposed to radiation. Learn about Levothroid (Levothyroxine Sodium) may treat, uses, dosage, side effects, drug interactions, warnings, patient labeling, reviews, and related medications. None needed; however, certain medications, multivitamins and supplements can interfere with the free T4 test, so tell your healthcare provider about any prescribed or over-the-counter drugs and/or supplements that you are taking. The thyroid gland is located in the neck and produces thyroid hormones. These are called thyroxine (T4) and tri-iodothyronine (T3) and are carried round the body in the bloodstream.