Thyroxine and triiodothyronine are the names of the main hormones your thyroid gland makes. They go to every cell in your body to control the rate of metabolism, so that the cells burn energy faster or slower. The thyroid uses iodine to make the hormones. The most common form is thyroxine. It has four iodine atoms and is abbreviated as T4. Triiodothyronine has three iodine atoms and is called T3.
When you need extra hormone, your prescription will probably be for one of the following: Levothroid®, Levoxyl®, Synthroid®, or Unithroid® (all brand names). The generic name for the thyroid pill is thyroxine. These are all synthetic forms of T4 and work in the body the same way your own hormone does.
Other thyroid pills are Cytomel®, which is T3, Thyrolar®, which is a synthetic mixture of T4 and T3, and dessicated thyroid (Armour®), which is a T4/T3 mixture made from powdered animal (pig) thyroid glands.
Take your pill at the same time every day, either in the morning on an empty stomach or at bedtime (it shouldn't keep you awake). Take calcium, iron, or other medicines at least 4 hours apart from your thyroid pill. In order to keep your thyroid hormone dose absolutely level, most doctors prescribe name brands rather than generics and don't switch brands. Check with your doctor if your insurance company recommends a change in brands, if your pharmacy makes a substitution, or your pills are a different color than usual when you get your prescription refilled.
The chief reason is that your own gland makes too little hormone, and you may have felt dragged-out, chilly, or depressed because your body function (metabolism) was subnormal. Common causes of failing thyroid production:
Extra thyroid hormone is also used to help control some other thyroid problems, including nodules in the gland, goiter (or overall enlargement of the gland), and preventing the recurrence of a cancer that has been treated and removed.
You feel well because your thyroid hormone is at the right level for you. But you mustn't stop taking the extra hormone as long as your gland won't make enough on its own. Most thyroid problems are lifelong, and supplementary hormone needs to be taken lifelong too.
You may be able to stop after recovering from the inflammation of postpartum or subacute thyroiditis, but not until your doctor assures you the condition has resolved.
Whatever the reason that you need extra thyroid hormone, the situation can change with time, and your dose may need to be adjusted or you may need other treatment. So keep in touch.