When you are hypothyroid, your thyroid gland is unable to produce enough — or even any — thyroid hormone. You need thyroid hormone to survive. So, when your gland has slowed down, been destroyed by radioactive iodine (RAI) treatment, or surgically removed, you need to get the missing hormone from prescription medication.
The treatment of hypothyroidism with medication is called thyroid hormone replacement. Thyroid hormone replacement drugs fall into several categories:
- Synthetic versions of the thyroid hormone thyroxine (T4), known generically as levothyroxine. The brands such as Synthroid, Levoxyl, and Tirosint.
- A synthetic version of the thyroid hormone triiodothyronine (T3), known generically as liothyronine. The only brand name in the United States is Cytomel. There are also specially prepared, time-released versions of liothyronine available by prescription from compounding pharmacies.
- Natural desiccated thyroid — abbreviated as NDT — which is a naturally-derived medication that includes both T4 and T3. NDT is made from the desiccated (dried) thyroid glands of pigs. NDT is available as a generic drug, known as Thyroid NP. Brand names include Nature-throid, WP Thyroid, and Armour Thyroid.
Levothyroxine / Synthetic T4 / Synthroid / Levoxyl / Tirosint
The most frequently prescribed drug used for thyroid hormone replacement is levothyroxine. Levothyroxine is sometimes abbreviated as l-thyroxine or LT4. Levothyroxine is a synthetic version of the T4 thyroid hormone. In your body, T4 is converted into T3, which is the active hormone that facilitates the delivery of oxygen and energy to your cells. Conventional treatment with levothyroxine assumes that this T4 to T3 conversion will happen seamlessly and effectively.
Generic levothyroxine tablets are made by several different generic manufacturers. Generic levothyroxine is considered expensive, and the retail price for a standard monthly dosage ranges from $15 to $30 a month. There are also several brand names of levothyroxine tablets available in the United States, including Synthroid and Levoxyl. Retail prices for the brand names are typically costlier than generics and run from $30 to $60 per month.
Another brand of levothyroxine is the specialty drug Tirosint. Tirosint was formulated for people with digestive problems, absorption issues, or allergies. Tirosint comes in as a liquid-filled capsule and is hypoallergenic. Tirosint tends to be costlier than brand-name levothyroxine tablets, and the typical retail price can be $120 or more per month.
Generic and brand-name levothyroxine drugs are considered bioequivalent, meaning that they are considered equals that can be substituted for each other. A caution, however: Bioequivalence does not mean that levothyroxine drugs are equally “bioavailable.” You may absorb one levothyroxine drug at a different rate than another, given their different fillers. For example, most people absorb Tirosint better and more quickly than levothyroxine tablets.
Also, it’s important to mention that Synthroid, unlike the other levothyroxine drugs, contains both acacia (a type of tree bark) and lactose. Acacia can trigger allergic reactions in people who have seasonal allergies/hay fever. And a substantial percentage of people have lactose intolerance. If you have these sensitivities, you may experience impaired absorption of Synthroid, and do better on another brand.
Finally, bioequivalence does not mean that the potency of the different levothyroxine drugs is the same. Levothyroxine is required by law to fall within 10 percent of its stated potency. That means if you have a 100 mcg tablet of levothyroxine, it legally can have a potency from 95 mcg up to 105 mcg. Each generic or brand of levothyroxine has its own consistent and stable potency.
The risk is that if you are taking one brand and substitute another, the change in potency could affect your treatment. This is of even greater concern when you are taking a generic because pharmacies typically refill with whichever generic they have available, made by a number of different companies.
To minimize the risk of potency changes, doctors recommend that if you have had thyroid cancer, or require close control of your thyroid treatment, that you are prescribed a brand name levothyroxine with no substitutions. (Note: If you can personally work with a pharmacist who will ensure you get the same generic manufacturer’s levothyroxine with each refill, this achieves the same effect.)
Liothyronine / Synthetic T3 / Cytomel
Your thyroid gland makes mainly T4 and some T3. As indicated, the T4 needs to be converted into T3 in order to be used by your cells.
The synthetic form of the T3 hormone is liothyronine, which is available as a generic tablet, and as the brand name Cytomel. Because T3 is shorter-acting and can be somewhat stimulating, some doctors and patients prefer a time-released, longer-acting form of T3 that can be specially compounded by prescription.
Rarely, thyroid patients may be treated with T3-only thyroid hormone replacement. More common is the use of a T3 drug along with levothyroxine, called T4/T3 combination treatment.
Natural desiccated thyroid / Nature-throid / Armour Thyroid
NDT, derived from the dried thyroid gland of pigs, contains natural forms of both the T4 and T3 hormones. NDT has been on the market since the early 1900s when it became the first commercial thyroid hormone replacement medication. A popular brand for many years was Armour Thyroid. Today, a generic NDT is available, along with Armour Thyroid, and the hypoallergic NDT drugs Nature-throid and WP Thyroid.
When levothyroxine was introduced in the 1950s, NDT lost much of its market share, as physicians were told that NDT was less reliable and less modern than levothyroxine. More recently, NDT has enjoyed a resurgence in market share, as research has shown that it is a safe, effective, and reliable alternative to levothyroxine, and is preferred by some patients.
Do you need T3?
Levothyroxine is considered the recommended and preferred thyroid hormone replacement drug for conventional and mainstream physicians, including most endocrinologists. The 2014 “Guidelines for the Treatment of Hypothyroidism” — published by the American Thyroid Association’s Task Force on Thyroid Hormone Replacement — recommend levothyroxine, and state that there is no recommended role for T4/T3 combination treatment or the use of NDT.
This is controversial, however, as a substantial percentage of patients and some practitioners have found that T4/T3 combination treatment or NDT appear to better relieve symptoms. There is research that supports the use of combination treatment and NDT in some patients:
A major study published in the New England Journal of Medicine reported that patients preferred — and benefitted from — T4/T3 combination treatment.
A study out of Denmark, published in the prestigious European Journal of Endocrinology, reported that T4/T3 combination therapy was superior to T4/levothyroxine-only treatment, and preferred by patients.
A recent federally-funded study reported that NDT drugs are a safe and effective alternative to levothyroxine for thyroid hormone replacement.
There is also evidence that a subset of the population has a polymorphism — a genetic defect — called type 2 iodothyronine deiodinase. People with this genetic defect are less able to convert T4 to T3. Some researchers have found that these patients have better resolution of their hypothyroid symptoms when treated with combination T4/T3 therapy.
The main risks/side effects of thyroid hormone replacement medication come from overmedication. If you take too much thyroid medication you can have symptoms of hyperthyroidism, including nervousness, anxiety, insomnia, diarrhea, weight loss, high heart rate, and heart palpitations. When taken at the proper dose, however, levothyroxine typically has few side effects.
One occasional side effect of levothyroxine, however, is hair loss. Some patients find that changing brands of levothyroxine or switching from levothyroxine to NDT, may help alleviate this side effect.
Because T3 hormone is very short-acting and stimulatory, some people taking synthetic T3 tablets or NDT may have an increase in pulse rate or heart palpitations. For some patients, time-released compounded prescription T3 may help alleviate these side effects.
Taking your thyroid hormone replacement medication correctly
To ensure that you get the most benefit from your thyroid hormone replacement medication, here are some basic guidelines on how to take your medication correctly:
- Take your thyroid medication at the same time each day.
- Ideally, you should take your medication first thing in the morning, an hour before eating or drinking anything besides water.
- Wait for at least three to four hours after taking your thyroid medication before you take any supplements — including antacids — that contain iron or calcium
- Coffee and milk can both affect the absorption of thyroid medication, so wait at least an hour after taking your medication before drinking coffee (including decaf) and/or milk.
- Research has shown that taking levothyroxine at night may result in better absorption. It also allows you to eat, drink coffee, and take supplements first thing in the morning. If you have problems with absorption or scheduling, talk with your doctor about taking your medication at night.
An important note about storage of your thyroid medication
Thyroid medication can lose potency when exposed to moisture and heat. The best place to store your thyroid medication is a dry, cool area, not your bathroom or kitchen. Also, avoid leaving your thyroid medication for long periods in excessive heat, such as a hot mailbox, hot car, or away from air conditioning.
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Mary Shomon is a thyroid disease, hormonal and autoimmune health writer, and patient advocate. For two decades, Mary has been a leading force advocating for more effective, patient-centered thyroid and hormonal health care. Mary is the New York Times bestselling author of “The Thyroid Diet Revolution,” “Your Healthy Pregnancy with Thyroid Disease,” “Living Well With Hypothyroidism,” and 10 other books on thyroid disease and integrative health. She co-stars in two PBS health specials, “Healthy Hormones,” and “Vibrant for Life.” Follow her on Twitter at @thyroidmary or at her Facebook communities: ThyroidSupport and ThyroidDiet.