Top 11 Things You Need To Know About Thyroid Medications

By Dr. Izabella Wentz, Pharm D

If you’re taking thyroid medications and still not feeling well, be sure to read this entire post.


  1. Types of Thyroid Medications: Synthroid was the most commonly prescribed medication in the United States in 2013, but it isn’t the only thyroid medication (2014 data will be out soon and it looks like Synthoid is in the lead this year as well). There are three types of medications that can be used to treat underactive thyroid: T4 containing medications (include Synthroid, Levoxyl, Levothyroxine and Tirosint), T3 containing medications (Cytomel ***may be cross-contaminated with gluten*** and compounded T3) and combination T4/T3 medications (Armour, Nature-Throid, WP Thyroid, compounded T4/T3 medications). Some people with Hashimoto’s, may not be able to properly convert levothyroxine (T4), the active ingredient in Synthoid, to liothyronine (T3), the more metabolically active thyroid hormone, leading to unresolved thyroid symptoms, including fatigue, depression, weight gain and hair loss, despite being on medications. For more information on various thyroid medication options, here’s an article I wrote: Which Thyroid Medication is Best?
  2. Medication Monitoring: Thyroid medications are “goldilocks” hormones, which means that they have a narrow therapeutic index. They are dosed in micrograms (1/1000th of a milligram), and very slight changes in doses can lead to symptoms due to under-treatment or over-treatment. The most common side effects of the medications such as the ones listed in the package insert are often due to over-treatment (rapid or irregular heartbeat, chest pain, irritability, nervousness, insomnia, weight loss, diarrhea, excessive sweating, ) or under treatment (hair loss, fatigue). Careful dosage titration is necessary to avoid the consequences of over- or under-treatment. In addition to tracking your symptoms, you should have the following  tests done: TSH, Free T3 and Free T4 to monitor your response to medication. While reference ranges of what’s “normal” may vary depending on the lab that produces the test reports, most thyroid patients feel best with a TSH between 0.5-2, and with Free T3 and Free T4 in the top half of the reference range. Postpone your thyroid medications on the morning of the test-some medications (esp. T3 containing medications) may skew your numbers.

    For a symptom tracker and a letter to your doctor about medication adjustments, see my article: When Your TSH is Normal But You Are Anything But

  3. Switching Medications: Switching between brands of thyroid medications, though sometimes necessary, can mean that a person who was previously stable on a particular dose of medication may require a higher or lower dose of the new brand. Retest your thyroid 4-8 weeks after switching from one brand of medication or dose increases to be sure you are dosed appropriately. For more information read my article Switching Thyroid Medications
  4. Thyroid Drug Interactions: Thyroid medications are notorious for drug interactions with other medications. This means that some medications can cause alterations in thyroid hormone levels and side effects, and in turn, thyroid medications can impact the effectiveness and toxicity profiles of other medications. Always be sure to check with your pharmacist when taking new medications or over the counter drugs. Ideally, you should fill all of your prescriptions at the same pharmacy so your pharmacist can do a check of your drug interactions every time you fill a prescription.
  5. Addison’s Disease and Thyroid: Always be sure you are tested for Addison’s disease before starting on thyroid hormones. Addison’s disease is an autoimmune condition that affects the adrenal glands.  Starting thyroid medications in someone who has untreated Addison’s disease can cause an increased clearance of glucocorticoids, hormones that are usually deficient in Addison’s resulting in a life threatening reaction. 17-hydroxylase antibodies.
  6. Pregnancy and Thyroid: Thyroid medications are Pregnancy Category A, which means that they are considered to be safe medications for using during pregnancy. Being on a correct dose of thyroid medication can actually help women conceive as well as prevent miscarriage. If you get pregnant while taking thyroid hormones, be sure to see your doctor ASAP to test your levels. You will very likely need to increase your dose, as pregnancy increases the requirement of thyroid hormones. If you are thinking about pregnancy, be sure to read this guest post Hashimoto’s and Pregnancy
  7. Fillers in Medications: Some people may react to fillers in Synthroid (corn starch, confectioners sugar, lactose, magnesium stearate, povidone, talc and color additives). People who are lactose intolerant, in particular may have trouble absorbing many of the thyroid hormones that contain lactose. Tirosint is a new thyroid medication that does not contain lactose and may prove to be a better option for those with lactose intolerance (article on lactose intolerance and thyroid coming soon). In the mean time, you may want to read my article Which Thyroid Medication is Best?
  8. Absorption (External Factors): Thyroid medications absorption can be impacted by many things, including food, other medications and supplements. Thyroid medication should be taken on an empty stomach, 30 minutes to one hour before eating, taking other medications, supplements or coffee to ensure appropriate absorption. Antacids such as Tums, iron and calcium supplements can impair the absorption of thyroid medications. Thus, you need to have at least 4 hours of time in between your thyroid medications and these agents.
  9. Absorption (Internal Factors): Thyroid hormones are absorbed in the small intestine. Conditions like untreated celiac disease, lactose intolerance, malabsorption and infections in the small intestine may prevent proper thyroid hormone absorption. A person who is not responsive to the usual doses of thyroid replacement hormone should be investigated and treated for the above listed condition. Once someone addresses these conditions, she/he may need to have a dose reduction in medication.

    Read more about gluten and optimizing your diet in my article on Best Diet For Hashimoto’s

  10. Prognosis: Thyroid medications are generally considered lifelong for most cases of hypothyroidism, but spontaneous remission has been reported to occur in up to 20% of patients… however addressing root causes can help increase the rates of remission. If you do not address the underlying root causes of your condition, your own thyroid’s hormone production may deteriorate over time, meaning that you may require dose increases over time. Symptoms of worsening thyroid function can sometimes be subtle (such as gaining a little extra weight every year, or being just a tad bit more tired), so you will need to test your thyroid function labs at least every 6-12 months to monitor your thyroid hormone levels.

    For more information see the following articles:  6 Hashimoto’s Root CausesAre Thyroid Medications Lifelong?

  11. Beyond Medications: There’s a lot more to healing thyroid disease than medications. Most causes of thyroid disease, are due to autoimmune conditions including Hashimoto’s and Graves’ disease. These conditions result from the immune system attacking the thyroid because the immune system is out of balance. Even when the thyroid is taken out surgically or treated with radioactive iodine the autoimmunity still persists in most cases. Additionally, people with thyroid disorders are at greater risk to develop new autoimmune disorders such as Lupus, Rheumatoid arthritis and others if they do not treat the underlying cause of the immune imbalance. Most times, it’s a combination of adrenal dysfunction, food sensitivities, nutrient deficiencies, impaired gut function, infections and toxins that lead to the development of autoimmune disease. In addition to discussing proper thyroid medication dosing, the majority of my website and my book, Hashimoto’s: The Root Cause focuses on balancing the immune system. The info I present is based on my own research in journey for overcoming my autoimmune thyroid condition.

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