Your Thyroid Gland and Why You May Need to Add T3 to Your T4 Medication



The thyroid gland uses iodine from the foods you eat to produce two main hormones, triiodothyronine (T3) and thyroxine (T4). T3 and T4 control your body's metabolism. If you don't have enough of them, your metabolism slows down. This impacts how quickly you digest and process food, how fast your heart beats, how much heat your body creates, and even how quickly your mind works. Essentially, T3 and T4 are in charge of how your body uses energy.


It is important that T3 and T4 levels are neither too high nor too low. Two glands in the brain—the hypothalamus and the pituitary communicate to maintain T3 and T4 balance.


If you have too little T3 and T4 in your body (hypothyroidism), you may experience these symptoms:


  • Trouble sleeping

  • Tiredness and fatigue

  • Difficulty concentrating

  • Difficulty with weight loss, gaining weight despite exercising and dieting

  • Constipation

  • Dry skin and hair

  • Depression

  • Sensitivity to cold temperature

  • Frequent, heavy periods

  • Joint and muscle pain


T3 and T4 are not equal in strength; T3 is the more active hormone of the two. While T3 is stronger, taking synthetic T4 hormone is considered the standard treatment for hypothyroidism. The reason for this is because most of the T3 in our bodies actually used to be T4. The normal thyroid gland produces about 80% T4 and about 20% T3, so the majority of T3 is converted peripherally from T4 by the liver and other tissues of the body. T4 also lasts longer in the body.


Thus, most conventional treatment for hypothyroidism is to prescribe levothyroxine (i.e. Levoxyl, Synthroid), which is a T4 replacement. However, many people have trouble converting T4 to T3 due to a number of factors including physical and emotional stress, mineral status like zinc and selenium, and iron stores. An imbalance in these areas can increase the production of reverse T3, which is inactive thyroid hormone. This is also converted from T4, so the higher the levels of reverse T3, the lower the levels of normal, active T3. This decreases the overall activity of thyroid hormone, impacting metabolism.


Many patients coming to me who have been on T4 for long periods of time are still feeling fatigued, have trouble with weight gain, feel cold, etc, even with their TSH levels being “normal”. Often, this is because T3 levels are low despite having decent T4 levels, showing a conversion issue. In these cases, it is very helpful to add in some external T3 while also working on trying to improve the conversion process. I add in some T3 either through 1) switching to a natural, dessicated thyroid product like Nature-throid, or 2) adding in synthetic T3 to the T4 medication that a person is already taking. There are many approaches around dosing and medications. I usually like to start with Nature-throid in hypothyroid patients that are first diagnosed and or are switching from a straight T4 medication. Else, I often also add synthetic T3 to a patient’s T4 medication, especially in patients who have autoimmune thyroiditis (Hashimoto’s) or have already tried Nature-throid and are not doing great with it. When adding in T3 to a T4 medication, I like to use a sustained release T3 that is compounded, as it is absorbed into the body at a slower rate and does not wear off as quickly as normal T3, which is released rapidly and can sometimes cause more side effects such as heart palpitations, anxiety, sweating, and headaches.


Most patients do best with a combination of T3 and T4, whether it is in a synthetic or natural form. If you or someone you know has hypothyroidism or Hashimoto’s and is still struggling with symptoms of hypothyroidism with or without medication, please have them contact us. They may need to start or adjust their medication, as well as giving their thyroid gland more support.

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