The Role of Thyroid Hormones in Your Body
T4 (Thyroxine)
The primary hormone, which is converted into the active form, T3, in different parts of the body.
T3 (Triiodothyronine)
The hormone that actively affects metabolism, impacting how the body uses energy.
Together, T4 and T3 control the body’s metabolism, which keeps essential functions like heart rate, temperature, and energy levels running smoothly. When the thyroid doesn’t produce enough of these hormones, metabolic processes slow down.
Common Symptoms of Hypothyroidism
Symptoms of hypothyroidism can vary widely, but 60% of those affected are unaware they have the condition.2
Know What to Look for
Fatigue
Weight Gain
Cold Intolerance
Memory Loss
Hair Loss
Low Libido
Constipation
Depression
Dry Skin
Heavy or Irregular Menstrual Periods
When Things Slow Down
How Your Thyroid Works – Or Doesn’t Work
The thyroid is part of the endocrine system, and its activity is controlled by the pituitary gland in the brain.
This is how the process works:
- The Pituitary Gland releases thyroid-stimulating hormone (TSH) to signal the thyroid to produce hormones.
- The Thyroid Gland then produces two key hormones:
- T4 (Thyroxine): The primary hormone released by the thyroid, which serves as a reservoir that must be converted into an active form.
- T3 (Triiodothyronine): The active hormone that regulates metabolism, energy levels, and other key functions. Most T3 comes from the body converting T4 into T3 in organs like the liver and kidneys.
However, in people with hypothyroidism, the thyroid doesn’t produce enough T4, or the body struggles to convert T4 into the active T3. As a result, metabolism slows down, leading to symptoms like fatigue, brain fog, and low energy.
[1] Wyne KL, Nair L, Schneiderman CP, et al. Hypothyroidism Prevalence in the United States: A Retrospective Study Combining National Health and Nutrition Examination Survey and Claims Data, 2009-2019. J Endocr Soc. 2022;7(1):bvac172. Published 2022 Nov 10. doi:10.1210/jendso/bvac172
[2] American Thyroid Association. General Information/Press Room. American Thyroid Association website. Accessed April 18, 2025. https://www.thyroid.org/media-main/press-room/?_ga=2.79223063.2011195064.1724265032-207686090.1723645594%E2%80%8B
USE:
RenThyroid™ (Thyroid Tablets, USP) is a prescription oral medication used to replace or supplement thyroid hormones in patients with hypothyroidism from any cause, except transient hypothyroidism during the recovery phase of subacute thyroiditis.
- RenThyroid should not be used for male or female infertility unless this condition occurs with low thyroid levels.
- Taking too much RenThyroid may affect your cardiovascular system, especially if you are elderly or have heart problems. Tell your doctor immediately if you have any signs of chest pain, increased pulse, palpitations, excessive sweating, or any other unusual event.
- Tell your doctor about any other medical conditions you may have, especially heart disease, diabetes, blood clotting problems, and adrenal or pituitary gland problems. The dose of other drugs you may be taking for these conditions may have to be changed while you are taking RenThyroid. If you have diabetes, monitor your blood sugar levels and/or the glucose in your urine, and immediately tell your doctor if there are any changes.
- Tell your doctor about all of the medicines you take, including prescription and over-the-counter medicines, vitamins and supplements. Especially tell your doctor if you take anticoagulants, diabetes drugs, oral contraceptives, or biotin.
- In infants, excessive doses of RenThyroid may cause a condition called craniosynostosis (premature closure of the skull bones).
- In children, partial hair loss may occur during the first few months of taking RenThyroid.