Dedication
With deep appreciation, this book is dedicated to the memory of the late Dr. Raymond Franklin Peat (1936–2022).
Dr. Ray Peat was a distinguished American scholar with a Ph.D. in biology who devoted much of his life to exploring the intricate connections among metabolism, thyroid function, nutrition, hormones, health, and longevity.
His groundbreaking work in the fields of metabolism, hypothyroidism, aging, fertility, PMS, menopause, and related topics has profoundly impacted the health of countless individuals, including myself.
Dr. Peat viewed optimal thyroid function as a cornerstone of good health and longevity. He contended that the conventional reference ranges for thyroid blood tests are overly broad, causing many individuals with hypothyroidism to remain undiagnosed. Consequently, these individuals continue to suffer from symptoms of hypothyroidism that could be alleviated through accurate and targeted thyroid treatment.
Through his in-depth research, Peat looked at the most effective dietary approaches for supporting metabolism and thyroid health. He also explored the best thyroid hormone replacement therapies and emphasized the importance of related hormones, such as natural progesterone and pregnenolone, in achieving complete metabolic and hormonal balance.
The Healing Metabolism book series explores various aspects of Dr. Peat’s health philosophy. This book aims to provide a thorough yet easy-to-understand explanation of his thyroid medication protocol for treating hypothyroidism, including Hashimoto's disease, utilizing T4, T3, natural desiccated thyroid (NDT), and adrenal support.
Benedicte Mai Lerche, MSc, PhD
August 2025
Introduction
In my early twenties, I faced severe hypothyroidism, also known as low thyroid function. I struggled with debilitating symptoms, including chronic fatigue, headaches, severe digestive pain, allergies, muscle aches, brain fog, menstrual disturbances, and more.
Desperately seeking effective treatment, I embarked on a transformative journey that profoundly changed my life. Initially, the doctors were unable to identify any underlying cause for my numerous symptoms. When I finally got diagnosed with hypothyroidism, finding the proper treatment also proved to be quite difficult. My breakthrough came when I discovered Dr. Peat’s work. His research, expertise, and personal guidance became a crucial turning point in my fight against hypothyroidism, giving me the knowledge I needed to regain my health.
Thyroid function is controlled by the thyroid gland, which produces two hormones: thyroxine (T4) and triiodothyronine (T3). T3 is the active hormone, while T4 acts as a precursor that can be converted into T3. The active T3 hormone manages the body's metabolism, the process by which food is turned into energy. As a result, T3 plays a crucial role in regulating the body’s energy production.
In hypothyroidism, T3 levels are low, leading to reduced energy production and a range of symptoms as the body's tissues and organs have difficulty functioning properly in this energy-deficient state.
Although severe hypothyroidism is usually diagnosed, many individuals have milder forms of the condition without receiving a formal diagnosis. This is partly because the reference ranges for thyroid blood tests are quite broad. As a result, many people may have normal test results despite experiencing symptoms of hypothyroidism.
Typically, hypothyroidism, including the autoimmune condition known as Hashimoto's thyroiditis, is treated with synthetic T4, also called levothyroxine. An alternative is combination therapy, which uses both T4 and T3, either in synthetic form or as natural desiccated thyroid (NDT).
This book offers a comprehensive review of thyroid hormone replacement therapy, commonly referred to as thyroid medication. I will cover various treatment options and explain why Dr. Peat favored a combination of T4 and T3, with a high ratio of T3. Emphasizing T3 is essential because it is the active form of thyroid hormone that functions at the cellular level.
It is common for people starting thyroid medication to feel worse as they try to increase their dosage. These negative symptoms are often blamed on weak adrenals, commonly called "adrenal fatigue.” This book provides a thorough look at the connection between thyroid function and the adrenals, explaining how Dr. Peat used natural hormone supplements like progesterone and pregnenolone to support the adrenals and reduce the negative symptoms that can occur when increasing the metabolic rate with thyroid medication.
He also emphasized the importance of adopting a pro-metabolic diet and implementing additional lifestyle changes to support the entire thyroid system, which includes the thyroid gland, the T4-to-T3 conversion process, and the cellular response to the active thyroid hormone T3.
Peat took the time to explain all aspects of his health approach to me. I followed his thyroid medication protocol, which provided clear instructions on the proper use of thyroid hormones. I also learned to track my metabolic response to the medication by monitoring my body temperature and pulse rate. Additionally, he taught me how to adopt a balanced diet and lifestyle to boost my metabolism and support my thyroid health. Dr. Peat explained that an improper diet can undermine the effects of even the best thyroid medication, emphasizing that pro-metabolic food choices are essential for effectively treating hypothyroidism, including Hashimoto's thyroiditis.
Dr. Peat’s health approach quickly made me feel significantly better, and within a few months, my symptoms disappeared. Since then, I have continued to follow his health philosophy and still enjoy a vibrant life filled with energy, free from hypothyroid symptoms.
Inspired by my recovery, I pursued a degree in biochemistry at university. Over the years, I kept in touch with Dr. Peat and followed his research with great interest.
I founded my website, biochemnordic.com, where I offer online video counseling and e-learning, helping individuals implement Dr. Peat’s health philosophy.
The sad passing of Dr. Peat in 2022 inspired me to create my book series, “Healing Metabolism.” To share Dr. Peat’s valuable insights widely, each volume covers different facets of his pro-metabolic health approach. This current book focuses specifically on his thyroid medication protocol, guiding readers through the often-complex process of using thyroid hormones effectively. It is helpful for individuals with hypothyroidism, including those with Hashimoto’s thyroiditis, and for people seeking to enhance their metabolic rate with over-the-counter thyroid glandular supplements. Additionally, this book is essential for individuals who have had their thyroid gland removed and are therefore relying on optimal thyroid medication for the rest of their lives.
The book is structured as follows:
Chapter 1:
This chapter explains the function of the thyroid gland, including how it produces and secretes thyroid hormones. You will learn how TSH regulates the levels of T4 and T3, and how T4 is converted to T3 in the liver and other organs and tissues. You will understand the importance of the active thyroid hormone T3 for maintaining the body's proper structure and function, as well as its vital role in metabolism and energy production.
Chapter 2:
This chapter explores hypothyroidism, highlighting the many symptoms associated with an underactive thyroid. It also discusses Dr. Peat's perspective on the autoimmune form of hypothyroidism, particularly Hashimoto's thyroiditis, which greatly differs from mainstream views. Additionally, the chapter considers his insights into the various causes and triggers of hypothyroidism.
Chapter 3:
This chapter discusses diagnosing hypothyroidism. You will learn about the wide reference ranges for thyroid blood tests, highlighting that hypothyroidism can still be present even if lab results fall within the "normal" range. Additionally, you will learn how to monitor metabolism at home using body temperature and pulse rate, which is crucial for tracking your metabolic response to thyroid medication.
Chapter 4:
This chapter provides a detailed examination of thyroid medication. You will learn about the history of thyroid treatments and why T4 monotherapy can be problematic, especially for those who struggle to convert T4 to T3. The chapter also discusses the use of T3 in treating hypothyroidism and explores combination therapy with both T4 and T3. It explains the confusion surrounding the ideal T4-to-T3 ratio in combination therapy and outlines Dr. Peat's recommendation for a higher T3 proportion. Additionally, the chapter compares therapy using synthetic thyroid hormones to that of natural desiccated thyroid (NDT).
Chapter 5:
This chapter details Dr. Peat's thyroid medication protocol, including advice on choosing the best type of thyroid medication. You will learn the typical daily dosage for adults and get clear guidance on how to properly use thyroid hormones, with special instructions for T3 since this hormone is very active and can cause problems if misused. You will discover how to start thyroid medication and gradually increase your dosage while monitoring your pulse and temperature to find your ideal maintenance level. The chapter also answers common questions, such as whether thyroid medication is lifelong or how to safely stop the medication if you decide to. Additionally, it discusses the safety of using T3 during pregnancy and explains why some people need large dosages of thyroid medication but experience minimal effects. The chapter also covers foods and substances that can suppress thyroid health and interfere with the effectiveness of your thyroid medication.
Chapter 6:
This chapter examines the truth about adrenal fatigue, emphasizing how both weak and overactive adrenal glands can cause complications when starting thyroid hormone therapy. It discusses Dr. Peat’s advice on using progesterone and pregnenolone to support the adrenals and mitigate the negative symptoms that some individuals experience when increasing their thyroid dosage.
Chapter 7:
The final chapter summarizes the key points about thyroid medication covered in this book, highlighting how Dr. Peat’s protocol stands apart from conventional approaches. Furthermore, this concluding chapter offers a broader perspective on his pro-metabolic diet and lifestyle recommendations, underscoring the necessity of incorporating additional health strategies beyond thyroid medication to enhance metabolism and address hypothyroidism, including Hashimoto's thyroiditis. Ultimately, this chapter acts as a stepping stone for those looking to explore Dr. Ray Peat's methodologies further in future readings and resources available on my website, biochemnordic.com.
Chapter 1: Thyroid Function
The Thyroid Gland
Positioned at the front of the throat, the human thyroid gland (Figure 1) is butterfly-shaped and functions as a vital endocrine (hormone-producing) organ. It measures about 2 inches (5 cm) wide and weighs between 20 and 60 grams (Richard N. Fogoros, 2024; Barnes & Galton, 1976, p. 3; InformedHealth.org, 24).
Figure 1: A diagram of the human thyroid gland, showing its unique butterfly shape and position at the front of the throat.
As a key component of the endocrine system, the thyroid influences the functions of other endocrine glands, including the adrenal glands, pancreas, ovaries, and testes (Barnes & Galton, 1976, p. 20).
The thyroid gland produces and secretes two hormones: triiodothyronine (T3) and tetraiodothyronine (thyroxine, T4), which are collectively known as the thyroid hormones (Society of Endocrinology, 2020; Vander, et al., 2001, p. 267).
The thyroid gland also produces a small protein known as calcitonin, which is involved in calcium and bone metabolism (InformedHealth.org, 24; Vander, et al., 2001, p. 266).
The defining feature of thyroid hormones is their iodine content. T3 contains three iodine atoms, while T4 contains four iodine atoms (see Figure 2) (Richard N. Fogoros, 2024; Vander, et al., 2001, p. 267).
Figure 2: Chemical structure of the two thyroid hormones.
The thyroid gland contains many tiny round sacs known as follicles, which produce, store, and release thyroid hormones (Canadian Cancer Society, 2021; Vander, et al., 2001, pp. 266-267).
To synthesize thyroid hormones, the amino acid tyrosine and iodine must be combined under appropriate conditions (McGavack, 1951, p. 76).
Iodine from our diet is absorbed through the gastrointestinal tract and travels through the bloodstream to the thyroid gland, where the follicles take it up. In the follicles, iodine combines with tyrosine to first form monoiodotyrosine (T1) or diiodotyrosine (T2). These compounds are then combined to produce either triiodothyronine (T3) or thyroxine (T4). The process of thyroid hormone synthesis is mediated by the enzyme thyroid peroxidase (TPO) (Vander, et al., 2001, p. 267; Armstrong, et al., 2023; Canadian Cancer Society, 2021; McGavack, 1951; Gomes-Lima, 2018; Science direct, 2024).
T1 + T2 = T3
T2 + T2 = T4
Inside the thyroid follicles, T4 and T3 are stored bound to a protein called thyroglobulin (Tg). During the secretion of thyroid hormones from the thyroid gland, thyroglobulin is broken down, releasing T4 and T3 into the bloodstream (Vander, et al., 2001, pp. 266-267).
T3 is the active thyroid hormone that impacts cells, while T4 serves as a prohormone for T3. Once secreted by the thyroid gland, T4 can be converted into T3 in various organs and tissues (Society of Endocrinology, 2020).
It is known that the thyroid gland secretes significantly more T4 than T3. However, researchers have not reached a consensus on the precise amounts of T4 and T3 secreted daily (Vander, et al., 2001, p. 267).
The amounts of these hormones are typically expressed on a weight basis. Due to the very small quantities of hormones released, the measurement unit is micrograms, which equals one-millionth (1/1,000,000) of a gram. Micrograms can be represented as either µg or mcg. In this book, I will refer to it as mcg (Wiersinga, et al., 2012).
Those with hypothyroidism are typically treated with thyroid hormones to compensate for what their thyroid gland fails to produce. Since the 1970s, the standard treatment has been monotherapy with synthetic T4, also known as levothyroxine. However, recent studies suggest that some people with hypothyroidism may benefit from combination therapy that includes both T4 and T3 (McAninch, 2016).
Combination therapy generally aims to mimic the natural hormone secretion of a healthy human thyroid gland (Wiersinga, et al., 2012).
According to Dr. Peat, the healthy thyroid gland produces about the equivalent of four grains of natural desiccated thyroid (NDT) each day (Ray Peat emails, 2024a).
One grain of NDT is said to contain a 4:1 ratio of T4 to T3, with one grain corresponding to approximately 38 mcg of T4 and 9 mcg of T3. Therefore, four grains would provide approximately 152 mcg of T4 and 36 mcg of T3. Dr. Peat clarified that the ratio of T4 to T3 found in NDT and secreted by a functioning human thyroid gland is actually closer to 3:1 (Ray Peat emails, 2024a; Peat, 2000; Peat, 2001a, p. 73)
So, it is okay to use thyroid medications that have a T4-to-T3 ratio of around 3:1 or 4:1. According to Dr. Peat, a 3:1 ratio is often the best choice, as many people notice their memory and thinking are clearer when they stick to this T4-to-T3 ratio (Peat, 2000).
Conversely, some researchers advocate for a significantly lower proportion of T3 in combination therapy, based on their belief that the human thyroid gland naturally produces only minimal amounts of T3 (Wiersinga, et al., 2012, p. 56; Wiersinga W. M., 2021; Jonklaas, et al., 2014).
Because researchers continue to debate the exact daily amounts of T4 and T3 secreted by the functioning human thyroid gland, differing views exist on the optimal T4-to-T3 ratio for combination therapy (Sapin, 2003; Cleveland Clinic, 2022; Shahid MA, 2024; Robert M. Sargis, M.D., Ph.D., 2019; Richard N. Fogoros, 2024; Wiersinga, et al., 2012; Jonklaas, et al., 2014; Shomon, 2021a).
I will revisit the ongoing debate about the T4-to-T3 secretion ratio of the healthy human thyroid gland in Chapter 4, which examines various approaches to thyroid medication. Additionally, as this book centers on Dr. Peat’s thyroid medication protocol, special emphasis will be placed on his perspective regarding this topic.
Interplay of TSH, T4, and T3
The levels of T4 and T3 in the blood are regulated by thyroid-stimulating hormone (TSH) (Vander, et al., 2001, p. 280).
The pituitary gland in the brain produces TSH, which stimulates the thyroid gland to produce and release more thyroid hormones into the bloodstream (Society of Endocrinology, 2020).
TSH and the thyroid hormones function within a negative feedback loop, as illustrated in Figure 3 below. When blood levels of T4 and T3 are sufficient, TSH secretion remains low. However, if T4 and T3 levels drop, TSH secretion increases (Vander, et al., 2001, p. 281).
It may seem logical to assume that the body could utilize this feedback loop to correct hypothyroidism by increasing TSH levels, thereby stimulating the thyroid gland to produce more hormones. Indeed, TSH levels are usually raised in hypothyroidism. However, it’s essential to acknowledge that TSH itself possesses pro-inflammatory properties. Dr. Peat explained that many of the symptoms of hypothyroidism are directly caused by the elevated TSH itself (Ray Peat, Clips, 2016b; Peat, 2008, p. 2; Ray Peat Clips, 2016c).
Moreover, chronic overstimulation of the thyroid gland by TSH can result in inflammation and structural disorganization within the gland (Peat, 2000, p. 2).
A blood test measuring TSH is frequently used to evaluate thyroid function, with elevated TSH levels indicating hypothyroidism (Vander, et al., 2001, p. 281; Peat, 2008, p. 2). Further details on the TSH blood test will be provided in Chapter 3.
Figure 3. Illustration of the relationship between TSH and the thyroid hormones T4 and T3. The first image shows how low levels of T4 and T3 cause TSH to rise. On the other hand, the second image demonstrates that optimal levels of T4 and T3 lead to a decrease in TSH.
Conversion of T4 to T3
The thyroid gland is the only producer of T4 in the body. T4 is inactive by itself but acts as a storage hormone—or prohormone—for T3 (Vander, et al., 2001, p. 267).
After the thyroid gland releases T4, it can be converted into the active hormone T3 in various organs and tissues. This process is known as peripheral conversion, which indicates that the conversion occurs outside the thyroid gland itself (Alan Jacobs, 2023; Gomes-Lima, 2018)
Most of this peripheral conversion takes place in the liver, making the liver essential for regulating the body's T3 level (Peat, 2001a, p. 73; Josh Redd, 2020).
According to Dr. Peat, the body produces approximately 100 mcg of T3 each day. Some of the T3 is secreted directly by the thyroid gland, while the majority is generated through peripheral conversion. Dr. Peat noted that about 70% of the T3 produced daily comes from the liver’s conversion of T4 to T3 (Peat, 2001d, p. iv; Raymond Peat, 2022).