What Is Reverse T3 (rT3)?
Reverse T3 (rT3) is an inactive form of thyroid hormone that the body produces when it converts T4 (thyroxine) into T3 (triiodothyronine). While T3 is the active hormone responsible for regulating metabolism, energy, and body temperature, rT3 acts like a “brake”—slowing things down when needed.
This conversion is regulated by enzymes called deiodinases. Under normal circumstances, most T4 is converted to active T3 through DIO1 and DIO2 enzymes. However, during times of stress, illness, or nutritional deficiency, the body increases conversion of T4 into rT3 via DIO3, reducing active thyroid hormone levels.
🔗 Learn more about T4 to T3 conversion – American Thyroid Association
Why Does Reverse T3 Matter?
High rT3 levels can block thyroid hormone receptors, preventing active T3 from doing its job—even when TSH, T4, and T3 levels appear normal on standard blood tests. This can lead to hypothyroid-like symptoms despite “normal” labs.
Common Causes of Elevated Reverse T3
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Chronic Stress – High cortisol levels boost rT3 production.
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Illness or Inflammation – Infections, surgeries, or autoimmune conditions like Hashimoto’s can increase rT3.
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Nutrient Deficiencies – Low levels of iron, selenium, zinc, or vitamin B12 impair T4-to-T3 conversion.
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Extreme Dieting – Very low-calorie or low-carb diets push the body to conserve energy by producing more rT3.
🔗 How stress affects thyroid function – Harvard Health Publishing
Symptoms of High Reverse T3
You may experience symptoms that mimic hypothyroidism, including:
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Constant fatigue, even with good sleep
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Weight gain or inability to lose weight
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Brain fog, forgetfulness, or depression
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Cold hands and feet
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Hair thinning or brittle nails
🔗 Hypothyroidism vs. high rT3 – Cleveland Clinic
How to Lower Reverse T3 Naturally
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Reduce Stress – Try meditation, yoga, breathing exercises, or time in nature to reduce cortisol.
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Improve Nutrition – Ensure you’re getting enough iron, selenium, zinc, and B vitamins (especially B12).
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Avoid Crash Dieting – Stay away from long-term fasting or extreme low-carb diets.
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Treat Root Causes – Address any infections, gut health problems, or autoimmune conditions.
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Get Proper Testing – A full thyroid panel should include TSH, Free T3, Free T4, and rT3 to give a complete picture.
🔗 Best foods for thyroid health – WebMD
When to See a Doctor
If you’re experiencing thyroid-related symptoms but your TSH and T4 are normal, ask for reverse T3 testing. A functional medicine practitioner or thyroid-savvy endocrinologist can help interpret your labs and create a personalized plan.
🔗 Find a thyroid specialist – American Association of Clinical Endocrinologists
Final Thoughts
Reverse T3 serves a protective role during times of stress or illness—but when elevated long-term, it can block your metabolism and energy levels. By managing stress, supporting nutrition, and addressing root causes, you can restore healthy thyroid function and start feeling like yourself again.
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