Podcast Summary: The Thyroid Fixer

Host: Dr. Amie Hornaman
Episode: 568 — How to ACCURATELY Test Your Thyroid: Timing Meds and Labs the Right Way
Date: October 10, 2025

Episode Overview

This episode tackles a crucial and often misunderstood part of thyroid management: When should you have your thyroid labs drawn if you’re taking thyroid medication? Dr. Amie Hornaman breaks down the science and dispels widely spread myths, using her expertise, personal experience, and a dose of tough love. The message is clear: proper timing of blood tests is essential for accurate results, correct medication adjustments, and actually feeling better.

Key Discussion Points & Insights

1. The Problem with Testing “At the Peak”

• Many practitioners advise testing thyroid labs (TSH, Free T4, Free T3, Reverse T3, antibodies) three to four hours after taking thyroid meds—so-called “peak” testing.
• Dr. Amie stresses there is no scientific documentation or functional medicine guidance supporting optimal lab values when tested at the peak.
  • Quote: “Any practitioner out there that's saying to test at the peak, they're pulling the numbers out of their ass.” (17:51)

Why peak testing is misleading:

• Numbers vary widely based on medication type, dose, and individual metabolism.
• Labs reflect recent medication in the bloodstream rather than the body’s actual usage and tissue saturation.
• The optimal functional range for Free T3 is valid only when tested 18–24 hours after last dose—not at the peak.

2. How Thyroid Medication Works in the Body

• T3 (liothyronine/Cytomel) peaks in the blood about 4 hours after ingestion, has a relatively short duration, but continues to be used by cells beyond 8 hours.
• Most protocols recommend split dosing of T3 to maintain levels, though exact timing varies individually (e.g., Dr. Amie takes T3 at 6am and 2pm).
• Taking labs at the peak gives artificially inflated Free T3 numbers, which can mislead clinicians into lowering T3 or adding T4 inappropriately.

Example Scenarios:

• Low dose T3: 10 mcg twice a day
  • Labs at peak: Free T3 may look “okay” (e.g., 6.0; lab range tops at 4.4), but 18–24 hours later, it could fall to 2.3, indicating under-treatment.
  • Quote: “If you just took your medication, you got a six. What's it actually going to be 18 to 24 hours from now? Like, that's probably going to be like a 2.3, which means you're highly undermedicated.” (28:40)
• High dose T3: Dr. Amie’s personal experiment with 75 mcg T3
  • Peak labs: Free T3 of 16
  • Practitioner might panic or drop dosage inappropriately, leading to weight gain or depression for the patient.
  • Quote: “Just dropping by 25 micrograms made me gain weight and changed my mood.” (36:08)
• Natural Desiccated Thyroid (NDT):
  • Typically 80% T4, 20% T3—peak testing may show “normal” Free T3, disguising true low state 18–24 hours later.

3. Guidelines for Correct Thyroid Lab Testing

• Free T3 should be measured 18–24 hours after your last dose of T3-containing medication.

  • This “trough” timing reflects the true level available to tissues, not a temporary surge.
  • The optimal functional range for Free T3 is the upper quadrant of the standard lab range.
    • (LabCorp range up to 4.4, so optimal might be 3.7–4.4+)
  • Always use the same time interval between last dose and blood draw for consistent comparison.

• If on T4 only (levothyroxine/Synthroid):

  • Timing is less critical because T4 has a long half-life, but skip the dose the morning of blood draw for maximal accuracy.
  • T4 can, but rarely, influence Free T4 labs if tested soon after dosing.

• Consistency is key:

  • Always aim for the same gap (in hours) between last medication and blood draw for every test to enable apples to apples result tracking.
  • Quote: “Pick a time, and that time is...the same gap every single time you get labs. So if you're testing at the 18 hour mark this time, then next month...go 18 hours.” (01:21:30)

4. What Can Go Wrong with Improper Timing

• Testing at the peak can:

  • Mask under-medication (looks good on paper, patient still symptomatic)
  • Lead to unnecessary reduction of T3, inappropriate T4 increases, causing worsening symptoms or depression
  • Result in poor medical decisions due to misleading lab values
  • Produce non-comparable results across tests due to timing inconsistency

• Dr. Amie’s bottom line: “This is basic biology, basic science...Now it makes no sense whatsoever to test at the peak.” (01:01:30)

5. Drawing Parallels — Other Hormones

• Similar principle applies to testing after dosing with testosterone, estrogen, or progesterone: labs will reflect recent dosing, not true, steady-state body levels.
• “If you take a shot of testosterone and...the next day...you're going to have an abnormal high number…You're getting the medication or that hormone picked up in your bloodstream.” (57:00)

Notable Quotes & Memorable Moments

• On practitioner misinformation:
  • “There is nowhere…in any kind of functional medicine training, there’s no functional optimal range for testing your thyroid values [at the peak].” (14:31)
• Challenging the status quo:
  • “That peak number of free T3 is going to vary based on the medication dose…Who’s right? Who’s optimal? Who’s over medicated? You can’t tell.” (01:07:20)
• Patient empowerment:
  • “If someone…wants to test your T3 at the peak, you could be like, oh my God, no, no!...Test appropriately so you know your numbers.” (01:27:20)
• Consistency as strategy:
  • “If you can nail the time exactly, not a big deal. What we end up doing is…look at through that optimal lab value range.” (01:21:00)
• Symptoms trump numbers:
  • “If you tell me you feel like a rockstar…am I going to change your dose? No, I’m not.” (01:15:00)

Key Timestamps

• [14:31] — No functional medicine guidelines endorse “testing at the peak.”
• [17:51] — “Pulling the numbers out of their ass”—calling out bad advice.
• [28:40] — How lab values change based on timing of blood draw.
• [36:08] — Dr. Amie’s personal medication experiments and consequences.
• [57:00] — Analogy with other hormone therapies (testosterone).
• [01:01:30] — “This is basic biology, basic science…light bulb moment.”
• [01:07:20] — No optimal free T3 at peak; individual variability.
• [01:15:00] — “If you feel good…we’re not touching it.”
• [01:21:00] — Consistent timing for lab draws is crucial.
• [01:27:20] — Real-life patient scenario: improper testing, poor outcome.
• [01:28:30] — Final takeaways and encouragement to join the community.

Episode Takeaways

1. Always schedule your thyroid labs 18–24 hours after your last T3-containing dose.
2. Use the “upper quadrant” of the lab range for Free T3 as your optimization target—but only with proper timing.
3. Symptoms matter more than just numbers—feel good? Then you're likely on the right track.
4. Be consistent with timing across all tests for proper tracking.
5. Push back against practitioners who want to test at the peak or interpret labs without considering timing.

Community Resource

Dr. Amie encourages listeners to join her Just Fix Your Thyroid Facebook group for free Q&As, patient-sharing, and personalized support—described as a supportive, knowledgeable, and badass community.

Summary:
Dr. Amie’s episode is a must-listen for anyone who takes thyroid medication. Her bottom line: Testing at the wrong time will only set you back. Empower yourself with the science, insist on correct lab timing, and use your own symptoms as the best guide to optimizing thyroid health.