Functional medicine practitioners often look at thyroid symptoms through diet, specific nutrients, gut health, toxin exposure and stress, alongside lab tests. Mainstream thyroid guidance is narrower. TSH is the first test, levothyroxine is the standard treatment for an underactive thyroid (hypothyroidism), and alternatives such as desiccated thyroid, combination T3 therapy and selenium have limited evidence. If you're considering functional medicine for a thyroid condition, the safest route keeps your prescribing doctor involved and treats any add-ons as additions, not replacements.
How functional medicine approaches the thyroid
The Institute for Functional Medicine (IFM) describes levothyroxine as the conventional treatment for low thyroid function. Its functional approach adds attention to (IFM, updated August 2026):
- diet and lifestyle, including anti-inflammatory diets;
- specific nutrients, including iodine and iron, which IFM calls crucial for making thyroid hormone;
- gut health, toxin exposure and stress;
- factors that IFM says shift T4 toward reverse T3.
IFM's article doesn't recommend stopping levothyroxine. It cites one small trial (60 people) in which a synbiotic supplement was linked to lower TSH and a lower levothyroxine dose, and it notes that experts disagree on how to handle mild (subclinical) hypothyroidism.
Testing: what guidance says
Standard thyroid tests
The American Thyroid Association (ATA) says TSH is the best first test, and advises measuring free T4 with it (ATA, thyroid function tests). MedlinePlus lists TSH, T3, T4 and thyroid antibody tests for diagnosing hypothyroidism, with imaging only when needed (MedlinePlus, updated August 2026).
| Result pattern | What it usually points to (ATA) |
|---|---|
| High TSH, low free T4 | Primary hypothyroidism (the thyroid itself is underactive) |
| Low TSH, low free T4 | A possible pituitary cause |
| Low TSH, high free T4 | Hyperthyroidism (overactive thyroid) |
- Antibodies. TPO and thyroglobulin antibody tests can help identify the cause of hypothyroidism, such as Hashimoto's thyroiditis. The ATA adds that following antibody levels over time doesn't help track response to treatment (ATA).
- Biotin. Biotin supplements can make several thyroid tests look abnormal. The ATA advises stopping biotin for 2 days before the blood draw.
Reverse T3
Reverse T3 (rT3) is a common add-on in functional medicine. The American Thyroid Association's patient guidance says an rT3 test doesn't help diagnose hypothyroidism in healthy people who are not in hospital, and isn't clinically useful (ATA, thyroid function tests). Laboratory-medicine guidance agrees:
- The Association for Diagnostics & Laboratory Medicine rates rT3 not useful for routine thyroid testing and names TSH as the main screen (ADLM).
- Alberta Precision Laboratories stopped offering the test in 2020, saying practice guidelines don't require it (Alberta Health Services).
- rT3 rises during serious illness and with some medicines, such as amiodarone, which makes results hard to interpret (ADLM).
The ATA's statement is patient guidance, not a formal clinical guideline. We didn't find an rT3 statement from the Endocrine Society.
"Optimal" ranges
Some practitioners use "optimal" thyroid ranges that are narrower than the lab's reference range. A 2012 European Thyroid Association guideline found no support for setting a target TSH different from the laboratory reference range (Wiersinga et al., Eur Thyroid J). We found no statement from the ATA, the Endocrine Society or the American Association of Clinical Endocrinology that endorses such ranges. If a practitioner uses them, ask where the range comes from and how it would change your treatment.
Treatment: levothyroxine and the alternatives
The ATA's 2014 guideline concluded that levothyroxine should remain the standard of care for hypothyroidism. It found "no consistently strong evidence" that alternatives work better for health outcomes. The alternatives it reviewed included levothyroxine plus liothyronine (T3) combinations, thyroid extract and compounded thyroid hormones (Jonklaas et al., Thyroid, 2014).
The European Thyroid Association (ETA) reached a similar view in 2012 (Wiersinga et al., Eur Thyroid J):
- Levothyroxine (L-T4) alone remains the standard treatment.
- There isn't enough evidence that adding T3 serves patients better than levothyroxine alone.
- Combination therapy may be tried as an experimental approach only in people who take levothyroxine reliably, still have symptoms despite a normal TSH, and have had other autoimmune conditions ruled out.
- It isn't recommended in pregnancy or for people with heart rhythm problems, and should be stopped if there's no improvement after 3 months.
- It should be supervised by an accredited internist or endocrinologist.
Desiccated thyroid extract
Desiccated thyroid extract is one of the alternatives the ATA's 2014 review covered. It found no consistently strong evidence that thyroid extract is better than levothyroxine for health outcomes.
The 2012 AACE and ATA hypothyroidism guideline goes further: it advises against using desiccated thyroid to treat hypothyroidism, because there is no evidence it works better than levothyroxine (Garber et al., 2012). In September 2025 the ATA said levothyroxine is the standard therapy for hypothyroidism and described FDA guidance on moving from unapproved desiccated thyroid to approved products (ATA statement, 2025).
Compounded T3
The ATA's 2014 review also included compounded thyroid hormones among the alternatives, with the same conclusion. We found no separate ATA statement on compounded T3.
Don't stop levothyroxine or change its dose without talking to the clinician who prescribes it.
Hashimoto's: selenium, iodine and gluten-free diets
| Approach | What the evidence shows | Guideline position |
|---|---|---|
| Selenium supplements | Lowered TSH slightly and lowered thyroid antibodies in people not taking thyroid hormone (2024 meta-analysis); certainty for the antibody result was low | No positive recommendation from European or American thyroid societies found |
| Iodine | Too much iodine can disrupt thyroid function in either direction (2024 narrative review) | The ATA has warned against iodine and kelp supplements above 500 micrograms a day; no ATA, ETA or British Thyroid Association guideline on iodine for Hashimoto's found |
| Gluten-free diet | A 2022 review found no evidence that a gluten-free diet helps people with Hashimoto's | No ATA or ETA recommendation found |
Selenium
A 2024 systematic review and meta-analysis of randomized trials looked at selenium in Hashimoto's thyroiditis (Huwiler et al., Thyroid, 2024). In people not taking thyroid hormone, selenium lowered TSH slightly and lowered TPO antibodies, though the certainty for the antibody result was low. It didn't change T4, T3 or thyroid size, and side effects weren't more common.
The limits matter. Trials lasted 2 to 12 months, so the effect on whether people go on to need thyroid hormone is unknown. Many trials had a high risk of bias, and the authors said the clinical meaning of the antibody drop needs more study. We found no thyroid or endocrine society guideline that recommends selenium for autoimmune thyroiditis. At a 2021 European Congress of Endocrinology debate on the question, the abstract arguing against selenium concluded that current evidence does not support routine supplementation (Endocrine Abstracts). That is one side of a debate, not a society position.
Iodine
IFM calls iodine crucial for making thyroid hormone. A 2024 narrative review notes that excess iodine can disrupt thyroid function in both directions, that observational studies link long-term high intake with autoimmune thyroiditis, and its authors advise routine supplements only during pregnancy and breastfeeding (Malinka et al., 2024). This is a review, not a guideline. In 2013 the ATA advised against iodine and kelp supplements above 500 micrograms a day (ATA statement, 2013), and we found no thyroid society guideline that recommends iodine for Hashimoto's. Ask before taking iodine supplements.
Gluten-free diets
A 2022 review in Nutrients found no evidence that a gluten-free diet is beneficial for people with Hashimoto's disease (Szczuko et al., Nutrients, 2022). The clearest link between gluten and illness is celiac disease, which is a separate diagnosis from Hashimoto's.
Questions to ask a functional medicine practitioner about thyroid care
- Do you check TSH and thyroid antibodies before making any recommendation?
- Will you work with the doctor who prescribes my thyroid medicine, and send them my results?
- Which tests beyond TSH and free T4 do you plan to order, why, and what do they cost?
- If you use "optimal" ranges, where do they come from?
- Which supplements do you suggest, what's the evidence, and do any affect thyroid medicine or thyroid tests (such as biotin)?
- Would you ever advise changing my levothyroxine? (The answer should involve the prescriber.)
When to see an endocrinologist
Ask your doctor about an endocrinologist (a hormone specialist) in these situations:
- Before trying T3 combination therapy or another alternative to levothyroxine. The ETA says combination therapy should be supervised by an accredited internist or endocrinologist.
- If symptoms continue despite a normal TSH on levothyroxine. This is the group for whom the ETA says combination therapy might be considered, only after other autoimmune conditions are ruled out and under specialist supervision.
- If tests show a low TSH with a low free T4, a pattern the ATA links to a possible pituitary cause.
- Before stopping or changing any thyroid medicine.
For new, severe or quickly worsening symptoms, see a medical doctor or urgent care first.
What to do next
- Browse functional medicine doctors and integrative medicine doctors, and check whether each one is an MD or DO who can prescribe and manage thyroid medicine.
- Read is functional medicine legit? for the overall evidence, and functional medicine cost and insurance before you sign up for a program.
- Thyroid symptoms can overlap with PCOS and perimenopause. See holistic care and medical tests for hormonal imbalance.
- Wondering what tests a naturopath can order? See can naturopathic doctors order lab tests?
Last reviewed: October 2026