Ranked by evidence
Best supplements for thyroid health
No supplement has been shown to boost a normal thyroid, and both too little and too much iodine cause thyroid disease. The few items below help only in specific situations, which is why every pick is labelled situational. If you suspect a thyroid problem, the first step is a TSH test, and confirmed hypothyroidism is treated with prescription levothyroxine.
Picks are ranked by the strength of published evidence for this goal in otherwise healthy adults. A persistent symptom needs a clinician's evaluation, and no supplement on this list replaces treatment.
Evidence last reviewed: September 2026
Situational
| Option | Evidence | Best for | The honest note | |
|---|---|---|---|---|
| Potassium Iodide | Moderate evidence | a dose-controlled iodine source | In pregnancy, iodine supplementation improves iodine status and prevents the rise in thyroglobulin. Most supplements provide 150 µg, while high doses can cause or worsen thyroid disease. | View |
| Iodine | Moderate evidence | pregnancy with low iodine intake | In pregnancy it reduced postpartum goitre, but showed no clear effect on maternal hypothyroidism or neonatal thyroid function. Check whether your salt is iodised first, and stay under the 1,100 mcg/day upper limit. | View |
| Selenomethionine | Moderate evidence | Hashimoto's thyroiditis | A meta-analysis of 35 trials found it lowered thyroid peroxidase antibodies, but free T4, T3 and thyroid volume did not change. Do not supplement if your intake is already adequate, and keep total selenium under 400 µg/day. | View |
Popular for this goal — but the evidence says skip
- Thyroid Support Formulas Limited evidence
In testing of ten products, nine contained real T3 and five contained T4, at doses that can cause thyrotoxicosis.
- Kelp (Iodine Source) Limited evidence
Iodine content varies more than 100-fold across species and harvests, and in people who were not deficient kelp tablets raised TSH within 4 weeks.
- Bladderwrack Limited evidence
No trial shows it improves thyroid function, and the documented human effects are iodine-induced thyroid problems rather than benefits.
- Sea Moss Limited evidence
No human trial supports any thyroid claim, and a single serving of gel can plausibly exceed the 1,100 mcg/day adult upper limit for iodine.
- Lugol's Iodine Solution Limited evidence
One drop supplies roughly 6 mg of iodine, far above the adult upper limit, and self-dosing is a well-documented way to trigger thyroid dysfunction.
- Guggul Limited evidence
The thyroid claim is mechanism-based marketing with no controlled human trial behind it, and guggul may interfere with thyroid medication.
Our verdict
If your iodine intake is genuinely low or you are pregnant, a standard dose of potassium iodide is the sensible choice; if you have Hashimoto's, selenomethionine lowers antibodies but does not reliably change how you feel. Skip thyroid support formulas, kelp, bladderwrack, sea moss and self-dosed Lugol's iodine.