How does DoseRank decide what ranks #1?

Each product gets a composite score blending clinical strength, evidence, dose fit, trust and value. The #1 on the DoseRank tab has the highest composite; the other tabs re-rank the same products by Value, Trust, or Popularity. Placement is never paid.

Is a higher dose always better?

No. Dose-fit rewards landing inside the range studied for the outcome — over-dosing (common with melatonin) or under-dosing both lower the score. The goal is the effective dose, not the biggest number.

What does the Value score mean?

The Value score compares a product's price per serving with clinically relevant products ranked for the same outcome. A score of 50 is the typical price; above 50 means better value than typical, while below 50 means the product costs more than typical. It is a 0–100 value signal, not a percentile.

Why is the cheapest product not #1?

Cost is only one input. The cheapest pick here is a citrate form with weaker absorption and a stock-risk flag, so it leads on Value-for-cost but trails on the composite that also weighs evidence, dose fit and availability.

Are these affiliate links?

Retailer links may be affiliate links and DoseRank may earn a commission. Rankings and placement are determined by the scoring model only — never by payment from a brand.

Is this medical advice?

No. DoseRank summarizes evidence to help you choose; it is not a substitute for a clinician, especially if you are pregnant, breastfeeding, on medication, or managing a health condition.

DOSERANKEVIDENCE-BASED SUPPLEMENTS

Improve thyroid function

DOSERANKEVIDENCE-BASED SUPPLEMENTS

Best Supplements for Thyroid function — 2263 Ranked | DOSERANK

Top decision cards

Best products for thyroid function

Ranking by · Composite outcome score

Best overall — the composite outcome score.

Top pick · DoseRank

Why this ranks #1 for thyroid function

NaturesPlus, Icelandic Kelp, 300 Tablets (150 mg per Tablet)

NaturesPlus$0.04 / serving4.9 · 9,211Available now

Also helps with

Iodine status

Why this ranks here

Evidence fitIodine leads the evidence here, backed by Kelp.
Dose fit2 of 2 dosed ingredients land in the studied range. Iodine at 150 mcg lands inside the studied 150-1000 mcg window.
Price / serving$0.04 per serving — low price tier for this outcome.
AvailabilityIn stock across major retailers; 99% availability confidence.
TrustStrong trust signals — consistently high marks from verified buyer ratings.

The numbers

150 mcgIn rangeinside the studied 150-1000 mcg window

150 mgIn rangeinside the studied 150-600 mg window

Compare top 3 Product data Open at retailer

The rest of the ranking · DoseRank

Top 10 ranked products

Oregon's Wild Harvest, Organic Kelp, 90 Organic Vegan Capsules

Oregon's Wild HarvestClinical95Dose fit81Popularity64$0.18/ serving

Oregon's Wild Harvest, Organic Kelp, 180 Organic Vegan Capsules

Oregon's Wild HarvestClinical95Dose fit81Popularity45$0.15/ serving

Nature's Way, Whole Thallus Kelp, 363 mg, 100 Capsules

Nature's WayClinical95Dose fit74Popularity30$0.11/ serving

Vitacost, Kelp, 660 mg, 180 Capsules

VitacostClinical95Dose fit81Popularity64$0.03/ serving

Life-flo, Liquid Iodine Plus with Potassium Iodide, Unflavored, 2 fl oz (59 ml)

Life-floClinical87Dose fit67Popularity99$0.02/ serving

Life Extension, Sea-Iodine™, 1,000 mcg, 60 Vegetarian Capsules

Life ExtensionClinical88Dose fit72Popularity97$0.09/ serving

NOW Foods, Potassium Plus Iodine, 180 Tablets

NOW FoodsClinical87Dose fit69Popularity90$0.05/ serving

21st Century, One Daily, Men's Health, 100 Tablets

21st CenturyClinical87Dose fit67Popularity99$0.07/ serving

21st Century, One Daily, Women's, 100 Tablets

21st CenturyClinical87Dose fit67Popularity98$0.07/ serving

Top decision cards

Best products for thyroid function

Ranking by · Composite outcome score

Best overall — the composite outcome score.

Top pick · DoseRank

Why this ranks #1 for thyroid function

NaturesPlus, Icelandic Kelp, 300 Tablets (150 mg per Tablet)

NaturesPlus$0.04 / serving4.9 · 9,211Available now

Also helps with

Iodine status

Why this ranks here

Evidence fitIodine leads the evidence here, backed by Kelp.
Dose fit2 of 2 dosed ingredients land in the studied range. Iodine at 150 mcg lands inside the studied 150-1000 mcg window.
Price / serving$0.04 per serving — low price tier for this outcome.
AvailabilityIn stock across major retailers; 99% availability confidence.
TrustStrong trust signals — consistently high marks from verified buyer ratings.

The numbers

150 mcgIn rangeinside the studied 150-1000 mcg window

150 mgIn rangeinside the studied 150-600 mg window

Compare top 3 Product data Open at retailer

The rest of the ranking · DoseRank

Top 10 ranked products

Oregon's Wild Harvest, Organic Kelp, 90 Organic Vegan Capsules

Oregon's Wild HarvestClinical95Dose fit81Popularity64$0.18/ serving

Oregon's Wild Harvest, Organic Kelp, 180 Organic Vegan Capsules

Oregon's Wild HarvestClinical95Dose fit81Popularity45$0.15/ serving

Nature's Way, Whole Thallus Kelp, 363 mg, 100 Capsules

Nature's WayClinical95Dose fit74Popularity30$0.11/ serving

Vitacost, Kelp, 660 mg, 180 Capsules

VitacostClinical95Dose fit81Popularity64$0.03/ serving

Life-flo, Liquid Iodine Plus with Potassium Iodide, Unflavored, 2 fl oz (59 ml)

Life-floClinical87Dose fit67Popularity99$0.02/ serving

Life Extension, Sea-Iodine™, 1,000 mcg, 60 Vegetarian Capsules

Life ExtensionClinical88Dose fit72Popularity97$0.09/ serving

NOW Foods, Potassium Plus Iodine, 180 Tablets

NOW FoodsClinical87Dose fit69Popularity90$0.05/ serving

21st Century, One Daily, Men's Health, 100 Tablets

21st CenturyClinical87Dose fit67Popularity99$0.07/ serving

21st Century, One Daily, Women's, 100 Tablets

21st CenturyClinical87Dose fit67Popularity98$0.07/ serving

Improve thyroid function

Improve thyroid function

Which ingredient types matter for thyroid functionOpen to see which ingredient types matter for thyroid function

Glandulars & Animal-Derived Extracts

Minerals & Trace Elements

Botanicals/Herbal Extracts

Best products for thyroid function

NaturesPlus, Icelandic Kelp, 300 Tablets (150 mg per Tablet)

Oregon's Wild Harvest, Organic Kelp, 90 Organic Vegan Capsules

Oregon's Wild Harvest, Organic Kelp, 180 Organic Vegan Capsules

Nature's Way, Whole Thallus Kelp, 363 mg, 100 Capsules

Vitacost, Kelp, 660 mg, 180 Capsules

Life-flo, Liquid Iodine Plus with Potassium Iodide, Unflavored, 2 fl oz (59 ml)

Life Extension, Sea-Iodine™, 1,000 mcg, 60 Vegetarian Capsules

NOW Foods, Potassium Plus Iodine, 180 Tablets

21st Century, One Daily, Men's Health, 100 Tablets

21st Century, One Daily, Women's, 100 Tablets

What every metric means

Compare the top 3, side by side

Not sure which is right for you?

Get a personal report

Frequently asked

Which ingredient types matter for thyroid functionOpen to see which ingredient types matter for thyroid function

Glandulars & Animal-Derived Extracts

Minerals & Trace Elements

Botanicals/Herbal Extracts

Compare the top 3, side by side

Best products for thyroid function

NaturesPlus, Icelandic Kelp, 300 Tablets (150 mg per Tablet)

Oregon's Wild Harvest, Organic Kelp, 90 Organic Vegan Capsules

Oregon's Wild Harvest, Organic Kelp, 180 Organic Vegan Capsules

Nature's Way, Whole Thallus Kelp, 363 mg, 100 Capsules

Vitacost, Kelp, 660 mg, 180 Capsules

Life-flo, Liquid Iodine Plus with Potassium Iodide, Unflavored, 2 fl oz (59 ml)

Life Extension, Sea-Iodine™, 1,000 mcg, 60 Vegetarian Capsules

NOW Foods, Potassium Plus Iodine, 180 Tablets

21st Century, One Daily, Men's Health, 100 Tablets

21st Century, One Daily, Women's, 100 Tablets

Improve thyroid function

Improve thyroid function

Which ingredient types matter for thyroid functionOpen to see which ingredient types matter for thyroid function

Glandulars & Animal-Derived Extracts

Minerals & Trace Elements

Botanicals/Herbal Extracts

Best products for thyroid function

NaturesPlus, Icelandic Kelp, 300 Tablets (150 mg per Tablet)

Oregon's Wild Harvest, Organic Kelp, 90 Organic Vegan Capsules

Oregon's Wild Harvest, Organic Kelp, 180 Organic Vegan Capsules

Nature's Way, Whole Thallus Kelp, 363 mg, 100 Capsules

Vitacost, Kelp, 660 mg, 180 Capsules

Life-flo, Liquid Iodine Plus with Potassium Iodide, Unflavored, 2 fl oz (59 ml)

Life Extension, Sea-Iodine™, 1,000 mcg, 60 Vegetarian Capsules

NOW Foods, Potassium Plus Iodine, 180 Tablets

21st Century, One Daily, Men's Health, 100 Tablets

21st Century, One Daily, Women's, 100 Tablets

What every metric means

Compare the top 3, side by side

Not sure which is right for you?

Get a personal report

Frequently asked

Related outcomes

Related outcomes

Which ingredient types matter for thyroid functionOpen to see which ingredient types matter for thyroid function

Glandulars & Animal-Derived Extracts

Minerals & Trace Elements

Botanicals/Herbal Extracts

Compare the top 3, side by side

Best products for thyroid function

NaturesPlus, Icelandic Kelp, 300 Tablets (150 mg per Tablet)

Oregon's Wild Harvest, Organic Kelp, 90 Organic Vegan Capsules

Oregon's Wild Harvest, Organic Kelp, 180 Organic Vegan Capsules

Nature's Way, Whole Thallus Kelp, 363 mg, 100 Capsules

Vitacost, Kelp, 660 mg, 180 Capsules

Life-flo, Liquid Iodine Plus with Potassium Iodide, Unflavored, 2 fl oz (59 ml)

Life Extension, Sea-Iodine™, 1,000 mcg, 60 Vegetarian Capsules

NOW Foods, Potassium Plus Iodine, 180 Tablets

21st Century, One Daily, Men's Health, 100 Tablets

21st Century, One Daily, Women's, 100 Tablets