Herbs & Spices · Herbs

Bladderwrack: Benefits for Thyroid & Gut, Dosage and Safety

Q: Is bladderwrack the same as kelp?

No, though the names overlap: bladderwrack is a Fucus seaweed, a wrack, while sugar kelp and its relatives in the kelp family, Laminariaceae, carried the most iodine of the seaweeds tested in Greenland.[14] In Danish samples, sugar kelp averaged about 2,300 mcg of iodine per gram, against about 275 for bladderwrack.[2] Nineteenth-century writers used the word kelp for the ash of burned seaweeds such as bladderwrack.[11]

What bladderwrack is, how its whole-food iodine and fiber work on the thyroid and the gut, what the research shows, how much to take and how to use the powder, tea and capsules.

By Dr. Josh Axe, DC, DNM, CNS·Medically reviewed by the DrAxe.com Medical Advisory Board·22-min read

Meet the Medical Advisory Board

Evidence-based42 sources citedUpdated October 23, 2026

Published Oct 23, 2026Last updated Oct 23, 2026Editorial policyMedical review policyFact-checking policy

The Dr. Axe Score™

6.1/10

Overall Dr. Axe Score · Bladderwrack

Bladderwrack scores 6.1 for some five centuries of recorded thyroid use, from 16th-century China to the British Herbal Pharmacopoeia and an EU traditional-use registration, for measured whole-food iodine, for its place among the sea vegetables in my Hypothyroidism Protocol, and for first human trials on HDL cholesterol, blood sugar and the gut.

Scientific Evidence

4.8/10

A 12-week placebo-controlled trial of bladderwrack alone raised HDL; placebo-controlled trials of blends with its cousin knotted wrack improved insulin and HbA1c; its iodine is well measured; single doses and a 5-week trial of the whole seaweed didn't change blood sugar.

Traditional Medicine

7.8/10

Roman, Chinese, French and British use; the Eclectic physicians; the British Herbal Pharmacopoeia (1983); an EU traditional-use registration.

Clinical Effectiveness

6.2/10

Sea vegetables are #3 among the thyroid foods in my Hypothyroidism Protocol, in gentle amounts, and bladderwrack's iodine is absorbed and reaches the thyroid.

Safety

5.9/10

No known side effects at the EU traditional dose; deductions for thyroid upsets from too much iodine, iodine that varies by batch, stomach upset at 5 grams a day, a kidney case report and product contamination.

Why this score?

Why Bladderwrack scores 6.1 / 10

A trial of bladderwrack itself for a thyroid outcome would raise it. Weighting: Evidence 30% · Traditional Medicine 25% · Clinical Effectiveness 25% · Safety 20% (4.8×0.30 + 7.8×0.25 + 6.2×0.25 + 5.9×0.20 = 1.44 + 1.95 + 1.55 + 1.18 = 6.12, shown as 6.1). Interactions are rated separately and don't change the score. How we score

A transparent, weighted index built for supplements. See how it’s calculated →

Interaction check: Moderate. Bladderwrack's iodine is what makes it work, and it's also why it can add to medicines that act on the thyroid.9

Thyroid medicines and iodine products, such as levothyroxine or the antithyroid drug methimazole: the EU monograph says not to combine bladderwrack with thyroid medicines or other iodine products, and in one report, bladderwrack added to a selenium supplement made radioactive iodine treatment fail.9 34 Keep taking your medicine as prescribed, and ask the doctor who manages your thyroid before adding bladderwrack.

Lithium: a man taking lithium developed an overactive thyroid while taking bladderwrack, and it settled after he stopped.35 Skip bladderwrack supplements while you take lithium unless your prescriber agrees.

Amiodarone, an iodine-rich heart-rhythm drug: people taking it are among those whose thyroid may not adjust to extra iodine.36 Skip bladderwrack supplements while you take it.

Blood thinners, such as warfarin: in a single-blind trial against a placebo group, 3 grams a day of fucoidan from a related seaweed for 12 days lengthened one clotting test within the normal range in 10 adults, and the researchers saw no clear blood-thinning effect from taking it by mouth.37 Tell the doctor who manages your blood thinner before adding bladderwrack supplements.

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Bladderwrack at a glance

Bladderwrack is a brown seaweed of North Atlantic shores, used for centuries to support the thyroid, and it brings two things your body uses: whole-food iodine, the raw material for thyroid hormone, and fiber that feeds your gut.1 2 3

What it does: supplies iodine for the thyroid, feeds gut bacteria, and in trials raised HDL cholesterol, with blends led by its cousin knotted wrack improving insulin and HbA1c4 5 6 7
How much: gentle amounts as a food, since half a gram of the dried seaweed carries about an adult's daily iodine, or the EU's traditional 130 mg of powder twice a day2 8 9
How to use it: flaked or powdered in food, as capsules of the dried powder, or as a tea or tincture1 9
With Hashimoto's or another thyroid condition, get your iodine from food and skip bladderwrack supplements unless your doctor has tested you and advised it, and skip them in pregnancy and while nursing10 9

Bladderwrack, also written bladder wrack, is a brown seaweed that grows on the rocky shores of Europe and North America, named for the air-filled bladders set in pairs along its fronds.11 It carries iodine, the mineral your thyroid makes its hormones from, in a seaweed that's about half fiber, so it feeds your thyroid and your gut at the same time.2 3 The bladders run from the size of a pea to a hazelnut, on an olive-green frond that dries almost black.11

People used it for the thyroid long before anyone knew what iodine was. It was used for goiter in China from the 16th century and in France from the 17th, and British herbalists still listed it for an underactive thyroid in 1983.1 Those healers were feeding the gland. A sluggish thyroid is a signal that something upstream is short or off, and as I wrote in my Hypothyroidism Protocol, your thyroid can't build or activate hormone without raw materials.12

On my show, I've named bladderwrack alongside kelp as a seaweed source of iodine, and sea vegetables rank third among the top 10 thyroid foods in my protocol, in gentle amounts.13 12

Seaweed's high-fiber content promotes digestion, it fights free radicals, it lowers cholesterol, and because it contains healthy quantities of iodine, it supports thyroid health.Dr. Josh Axe, DC, DNM, CNSFrom Ancient Remedies (2021), p. 101

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Did you know?

Bladderwrack's air bladders grow in pairs along the frond, each from the size of a pea to the size of a hazelnut.11
In the 19th century, bladderwrack was burned in a covered crucible to make a charcoal called vegetable ethiops, given for swollen glands because of the iodine it held.11
Capsules of powdered bladderwrack have been sold in France since 1981 as a traditional aid to slimming diets.1

What is bladderwrack?

Quick answer

Bladderwrack is Fucus vesiculosus, a brown seaweed of the rocky shores of Europe and North America, known in older texts as bladder-wrack, sea-wrack, cut-weed, kelp-ware and black-tang.11 It's used dried, as a food, a powder, a tea, a tincture and capsules.1

The frond runs from a few inches to 4 feet long, flat, with a midrib down its length, forking again and again, with its air bladders in pairs.11 Like wakame and the kelps, it's a brown seaweed.14 15

Dried bladderwrack is a dense package. In 27 Danish samples, it averaged about 275 mcg of iodine per gram, with a range of 138 to 451, and most of that iodine is bound in organic compounds.2 1 Tested Fucus products were 45% to 59% dietary fiber.3 Its polyphenols make up about 15% of the plant, mostly phlorotannins, and it carries potassium, calcium, magnesium and iron.1 14

Iodine

About 275 mcg per gram, dried

The mineral your thyroid builds T4 and T3 from, joined to the amino acid tyrosine.2 4

Fucoidan and alginate

Fiber, 45% to 59% of dried products

Fucoidan is a sulfated fiber built mainly from a sugar called L-fucose, and alginic acid makes up about 12% of the plant.1 3

Phlorotannins

About 15% polyphenols

Brown-seaweed polyphenols and the main antioxidants in bladderwrack powder; gut bacteria ferment them in lab tests.1 3 5

Dried flakes or powder

The whole dried seaweed, the form used in food and in the human trial of the whole plant.16

Capsules

Powdered seaweed, the form behind the EU's traditional dose of 130 mg twice a day.9

Tea

An infusion of the dried seaweed, listed in the British Herbal Pharmacopoeia and sold in herbal-tea blends in Poland since 1989.1

Tincture

An alcohol extract; the British Herbal Compendium listed 4 to 10 mL a day of a 1:5 tincture.1

A short history of bladderwrack

The Romans knew bladderwrack and used it for joint complaints. From the 16th century, it was used in China for goiter caused by iodine deficiency, and in 17th-century France for goiter and other thyroid complaints. British practice added it for corpulence, and American practice for psoriasis and as a strengthening agent.1

The Eclectic physicians, the 19th-century American practitioners who built their practice on plants, recorded iodine in its ash and the use of its charcoal for swollen glands.11 They also recorded its use to lessen obesity, and used it to ease kidney congestion and bladder irritation and for menstrual problems.11

The British Herbal Pharmacopoeia of 1983 listed it for myxedema, the old name for a severely underactive thyroid, and for goiter, obesity and rheumatism, with obesity tied to an underactive thyroid as its specific use.1 The British Herbal Compendium of 1992 called it thyroactive.1 Today, the European Union registers it as a traditional herbal medicine, with products on European markets since 1968.9 1

What is bladderwrack good for?

Quick answer

Bladderwrack is a brown seaweed used for centuries to support the thyroid and digestion: it brings whole-food iodine, the raw material your thyroid makes its hormones from, and its fiber feeds the gut, and my Hypothyroidism Protocol ranks a leaky gut as the number one driver of low thyroid.1 4 3 12 In people, a 12-week placebo-controlled trial of bladderwrack raised HDL cholesterol from about 49 to 52 mg/dL, and placebo-controlled trials of blends led by its cousin knotted wrack improved insulin and HbA1c.6 17 7

Where the research stands

Bladderwrack's thyroid and digestive uses rest on a long recorded tradition and on measured iodine and fiber. Bladderwrack on its own has been tested in five controlled trials in people, from a single dose to 12 weeks, plus a case report and a skin study; the blood sugar and inflammation results come mainly from blends with its cousin knotted wrack, each labeled in the rows below.6 18 19 16 20 21 22

Bladderwrack benefits, graded by evidence (updated October 2026). Evidence labels are editorial judgments that compare these uses with each other; they aren't formal certainty ratings.
Use	Evidence	Product studied	What the research shows
Thyroid (iodine)	Traditional	Whole seaweed; knotted wrack capsules	A goiter remedy for centuries; urinary iodine rose from 78 to 140 mcg/L on half a gram a day of knotted wrack1 23
Gut health	Emerging	Fucoidan from bladderwrack and wakame; bladderwrack compounds	A gut-lining defense protein rose 45% in a week; gut bacteria made butyrate from its compounds15 5 24
Blood sugar	Emerging	Blends with knotted wrack, one with chromium	Insulin 12.1% lower after a meal; HbA1c from 7.4% to 6.6% in 6 months17 7
HDL cholesterol	Emerging	Bladderwrack extract, 2,000 mg a day	HDL up from about 49 to 52 mg/dL in 12 weeks, against a dip on placebo6
Weight	Traditional	Powdered bladderwrack; brown seaweeds	A registered traditional aid to a reduced-calorie diet; lower BMI in pooled trials9 25
Inflammation	Emerging	Blend with knotted wrack	IL-6 rose 15% against 57% on placebo over 12 weeks26
Joints	Mixed	Extract 85% bladderwrack with B6, zinc and manganese; bladderwrack fucoidan extract	Symptom score down 52% at 1,000 mg; no difference from placebo at 300 mg27 20
Women's cycles	Traditional	Dried bladderwrack powder	Longer cycles in all three women; lower estrogen and higher progesterone in one11 21
Skin	Emerging	1% bladderwrack extract gel	More elastic cheek skin than the control side22

How bladderwrack works in your body

Fatigue, weight that won't move and cold hands are signals, and two of the upstream drivers behind a slow thyroid are missing raw materials and a gut that's out of balance.12 Most patients I see have several of these drivers running at once, which is why my Thyroid Reset works on all of them, in order.12 Bladderwrack touches both. Here's what happens, step by step:

1Iodine from the sea

Bladderwrack draws iodine out of seawater and stores it, about 275 mcg per gram of the dried seaweed.2

2Into your thyroid

Your thyroid pulls iodine from the blood and joins it to tyrosine to build T4 and T3.4 Iodine from seaweed is absorbed and shows up in the urine, the standard way to measure iodine status.23 28

3Fiber reaches your gut

About half of dried bladderwrack is fiber, including alginate and fucoidan, and much of it travels on to the colon, where gut bacteria live.3 1 5

4Gut bacteria make butyrate

In lab tests with human gut bacteria, its fiber and phlorotannins were fermented into butyrate and propionate, and butyrate makers such as Faecalibacterium grew.5 24

5The gut lining answers

Lysozyme, a defense protein made by cells of the gut lining, rose after a week of fucoidan from bladderwrack and wakame in a pilot of 22 athletes with no placebo group.15 That lining is the focus of the gut step in my Thyroid Reset.12

Its iodine is the thyroid's raw material, its fiber works on the gut, and its polyphenols slowed the enzymes that break starch into sugar in lab tests, one reason researchers have measured blood sugar and insulin after meals in people taking it.1 17 On my show, I've said that your body has an incredible capacity to heal, and that your thyroid, adrenals and gut are all connected, so the job is to give the thyroid the nutrients it needs, clear out the toxins and put it in an environment that can heal.29 Bladderwrack gives you the iodine part of that job, in food form.

Bladderwrack benefits

Bladderwrack's benefits start with the thyroid and the gut and reach out to blood sugar, cholesterol, weight, inflammation, the joints and the skin:

Thyroid support: whole-food iodine

Traditional useTraditional useTraditional use · Chinese, French and British records; human study of a cousin seaweed, 42 women, no comparison group

Bladderwrack feeds the thyroid its raw material, iodine, and it was a goiter remedy for centuries in China, in France and in British herbal practice.1 In a study of 42 women with no comparison group, half a gram a day of its close cousin knotted wrack nearly doubled urinary iodine in 2 weeks.23 The thyroid section has the details and a chart.

Study takeaway: a centuries-old goiter remedy that supplies the thyroid's raw material.

Feeds a healthy gut

Emerging evidenceHuman studyPilot study · 22 athletes, no placebo group; lab studies with human gut bacteria

About half of dried bladderwrack is fiber, and human gut bacteria ferment it into butyrate in lab tests.3 5 24 In a pilot study of 22 professional athletes with no placebo group, a week of fucoidan from bladderwrack and wakame raised lysozyme, a defense protein made by the gut lining, by about 45%.15 See the gut section.

Study takeaway: fiber that gut bacteria turn into butyrate, and a stronger gut-lining signal in a week.

Blood sugar support

Emerging evidenceHuman studyPlacebo-controlled trials of blends with knotted wrack · 23 adults who each tried both; 175 adults with type 2 diabetes, 164 finished

Bladderwrack blends help your body handle a starchy meal with less insulin: after a single 500 mg dose of a blend of bladderwrack and its cousin knotted wrack, insulin after a bread meal ran 12.1% lower and insulin sensitivity 7.9% higher than after a placebo, in 23 adults who each tried both, in a trial where neither the people nor the researchers knew who got what.17 Their glucose response didn't differ.17

In a 6-month trial, 175 adults with type 2 diabetes on their usual medicines took an extract that was 95% knotted wrack and 5% bladderwrack, with chromium, or a placebo; among the 164 who finished, HbA1c fell from 7.4% to 6.6% on the extract and from 7.2% to 7.0% on placebo, and fasting glucose dropped from 152.4 to 116.8 mg/dL.7 In 65 adults with prediabetes, the same blend brought 18.2% back to normal blood sugar, against none on placebo.30 In placebo-controlled trials of bladderwrack alone, single doses of its extract and 5 grams a day of the dried whole seaweed for 5 weeks didn't change blood sugar.18 19 16 Our guide to normal blood sugar covers the daily habits that steady it.

Study takeaway: blends with knotted wrack lowered insulin after meals and HbA1c over 6 months.

HbA1c over 6 months on a knotted wrack and bladderwrack extract

Source: Derosa et al. · Diabetes, Metabolic Syndrome and Obesity, 2019 [7]Average HbA1c at the start and after 6 months. Lower is better.

Healthier HDL cholesterol

Emerging evidenceHuman studyPlacebo-controlled trial · 34 overweight adults, 12 weeks

Bladderwrack on its own raised HDL, the protective cholesterol, in 12 weeks: in 34 overweight adults with LDL above 77 mg/dL (2.0 mmol/L), 2,000 mg a day of a polyphenol-rich bladderwrack extract took HDL from about 49 to 52 mg/dL (1.28 to 1.35 mmol/L), while it went from about 53 to 52 on placebo; neither the people nor the researchers knew who got what, and the other blood markers didn't change.6 Across 11 randomized trials in adults with overweight or obesity, seaweed lowered total cholesterol by 7.72 mg/dL and LDL by 7.33 mg/dL.25 Our guide to HDL cholesterol covers the food side.

Study takeaway: HDL up in 12 weeks on bladderwrack alone, against a dip on placebo.

Weight-loss support

Traditional useTraditional useEU traditional-use registration · pooled analysis of 11 randomized trials of seaweed; mice

Bladderwrack is registered in the EU as a traditional aid to a reduced-calorie diet for overweight adults, at 130 mg of the powder twice a day.9 The use goes back to the 19th century, when Duchesne-Duparc recommended an infusion or pills of it to lessen obesity, an effect King's American Dispensatory says took 3 or 4 weeks of use to show.11

Across 11 randomized trials, seaweed lowered BMI and body fat in adults with overweight or obesity, with the effect seen when refined or extracted brown seaweed was taken for 8 weeks or longer.25 In one 12-week placebo-controlled trial, a blend with knotted wrack added no weight loss to diet advice alone.26 In mice on a high-fat diet, L-fucose, the sugar fucoidan is mainly built from, cut weight gain and liver fat over 10 weeks.31 1

Study takeaway: a registered traditional aid to a lighter diet, with pooled trial support for brown seaweed.

Calmer inflammation

Emerging evidenceHuman studyPlacebo-controlled trial of a blend · 56 adults, 12 weeks; study of 10 adults, no comparison group

Bladderwrack blends held back the rise in inflammation: in 56 adults with prediabetes and overweight who finished a 12-week placebo-controlled trial, IL-6, an inflammatory messenger, rose 15% on 500 mg a day of a blend with knotted wrack, against 57% on placebo.26 In the prediabetes trial above, hs-CRP and TNF-α fell on the blend with chromium.30 In 10 adults taking an extract that was 85% bladderwrack for 4 weeks, with no comparison group, IL-6 went down.32 For everyday support, see these anti-inflammatory foods.

Study takeaway: a smaller rise in IL-6 than placebo over 12 weeks.

Joint comfort

Mixed evidenceHuman studyStudy of 12 adults with knee osteoarthritis, people knew which dose they got · placebo-controlled trial, 122 adults, 96 finished

The Romans used bladderwrack for joint complaints, and Western herbalists rubbed it on sore knees as a liniment.1 27 In 12 adults with knee osteoarthritis who knew which dose they got, an extract that was 85% bladderwrack, with vitamin B6, zinc and manganese, cut their arthritis symptom score by 52% at 1,000 mg a day and 18% at 100 mg over 12 weeks.27 In a placebo-controlled trial of 300 mg a day of a bladderwrack fucoidan extract, symptoms in the 96 people who finished improved about as much as on placebo.20 Our guide to natural remedies for joint pain covers the other natural options to pair with it.

Study takeaway: a 52% lower symptom score at 1,000 mg a day in a first study.

More elastic skin

Emerging evidenceHuman studyHuman skin study · 1% extract gel, 5 weeks, compared with a control

On the skin, bladderwrack improves elasticity: a gel with 1% bladderwrack extract, applied to the cheek twice a day for 5 weeks, made the skin thinner and more elastic than the control, the opposite of the thickening and stiffening that come with age.22 It also has a traditional use on wounds, and burns are among the skin conditions it has been used for.1

Study takeaway: more elastic cheek skin in 5 weeks.

Bladderwrack for the thyroid: whole-food iodine

Quick answer

Bladderwrack supports the thyroid by supplying iodine, the mineral your thyroid joins to tyrosine to make T4 and T3, and it was a goiter remedy in China from the 16th century and in France from the 17th.4 1 Dried bladderwrack averaged about 275 mcg of iodine per gram in 27 Danish samples, so a gentle amount covers a day's need.2 8

Over the years, I've sat across from thousands of people, most of them women, carrying the same story: bone-deep fatigue, weight that won't move no matter how little they eat, cold hands, thinning hair, brain fog, low mood, and a lab report that says everything is normal.12 Iodine is one of the raw materials to look at first. In an iodine deficiency, the gland can't make enough hormone, and it can swell into a goiter.28

Every food is information for your thyroid, and sea vegetables deliver whole-food iodine and tyrosine, the building blocks of the hormone.12 Bladderwrack's record here is long, and I give it real weight: people on two continents relied on bladderwrack for goiter and the thyroid for some five centuries, long before anyone could measure the iodine in it.1 11

The modern measurements explain it. At about 275 mcg of iodine per gram, half a gram of dried bladderwrack carries roughly an adult's daily 150 mcg.2 8 And seaweed iodine gets where it's needed. In a 2-week study of 42 British women of childbearing age who ate little dairy or seafood, half a gram a day of whole knotted wrack, bladderwrack's close cousin, raised their median urinary iodine from 78 to 140 mcg/L, with no comparison group.23 Their TSH rose from 1.5 to 2.1 mIU/L, with two women above the normal range and free T4 normal in all.23 In the absorption test, 22 women took up about 33% of the seaweed's iodine, against 59% from a potassium iodide pill.23

Half a gram of knotted wrack a day: urinary iodine up from 78 to 140

Source: Combet et al. · British Journal of Nutrition, 2014 [23]Median urinary iodine before and after 2 weeks of half a gram of seaweed a day.

Iodine works with partners. Selenium runs the enzymes that turn T4 into active T3, and my protocol supplies it with one to two Brazil nuts a day.12 My rule for iodine itself is to get it from food, from sea vegetables, wild fish and eggs: enough, not mega.12 A pinch of dried bladderwrack in a pot of soup or a seasoning blend fits that rule well, and our guide to iodine-rich foods has the other sources, ranked.

Four thyroid markers worth knowing

These tests show how your thyroid is working and whether autoimmunity is part of the picture, and no single result diagnoses a thyroid condition on its own.

TSH: The pituitary's signal to your thyroid. It rises when the thyroid is underactive.
Free T4: The main hormone your thyroid releases, the raw material for T3.
Free T3: The active thyroid hormone, made mostly by selenium-dependent enzymes.
TPO antibodies: The antibodies that mark autoimmune (Hashimoto's) thyroiditis.

See the cellular bloodwork panel

Have results? Analyze them free →

Bladderwrack for gut health

Quick answer

Bladderwrack feeds your gut with fiber, 45% to 59% of the dried seaweed, and in lab tests human gut bacteria fermented its compounds into butyrate and propionate.3 5 24 In 22 professional athletes, a week of fucoidan from bladderwrack and wakame raised lysozyme, a defense protein made by the gut lining, by about 45%, in a pilot with no placebo group.15

The gut sits at the center of thyroid health. In my Hypothyroidism Protocol, a leaky gut is the number one driver of low thyroid: a permeable gut lets food and microbial particles into the blood, the immune system that lives in your gut turns on, and sealing the gut calms that attack.12

In working with thousands of patients with hypothyroidism, I found that almost all of them have a microbial imbalance in the gut: too much bad bacteria, not enough good.Dr. Josh Axe, DC, DNM, CNSFrom How to Heal Hypothyroidism and Hashimoto's Naturally, The Dr. Josh Axe Show (2024), at 21:53

Bladderwrack has a long digestive record. Its reported traditional uses include an irritated stomach, heartburn, reflux, constipation and colitis, and herbal-tea blends with it have been sold in Poland since 1989 for short-term constipation.1 Its alginic acid is a soluble fiber.33

That fiber feeds the bacteria in your colon. When researchers ran bladderwrack's phlorotannins through a simulated digestion and then fermented them with human stool, propionate and butyrate rose.5 A bladderwrack fiber fermented the same way raised butyrate and other short-chain fatty acids and favored butyrate makers such as Faecalibacterium, while Shigella fell.24 Fibers like these act as prebiotics, food for the bacteria in your gut.

The first human signal comes from the gut lining. Lysozyme is a defense protein released by Paneth cells, specialized cells deep in the lining of the small intestine.15 In 22 male professional athletes at a week-long training camp, 1 gram a day of fucoidan from bladderwrack and wakame for 7 days raised lysozyme in their stool from 387.5 to 562.9 ng/mL, about 45%, toward the healthy adults' level of 670.8, and it rose in 74% of the athletes.15 That was a pilot with no placebo group, funded by the fucoidan's supplier.15

A week of bladderwrack and wakame fucoidan: gut-lining lysozyme up about 45%

Source: Cox et al. · Marine Drugs, 2020 [15]Average lysozyme, a defense protein made by gut-lining cells, before and after a week of fucoidan.

Sealing the gut lining is step two of my Thyroid Reset, built on foods like bone broth, cooked greens, wild fish and pasture-raised eggs.12 Sea vegetables join them in step three, Nourish, in gentle amounts.12

Bladderwrack benefits for women: cycle and hormone balance

Quick answer

Bladderwrack may help lengthen short or irregular cycles: in a case report of three women, 700 mg to 1.4 grams a day of dried bladderwrack lengthened every woman's cycle, and in the one woman tested, estrogen fell and progesterone rose.21 The Eclectic physicians of the 1890s recommended it for menstrual problems.11

Bladderwrack's place in women's health is old. King's American Dispensatory, the Eclectic reference of 1898, recommended it for "menstrual derangements."11 A century later, a researcher gave bladderwrack to three women aged 21 to 43 with abnormal cycles. All three had heavy, painful periods, and two had endometriosis.21 They took dried, powdered bladderwrack in capsules, 700 mg a day and then, for two of them, 1.4 grams.21

Every woman's cycle lengthened. The woman with the shortest cycles went from about 16 days to 26 on the lower amount and 31 on the higher one, and she began ovulating again.21 The other two went from 23 to 28.5 days and from 27 to 36 days, and all three bled for fewer days.21 The two women with endometriosis reported much less pain during their periods and through the cycle.21

In the woman whose hormones were tracked, estradiol fell from 626 to 164 pg/mL on 700 mg a day and to 92.5 on 1.4 grams, and progesterone rose from 0.58 to 8.4 and then 16.8 ng/mL.21 A three-woman case report is a small start, and it lines up with the tradition. Our guides to irregular periods and female hormones cover the food and lifestyle steps that support a steady cycle.

How to use bladderwrack: forms and dosage

Quick answer

The EU's traditional dose, registered for weight management, is 130 mg of powdered bladderwrack twice a day, with a glass of water, 2 hours before meals, keeping total iodine from bladderwrack products under 400 mcg a day.9 As a food, use gentle amounts: half a gram of the dried seaweed carries roughly an adult's daily 150 mcg of iodine.2 8

Bladderwrack's dose is really an iodine dose, so think in micrograms. Adults need 150 mcg of iodine a day, 220 in pregnancy and 290 while nursing, and the upper limit from all sources is 1,100.8

As a food: a pinch of the dried, flaked or powdered seaweed in soups, broths or seasoning blends. Half a gram carries about 140 mcg at the Danish average, and the range runs from about 70 to 225 mcg.2
Capsules: 130 mg of powdered bladderwrack twice a day, the EU's traditional dose for adults, taken with water 2 hours before meals.9
Older herbal amounts: the British Herbal Compendium of 1992 listed 0.8 to 2 grams a day of the dried seaweed, or 4 to 10 mL a day of a 1:5 tincture.1 At the Danish average, 0.8 to 2 grams carries roughly 220 to 550 mcg of iodine, so the lower end suits a gentle approach.2
Pair it with: one to two Brazil nuts a day for selenium, plus wild fish and eggs, the other iodine foods on my list.12

Pharmacopoeia-grade bladderwrack powder carries 0.03% to 0.2% iodine, 300 to 2,000 mcg per gram, which is why the EU asks makers to blend batches so the traditional dose stays under 400 mcg of iodine a day.9 And iodine is only one raw material. I have watched patients optimize every nutrient and still stall until they addressed the stress and story driving the disease.12 That's why my Hypothyroidism Protocol also calms cortisol, with ashwagandha, an adaptogen, and daily practices for stress.12

Want help fitting bladderwrack into your routine?

Ask Dr. Axe AI. Answers are grounded in this library, with sources shown.

How to choose bladderwrack

Seaweed takes up minerals from the water it grows in, metals included, so where it was harvested matters.14

Clean water: the label or the seller should name where it was harvested.14
Tested for metals: ask for a test for arsenic, lead, cadmium and mercury.
Iodine on the label: a product should state its iodine per serving, since it varies from batch to batch.2 9

Bladderwrack side effects and who should skip it

Hashimoto's and other thyroid conditions. In my Hashimoto's Protocol, my answer to "Can I take iodine?" is to get iodine from food and avoid kelp and high-dose iodine unless your doctor has tested you and advised it, because too much can worsen autoimmunity.10 Bladderwrack supplements belong in that group: in a placebo-controlled trial of 36 healthy adults, 4 weeks of kelp capsules raised TSH, and case reports describe overactive and underactive thyroids after kelp tea, tablets and kelp-based diets.38 39 40 41 Have TSH, free T4 and thyroid antibodies tested first, so the numbers guide the decision.

Pregnancy, breastfeeding and children. Skip bladderwrack supplements in pregnancy and while nursing: their safety hasn't been established, and iodine and heavy metals both pass into breast milk.9 33 Get your iodine from wild fish, eggs and small amounts of sea vegetables, toward the 220 mcg a day you need in pregnancy and 290 while nursing.8 The EU monograph doesn't recommend it for anyone under 18.9

Kidney disease. Skip it: kidney injury has been reported with bladderwrack, including a disorder of the kidney's tubules called Fanconi syndrome.42 1

Heavy metals. Most of the arsenic in seaweed is stored as arsenosugars, which are considered less toxic than inorganic arsenic.14 One tested batch of dried bladderwrack carried 0.21 mg/kg of inorganic arsenic, and no Greenland sample of 10 seaweed species exceeded EU limits for cadmium, mercury or lead.16 14 Buy bladderwrack that names its harvest waters and comes with a metals test; our guide to arsenic poisoning covers the signs.

At normal amounts. The EU monograph lists no known side effects at its traditional dose.9 At 5 grams a day of the dried seaweed, three people in one trial's bladderwrack group stopped because of stomach and gut complaints, so start with small amounts.16 Stop if you notice a racing or pounding heart, trembling or an acne flare, the signs of too much listed in the EU monograph, or a rash or swelling after taking it.9

The bottom line

Is bladderwrack worth taking?

Yes, in gentle amounts. For the thyroid and the gut, bladderwrack brings whole-food iodine and fiber that gut bacteria turn into butyrate, and a goiter record that runs from 16th-century China to the British Herbal Pharmacopoeia. Centuries of steady use for the same gland count for a lot. The modern research adds measured iodine, a rise in HDL in a placebo-controlled trial, better insulin and HbA1c on blends with its cousin knotted wrack, and a first gut-lining signal in people. The iodine and the tradition are the best established; the blood sugar, cholesterol and gut findings are promising.

Use it in gentle amounts, a pinch in food or the EU's 130 mg twice a day, alongside wild fish, eggs and a Brazil nut or two. Watching my own mother rebuild her health after a hard diagnosis taught me that the body is designed to heal when you remove what is blocking it and restore what it is missing, and the thyroid is no exception.12 Bladderwrack is one simple way to restore what it's missing.

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Bladderwrack: frequently asked questions

What does bladderwrack do for the body?

It supplies iodine, which your thyroid joins to tyrosine to make T4 and T3, and its fiber and polyphenols feed gut bacteria that made butyrate and other short-chain fatty acids from them in lab tests.4 2 5 24 In a week-long pilot in athletes, fucoidan from bladderwrack and wakame raised lysozyme, a defense protein made by the gut lining.15

Is bladderwrack good for your thyroid?

Yes, as a whole-food source of iodine in gentle amounts: dried bladderwrack averaged about 275 mcg of iodine per gram in 27 Danish samples, and it was a goiter remedy in China and in France for centuries.2 1 My Hypothyroidism Protocol ranks sea vegetables third among its top 10 thyroid foods.12

How much iodine is in bladderwrack?

About 275 mcg per gram of the dried seaweed on average, with a range of 138 to 451 mcg in 27 Danish samples, so half a gram carries roughly an adult's daily 150 mcg.2 8 Pharmacopoeia-grade powder carries 0.03% to 0.2% iodine, or 300 to 2,000 mcg per gram.9

What are bladderwrack's benefits for women?

Bladderwrack may help lengthen short or irregular cycles: in a case report of three women, dried bladderwrack lengthened every woman's cycle, from about 16 days to 31 in the woman with the shortest cycles, and in her, estrogen fell and progesterone rose.21 Women also share its thyroid, gut, blood sugar and HDL benefits, and the Eclectic physicians recommended it for menstrual problems.6 11

What are bladderwrack's benefits for men?

Bladderwrack's benefits for men are its everyday ones: iodine for the thyroid, fiber for the gut, and support for blood sugar and HDL cholesterol, and men took part in the trials behind them.2 3 17 6 No study has measured its effect on testosterone, so those shared benefits are the reason to use it.

Does bladderwrack help you lose weight?

It's registered in the EU as a traditional aid to a reduced-calorie diet for overweight adults, at 130 mg of the powder twice a day.9 Pooled trials of refined or extracted brown seaweed taken for 8 weeks or longer lowered BMI and body fat, while in one 12-week placebo-controlled trial a blend with knotted wrack added no weight loss to diet advice.25 26

How much bladderwrack should you take a day?

The EU's traditional dose, registered for weight management, is 130 mg of powdered bladderwrack twice a day, 2 hours before meals, keeping total iodine from bladderwrack products under 400 mcg a day.9 As a food, gentle amounts fit: about half a gram of the dried seaweed carries roughly a day's iodine for an adult.12 2 8

How do you take bladderwrack?

Most often as capsules of the dried powder, the form behind the EU's traditional dose of 130 mg twice a day, or as the dried, flaked seaweed in small amounts in food.9 16 It's also made into teas and tinctures, and herbal-tea blends with it have been sold in Poland since 1989.1

Is bladderwrack the same as kelp?

No, though the names overlap: bladderwrack is a Fucus seaweed, a wrack, while sugar kelp and its relatives in the kelp family, Laminariaceae, carried the most iodine of the seaweeds tested in Greenland.14 In Danish samples, sugar kelp averaged about 2,300 mcg of iodine per gram, against about 275 for bladderwrack.2 Nineteenth-century writers used the word kelp for the ash of burned seaweeds such as bladderwrack.11

Should you take sea moss, bladderwrack and burdock root together?

You can: no study has tested the three together, so take a blend the way you'd take bladderwrack alone and count its iodine toward the EU's 400 mcg a day for bladderwrack products.9 Our guides to sea moss and burdock root cover the other two.

Is bladderwrack good for your kidneys?

Its kidney use is traditional: the Eclectic physicians of the 1890s used it to ease kidney congestion and bladder irritation, and no modern study has tested that use.11 The safety section covers kidney disease.

Does bladderwrack interact with medications?

Yes: its iodine can add to thyroid medicines, lithium and amiodarone, and fucoidan from a related seaweed lengthened one clotting test, so its interaction rating is Moderate.9 35 36 37 The safety section gives one action for each.

Freshness & update log

October 23, 2026 — Rewrote the page in full under Dr. Axe's byline. The previous version, "Bladderwrack Benefits for Thyroid Health, Digestion & Healthy Aging," gave no citations or numbers; said iodine protects against certain cancers and framed a case report as lowering estrogen-related cancer risk; credited bladderwrack with lutein and zeaxanthin for the eyes and brain, with easing insect bites and burns, with relieving bloating and cramping and with cleansing or detoxing the body; said raising HDL would lower the risk of atherosclerosis and heart disease; said there is no recommended dose; listed spirulina among the seaweeds; and named NSAID, aspirin and ibuprofen interactions and iodine allergy without a source. This version keeps and sources its thyroid, digestion, weight, HDL, inflammation, joint, skin and women's-cycle uses, each at its true level of evidence; adds its traditional record from Roman, Chinese, French, British and Eclectic practice and its EU traditional-use registration; adds measured iodine and fiber, how bladderwrack works in your body, human trials on HDL, blood sugar, inflammation, joints and the gut, each labeled with its design and with blends named as blends, a Dr. Axe Score (6.1) with an interaction check (Moderate), three charts and a step diagram; replaces "no recommended dose" with the EU's traditional dose and food amounts in iodine terms; keeps burns as a traditional skin use; drops the cancer, eye, insect-bite, detox and heart-disease claims, the spirulina listing and the unsourced interactions, which we couldn't support for bladderwrack; and gathers the safety guidance in one section, with 42 references.

April 4, 2024 — Previous version published.

References

Dr. Josh Axe, DC, DNM, CNS

Doctor of Natural Medicine · Founder, DrAxe.com

Dr. Axe is a certified doctor of natural medicine, clinical nutritionist, and multiple New York Times bestselling author. He has spent 20+ years in clinical practice helping people heal at the root cause and founded one of the most-visited natural-health platforms in the world.

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This article is for educational purposes. See our medical disclaimer.

On this page

What is it?
What is it good for?
How it works
Benefits
Thyroid
Gut health
For women
How to use it
How to buy
Side effects
The bottom line
Is bladderwrack worth taking?
FAQ

Quick facts

What it isFucus vesiculosus, a brown seaweed of the rocky shores of Europe and North America
Also calledBladder wrack, sea-wrack, cut-weed, black-tang
Key compoundsIodine, fucoidan, alginate and phlorotannins
IodineAbout 275 mcg per gram dried (138 to 451 in 27 samples)
Traditional dose130 mg of powder twice a day, the EU traditional dose for weight management
Interaction checkModerate (thyroid medicines, lithium, amiodarone, blood thinners)

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