Hai Zao
StarSargassum pallidum (Turn.) C.Ag. / Sargassum fusiforme (Harv.) Setch.
Traditionally used for
- Cough & breathing
- Digestion
- Urinary & fluids
☯ TCM Properties
Dissipates Nodules and Softens Hardness; Dissolves Phlegm; Promotes Urination and Reduces Edema
Traditional Chinese Uses
Hai Zao (sargassum seaweed) is a cold, salty herb from the sea that softens hardened accumulations and resolves Phlegm — especially hardened Phlegm-type nodules of the neck and thyroid. It is used for goiter, cervical lymphadenopathy, testicular swelling, and abdominal masses from Phlegm accumulation. It also promotes fluid excretion to reduce certain types of edema. Together with Kun Bu (kelp), it forms the classical combination for thyroid and neck nodule conditions.
Relationships
Full-screen graph →Click a node for details · double-click to expand it · Ctrl/⌘ + scroll or two fingers to zoom and pan.
Botanical Description
Hai Zao is derived from species of Sargassum, a genus of brown macroalgae in the family Sargassaceae (order Fucales), most commonly Sargassum pallidum and S. fusiforme in Chinese coastal waters. These are not true plants but multicellular brown algae attached to rocky substrates in the intertidal and shallow subtidal zones of the Pacific along the coasts of China, Korea, and Japan. The thallus consists of a discoid or claw-like holdfast, a short cylindrical stipe, and a much-branched frond bearing flattened, leaf-like blades and numerous small, spherical, gas-filled bladders (pneumatocysts) that provide buoyancy. Color ranges from olive-green to yellow-brown owing to chlorophylls masked by fucoxanthin. Reproductive structures called receptacles develop in the upper branches. The species form extensive submerged meadows that provide habitat for marine fauna, and the whole dried thallus is harvested for use.
Active Constituents
Iodine (iodide and organically bound iodine)
Halogen trace elementConcentration: Species-dependent and highly variable. A 2020-2024 Korean survey of 348 seaweed samples measured hijiki (Sargassum fusiforme) at a mean 526.6 mg/kg dry weight, range 159.2 to 1547.7 mg/kg; sea tangle (Saccharina japonica, the Kun Bu source) was far higher at a mean 2432.1 mg/kg
This is the constituent that makes Hai Zao clinically consequential. A single gram of dried Sargassum can carry several hundred micrograms to over a milligram of iodine, against an adult reference intake of 150 micrograms and a tolerable upper level of 1100 micrograms per day. Excess iodine causes both iodine-induced thyrotoxicosis (in nodular goitre and autonomous nodules) and iodine-induced hypothyroidism (through failure to escape the Wolff-Chaikoff effect), and both have been reported after seaweed ingestion. The variability between batches is wide enough that dose cannot be inferred from weight alone.
Inorganic arsenic (arsenate and arsenite)
Inorganic metalloid contaminantConcentration: Sargassum fusiforme is an arsenic accumulator: total arsenic reached 84.37 mg/kg dry weight at the mature growth stage, with inorganic arsenic about 68 percent of the total and arsenate more than half of the inorganic fraction
Unlike most seaweeds, which store arsenic as relatively benign arsenosugars, brown algae of this genus carry a large share as inorganic arsenic, a group 1 human carcinogen. Feeding rats a 3 percent hijiki diet produced marked arsenic accumulation in blood and tissues with biochemical changes consistent with arsenic poisoning. Food agencies in the United Kingdom, Canada, the United States, Australia, New Zealand and Singapore have advised consumers against eating hijiki for this reason. Repeated boiling in fresh water removes a large fraction, so decocted material is lower in arsenic than raw powder or granules.
Fucoidan (sulfated fucose-rich polysaccharide)
Sulfated polysaccharideConcentration: A major cell-wall polysaccharide of brown algae, typically several percent of the dry weight
Strongly anticoagulant in vitro, acting mainly through heparin cofactor II rather than antithrombin, but roughly 20 to 30 times weaker than heparin by weight. In a single-blinded pilot study of 20 volunteers given 3 g of a 75 percent fucoidan preparation for 12 days, no clear in vivo effect on haemostasis appeared, attributed to poor intestinal absorption. It also carries most of the immunomodulatory and antitumour activity reported for Sargassum extracts.
Alginic acid and alginates
Polyuronide polysaccharideConcentration: A principal structural polysaccharide of the thallus
Gives the decoction its viscosity and accounts for the bulk-forming and mildly laxative character of the drug. Alginates bind divalent and heavy metal cations in the gut, which is the basis of the historic use of alginate preparations to reduce radiostrontium absorption; the same property means Hai Zao can reduce absorption of co-administered mineral supplements and some drugs taken at the same time.
Sargassum pallidum polysaccharide
HeteropolysaccharideConcentration: Purified fractions characterised from Sargassum pallidum
Purified polysaccharide from Sargassum pallidum showed antitumour and immune-enhancing activity in cell and rodent models, consistent with earlier work on purified polysaccharides of the same species. Preclinical only; there is no human trial of a Sargassum polysaccharide for any oncological indication.
Phlorotannins (polyphenols)
Polyphenol (phloroglucinol oligomers)Concentration: Extracted and quantified from Sargassum pallidum
The polyphenol fraction of Sargassum pallidum inhibits digestive and metabolic enzymes in vitro, which is the usual mechanistic account for the antioxidant and glucose-lowering effects attributed to brown algae. In vitro only.
Mannitol
Sugar alcoholConcentration: A characteristic storage carbohydrate of brown algae, sometimes visible as a white bloom on dried thallus
Osmotically active and poorly absorbed; contributes to the mild diuretic and stool-softening character noted for the drug and can cause loose stools at high dose.
⚠ Drug Interactions
Radioiodine (iodine-131) diagnostic scanning or ablation therapy
Stable iodine from seaweed competes with iodine-131 for the sodium-iodide symporter and expands the body iodine pool, so less of the administered radioiodine is trapped by thyroid tissue. Low-iodine preparation is standard practice for exactly this reason: the American Thyroid Association advises limiting intake to about 50 micrograms of iodine per day, and low-iodine diet instructions from major centres name seaweed, kelp and dulse-containing supplements specifically. A cohort study of iodine depletion before radioiodine therapy found that patients whose urinary iodine excretion was still 200 micrograms per day or more at the time of treatment had a significantly higher risk of progression than those below that threshold. A single gram of Sargassum can exceed a whole day of the permitted iodine allowance many times over.
Clinical note: Stop Hai Zao, Kun Bu and any other seaweed at least two to four weeks before a radioiodine scan or ablation and do not restart until the treating nuclear medicine team says so. Tell the endocrinology team the patient has been taking seaweed even if it has been stopped, because the iodine pool takes weeks to clear.
Levothyroxine and other thyroid hormone replacement
A large exogenous iodine load can drive thyroid function either way. In a 45-year-old woman with no previous thyroid disease, a kelp-containing marketed diet produced hyperthyroidism lasting two months followed by overt hypothyroidism, a pattern the authors attributed to iodine-induced thyrotoxicosis followed by prolonged blockade of sodium-iodide symporter activity. In a patient already on replacement, that shifts the dose requirement without warning, and the resulting TSH change is easily misread as non-adherence. The interaction is with the iodine, not with any specific Sargassum constituent, so it applies to Kun Bu and other seaweeds equally.
Clinical note: Check TSH and free T4 before starting and again six to eight weeks after starting or stopping Hai Zao. In a patient with a stable levothyroxine dose and a documented autoimmune thyroiditis, prefer a non-iodine phlegm-transforming substitute.
Antithyroid drugs (carbimazole, methimazole, propylthiouracil)
Thionamides block thyroid peroxidase, but a large iodine load supplies excess substrate and can both blunt and, on withdrawal, rebound the response. Iodine-induced thyrotoxicosis after herbal seaweed is documented directly: a 39-year-old woman with multinodular goitre developed hyperthyroidism after a prescribed herbal tea containing large amounts of kelp, Sargassum and kombu. A patient on antithyroid drugs who adds Hai Zao is being loaded with the very substrate the drug is trying to withhold.
Clinical note: Do not combine Hai Zao with antithyroid drug therapy. If a patient on carbimazole or propylthiouracil turns out to have been taking a seaweed-containing formula, stop the seaweed and repeat thyroid function tests rather than adjusting the drug dose first.
Amiodarone
Amiodarone is about 37 percent iodine by weight and already delivers a daily free-iodide load orders of magnitude above physiological need, which is why amiodarone-induced thyrotoxicosis and hypothyroidism are common. Adding seaweed iodine on top is pharmacologically additive. There is no case series of the specific combination, so this is reasoning from established amiodarone thyroid toxicity rather than direct evidence.
Clinical note: Avoid Hai Zao in any patient taking or recently withdrawn from amiodarone; the iodine load persists for months after the drug is stopped.
Lithium
Lithium inhibits thyroid hormone release and is a recognised cause of goitre and hypothyroidism. Excess iodine independently causes hypothyroidism through failure to escape the Wolff-Chaikoff effect. The two mechanisms are additive in principle; no clinical reports of the specific combination were found.
Clinical note: If Hai Zao is used at all in a lithium-treated patient, monitor TSH as a matter of course rather than only when symptoms appear.
Gan Cao (Glycyrrhizae Radix et Rhizoma)
Hai Zao is named against Gan Cao in the eighteen incompatibilities couplet (zao ji sui yuan ju zhan cao), yet the classical goitre formula Hai Zao Yu Hu Tang from Chen Shigong's Wai Ke Zheng Zong deliberately combines them, and Li Shizhen defended the pairing on the grounds that hard accumulations cannot be shifted by mild drugs. Modern rat work has tested the pair directly rather than assuming either position. In propylthiouracil-induced goitre rats, decoctions built on either Sargassum species produced an antigoitre effect through the hypothalamus-pituitary-thyroid axis and inhibition of thyroid peroxidase gene expression, and the licorice combination did not produce the general toxicity the prohibition implies. What the same work did find is that the Sargassum species is the variable that matters: Sargassum fusiforme induced hepatorenal injury while Sargassum pallidum showed a liver and kidney protective effect, a difference that is invisible in commerce because the two are not clearly distinguished in clinical use. Later studies extended the same comparison to the Glycyrrhiza variety used.
Clinical note: The classical prohibition is not supported as a general toxicity signal, but do not treat that as licence: source Sargassum pallidum rather than Sargassum fusiforme where the supplier can specify, since the hepatorenal signal and the higher arsenic burden both attach to fusiforme. Watch for glycyrrhizin's own pseudoaldosteronism, which is a separate and better-established hazard than the classical pairing.
Warfarin, direct oral anticoagulants and antiplatelet drugs
Fucoidan from brown algae is a potent in vitro anticoagulant acting largely through heparin cofactor II. The obvious inference is additive bleeding risk, but the one human study addressing it found otherwise: in a single-blinded pilot in 20 volunteers, 3 g daily of a 75 percent fucoidan preparation for 12 days produced no obvious in vivo effect on haemostasis, which the authors attributed to low intestinal absorption. The theoretical concern therefore deserves recording but not alarm.
Clinical note: No routine dose adjustment or extra INR monitoring is warranted on current evidence. Record the herb and ask about bruising at follow-up as with any new supplement.
Oral mineral supplements and drugs with narrow absorption windows taken concurrently
Alginates are viscous cation-binding polyuronides; the same property exploited in alginate raft antacids and in alginate preparations used to reduce radiostrontium uptake will bind iron, calcium and other divalent cations in the gut lumen. No specific clinical study of Hai Zao and a named drug was found.
Clinical note: Separate the decoction from iron, calcium or zinc supplements by at least two hours.
Dosage
| Form | Amount | Frequency | Duration | Population | Notes |
|---|---|---|---|---|---|
| decoction | 6–12 g | Daily | — | — | 中国药典 2020 【用法与用量】6～12g。 【注意】不宜与甘草同用。 【性味与归经】苦、咸，寒。归肝、胃、肾经。 — Chinese Pharmacopoeia 2020, quoted verbatim; route and cautions preserved. Replaces a cleared category-filler value. |
Dui Yao — Herb Pairs
The classical two-herb combinations this herb appears in, each with an action neither herb has alone.
Mutually reinforce softening of hardness, dissipating of nodules and dispelling of phlegm, for goiter and scrofula.
Hai Zao is traditionally listed as incompatible with Gan Cao (shi ba fan).
Named pairing — Zhong Yao Xue national textbook, pei wu discussion
Evidence Tier
Moderate evidence · 10 studiesRecorded studies by study design, strongest design at the top. This is a study-design tier only, not a GRADE rating: it does not weigh risk of bias, consistency or precision.
Systematic review / meta-analysis
0
Randomized controlled trial
0
Other clinical trial
1
1 verified · 0 unverified
Observational / case report
4
2 verified · 2 unverified
Show 4 studies
- Iodine-Induced Thyrotoxicosis After Ingestion of Kelp-Containing Tea
- Thyroid dysfunction following a kelp-containing marketed diet
- The utility of low-iodine diet in preparation for thyroid cancer therapy with radioactive iodine—A cohort study
- Analysis and Risk Assessment of Total Iodine Content in Edible Seaweeds in South Korea
In vitro / animal
5
2 verified · 3 unverified
Show 5 studies
- Comparative Efficacy and Toxicity of Different Species of Sargassum in Haizao Yuhu Decoction in PTU-Induced Goiter Rats
- Do Different Species of Sargassum in Haizao Yuhu Decoction Cause Different Effects in a Rat Goiter Model?
- Haizao Yuhu decoctions including three species of glycyrrhiza protected against propylthiouracil-induced goiter with hypothyroidism in rats via the AMPK/mTOR pathway
- Toxicity of so-called edible hijiki seaweed (Sargassum fusiforme) containing inorganic arsenic
- ARSENIC CONTENTS AND SPECIATION AT DIFFERENT GROWTH STAGES OF SARGASSUM FUSIFORME [HARV.] SETCHELL (HIJIKI), AN EDIBLE SEAWEED
Other / unclassified
0
Verified: design read from PubMed for a DOI that resolves to the cited paper Unverified: taken from the study's recorded description
Clinical Studies
Iodine-Induced Thyrotoxicosis After Ingestion of Kelp-Containing Tea
A 39-year-old woman with multinodular goitre developed clinically overt hyperthyroidism after taking a prescribed herbal tea containing large quantities of kelp, Sargassum and kombu. The case is the closest published evidence to the drug as actually used in Chinese herbal practice, since the preparation was a herbal prescription rather than a supplement, and it identifies pre-existing nodular goitre as the risk setting.
Thyroid dysfunction following a kelp-containing marketed diet
A 45-year-old woman with no previous thyroid disease developed hyperthyroidism shortly after starting a kelp-containing diet; it lasted about two months and was followed by overt hypothyroidism. The authors read this as iodine-induced thyrotoxicosis followed by prolonged blockade of sodium-iodide symporter activity from excess iodine, which is the biphasic pattern practitioners should expect rather than a single predictable direction of change.
Comparative Efficacy and Toxicity of Different Species of Sargassum in Haizao Yuhu Decoction in PTU-Induced Goiter Rats
Rats with propylthiouracil-induced goitre were treated for 28 days with Haizao Yuhu Decoction built on either Sargassum fusiforme or Sargassum pallidum, both combined with licorice in defiance of the classical prohibition. Both versions produced an antigoitre effect through changes in the hypothalamus-pituitary-thyroid axis and inhibition of thyroid peroxidase gene expression. The toxicity finding is the important one: the Sargassum fusiforme version induced hepatorenal injury while the Sargassum pallidum version showed a liver and kidney protective effect. No retraction notice or expression of concern was found for this article.
Do Different Species of Sargassum in Haizao Yuhu Decoction Cause Different Effects in a Rat Goiter Model?
A follow-up rat goitre study by the same group re-examining whether the two pharmacopoeial Sargassum species behave differently inside the classical formula. It reinforces the practical point that Hai Zao is not one drug: what the supplier ships as Sargassum determines both the efficacy profile and the organ toxicity. No retraction notice or expression of concern was found for this article.
Haizao Yuhu decoctions including three species of glycyrrhiza protected against propylthiouracil-induced goiter with hypothyroidism in rats via the AMPK/mTOR pathway
The same classically incompatible Sargassum and licorice pair tested with three different Glycyrrhiza species in propylthiouracil-induced goitre with hypothyroidism. The formulations were protective and worked through AMPK/mTOR signalling; the study is further evidence that the pairing does not behave as a general toxic combination in rodents, while leaving the species-identity question open.
Toxicity of so-called edible hijiki seaweed (Sargassum fusiforme) containing inorganic arsenic
Rats fed a 3 percent hijiki diet accumulated arsenic markedly in blood and tissues and developed raised body temperature and abnormal blood biochemistry including elevated plasma alkaline phosphatase and inorganic phosphorus, consistent with arsenic poisoning. This is the experimental basis for the food-safety advisories against hijiki, and it applies directly to Sargassum fusiforme as a medicinal source of Hai Zao.
The utility of low-iodine diet in preparation for thyroid cancer therapy with radioactive iodine—A cohort study
Cohort study of iodine depletion before radioiodine therapy for thyroid cancer. Patients whose urinary iodine excretion was still 200 micrograms per day or more at the time radioiodine was given had a significantly higher risk of disease progression than those below that level. It is the quantitative underpinning for treating a seaweed-containing prescription as a genuine obstacle to radioiodine therapy rather than a dietary nicety.
Pilot clinical study to evaluate the anticoagulant activity of fucoidan
Single-blinded trial in 20 volunteers: 10 took 3 g of guar gum capsules and 10 took 3 g of 75 percent fucoidan capsules for 12 days. Despite very strong in vitro anticoagulant activity, no obvious in vivo effect on haemostasis appeared, which the authors attributed to low intestinal absorption. Useful negative evidence against the widely repeated claim that seaweed fucoidan poses a practical bleeding risk when taken by mouth.
Analysis and Risk Assessment of Total Iodine Content in Edible Seaweeds in South Korea
Survey of 348 samples of five seaweed species collected from 12 Korean coastal regions between 2020 and 2024, analysed by ICP-MS. Hijiki (Sargassum fusiforme) averaged 526.6 mg/kg dry weight of iodine with a range of 159.2 to 1547.7 mg/kg, roughly a tenfold spread within one species; sea tangle averaged 2432.1 mg/kg. The spread is the clinically important finding, because it means iodine dose from a fixed weight of Hai Zao cannot be predicted.
ARSENIC CONTENTS AND SPECIATION AT DIFFERENT GROWTH STAGES OF SARGASSUM FUSIFORME [HARV.] SETCHELL (HIJIKI), AN EDIBLE SEAWEED
Arsenic speciation across the growth cycle of Sargassum fusiforme. Total arsenic reached 84.37 mg/kg dry weight at the mature stage, with inorganic arsenic accounting for 68 percent of the total and arsenate for more than half of the inorganic fraction. This is an analytical survey rather than a biological experiment; it establishes that the arsenic in this species is predominantly in the toxic inorganic forms rather than the arsenosugars typical of other seaweeds.
⚠ Safety & Contraindications
Contraindications
It is not suited to combine with Radix et Rhizoma Glycyrrhizae ( gan cao ) to use. And its use is prohibited in patients with deficiency-cold of the spleen and stomach and dampness stagnation.
Source: Xi S, Gong Y. Essentials of Chinese Materia Medica and Medical Formulas. Academic Press/Elsevier, 2017, pp. 267–277.
⚠ Rule-Based Cautions
These entries come from the deterministic rule tables that gate Verscienta's formula tools — classical pair prohibitions, pregnancy and lactation contraindications, and dose ceilings.
Incompatibilities (十八反 / 十九畏)
- 十八反: Gan Cao × Hai Zao — avoid combining with Gan Cao / Glycyrrhiza / Licorice / Liquorice
Historical Texts
Shen Nong Ben Cao Jing (Divine Husbandman's Classic of the Materia Medica)
Han dynasty, c. 200 CERu Men Shi Qin (Confucians' Duties to Their Parents), Zhang Congzheng (Zhang Zihe)
Jin dynasty, 13th centuryWai Ke Zheng Zong (Orthodox Lineage of External Medicine), Chen Shigong
Ming dynasty, 1617Ben Cao Gang Mu (Compendium of Materia Medica), Li Shizhen
Ming dynasty, 1596References
- Liu L, Heinrich M, Myers S, Dworjanyn SA. Towards a better understanding of medicinal uses of the brown seaweed Sargassum in Traditional Chinese Medicine: A phytochemical and pharmacological review . Journal of Ethnopharmacology (2012) [DOI]
- Gao Y, Li Y, Niu Y, Ju H, Chen R, Li B, et al.. Chemical Characterization, Antitumor, and Immune-Enhancing Activities of Polysaccharide from Sargassum pallidum . Molecules (2021) [DOI]
- Ye H, Wang K, Zhou C, Liu J, Zeng X. Purification, antitumor and antioxidant activities in vitro of polysaccharides from the brown seaweed Sargassum pallidum . Food Chemistry (2008) [DOI]
- Jiang H, Kong L, Tang H, Wang Z, Liu C, Zhang J, et al.. Study on the preparation and enzyme inhibitory activity of polyphenols from Sargassum pallidum . PLOS ONE (2024) [DOI]
- Teas J, Pino S, Critchley A, Braverman LE. Variability of Iodine Content in Common Commercially Available Edible Seaweeds . Thyroid (2004) [DOI]
- Li M, Xiu L, Liao W, Ren Y, Huo M, Liu H, et al.. Exploring the effect and mechanism of Haizao Yuhu decoction containing three variants of glycyrrhiza on goiter using an integrated strategy of network pharmacology and RNA sequencing . Journal of Ethnopharmacology (2023) [DOI]
This information is for educational purposes only and is not intended to replace professional medical advice. Always consult a qualified healthcare provider before using any herbal remedy, especially if you are pregnant, nursing, or taking medications.
📝 Notes
Public notes from the community and your own private notes on Hai Zao.
No notes yet.