Hǎi Zǎo (海藻) — Sargassum / Seaweed

On this page

1. Overview
2. Properties
3. Actions and indications
4. Key formulas
5. Modern research
6. Incompatibilities
7. Cautions and contraindications
8. Treatment at my clinic

1. Overview

Hǎi Zǎo (海藻) — the dried thallus of Sargassum pallidum (or S. fusiforme), the brown seaweed known in English as sargassum — is the principal Chinese herb for goitre, thyroid nodules and phlegm nodules in the neck. It belongs to the “Herbs that resolve Phlegm and soften hardness” category of the Chinese Materia Medica. Its salty flavour is the classical TCM driver of its softening-hardness action: salt enters the Kidney and breaks up palpable accumulations of Phlegm. It is used in Chinese herbal medicine as a component of classical formulas and in tailored prescriptions.

I prescribe Hǎi Zǎo as part of bespoke herbal formulas from pharmaceutical-grade granules sourced from Sun Ten in Taiwan. Online consultations are available for patients who cannot attend my clinic in person.

2. Properties

3. Actions and indications

Principal actions

1. Softens hardness and dissolves nodules — the headline action
2. Resolves Phlegm accumulations, particularly the firm, palpable kind
3. Promotes urination and reduces oedema

Indications

1. Goitre — the principal classical indication; the seaweed iodine content is directly relevant
2. Thyroid nodules, both benign and adenomatous
3. Scrofula (cervical lymphadenitis) and other Phlegm nodules in the neck
4. Lumps, swellings and benign cysts in the breast or testis with Phlegm-stagnation pattern
5. Oedema, urinary retention, ascites with Damp accumulation

4. Key formulas containing Hǎi Zǎo

• Hai Zao Yu Hu Tang (Sargassum Decoction for the Jade Flask) — the principal classical formula for goitre and thyroid nodules; the seaweed pair Hai Zao + Kun Bu (Laminaria) provides iodine and softening action
• Nei Xiao Luo Li Wan (Internally Reduce Scrofula Pill) — for cervical lymph node swellings (scrofula) and Phlegm nodules
• Si Hai Shu Yu Wan (Four Seas Pill to Smooth Stagnation) — combines Hai Zao with Kun Bu, Hai Dai and Hai Piao Xiao for stubborn thyroid swellings

See the full Chinese herbal medicine formula directory for detailed information on the classical formulas.

5. Modern research

Sargassum species contain iodine (the active constituent most relevant to thyroid action), alginates, fucoidan (a sulfated polysaccharide with documented anticoagulant, anti-inflammatory and immunomodulatory effects), and several phlorotannin compounds. Modern research has documented anti-thyroid-nodule effects in animal models, alongside anticoagulant, lipid-lowering and antioxidant activity from the fucoidan and polysaccharide fractions. The iodine content of Hai Zao is the most direct mechanistic link to its classical role in goitre — iodine deficiency is a primary cause of endemic goitre, and the Chinese herbal tradition arrived empirically at the seaweed remedy long before the iodine mechanism was understood.

6. Incompatibilities

Classical Shi Ba Fan (Eighteen Antagonisms): Hǎi Zǎo is listed as antagonistic with Gan Cao (Liquorice) in the classical Shi Ba Fan. However, in classical clinical practice the two are frequently combined — Hai Zao Yu Hu Tang itself pairs Hai Zao with Gan Cao deliberately, on the principle that the “mutual antagonism” can in some pathologies be turned to therapeutic advantage (the friction between opposing actions breaks up stubborn Phlegm stagnation). This is one of the most famous examples of clinically validated departure from the classical antagonism list. The combination should be used only by experienced practitioners and within established classical formulas.

As with every Chinese herb it should be prescribed only as part of a balanced formula by a registered Chinese herbalist (RCHM).

7. Cautions and contraindications

Hai Zao is well-tolerated at standard doses but the iodine content means thyroid status must be considered in every patient before prescribing.

• Caution with hyperthyroidism, Graves’ disease and autoimmune thyroiditis — excess iodine can destabilise these conditions; use only with specialist supervision and ideally with thyroid function monitoring
• Caution in pregnancy — high-iodine intake can affect fetal thyroid development
• Caution with thyroid medications — iodine intake may alter the dose requirement for levothyroxine and other thyroid drugs
• Caution with anticoagulants — the fucoidan content has documented anticoagulant activity; coordinate with the patient’s prescriber if they are on warfarin, DOACs or aspirin
• Caution with lithium — iodine and lithium can synergise to suppress thyroid function

Pattern contraindications

Contraindicated in Spleen and Stomach Yang deficiency with Cold-Damp — the salty, cold nature of Hai Zao further injures the digestive Yang.

Modern drug interactions

Avoid combination with levothyroxine, anticoagulants (warfarin, DOACs, aspirin in clinically significant doses) and lithium without specialist supervision. Tell your doctor and your herbalist about all medications.

Important: Chinese herbs should always be prescribed by a fully qualified herbalist who is a member of the Register of Chinese Herbal Medicine (RCHM). Never self-prescribe Hai Zao if you have a thyroid condition. Dr (TCM) Attilio D’Alberto is a member of the RCHM with over 25 years of clinical experience.

8. Treatment at my clinic

I prescribe Hǎi Zǎo as part of tailored herbal formulas for goitre, thyroid nodules, scrofula and Phlegm-nodule patterns — most commonly within the classical Hai Zao Yu Hu Tang framework, modified to the patient’s constitution and thyroid status. Patients with diagnosed thyroid disease are managed alongside their endocrinologist or doctor, with thyroid function monitoring as appropriate.

I see patients in person at my clinic in Wokingham, Berkshire. Online Chinese herbal medicine consultations are available throughout the UK and internationally. Visit the prices page for consultation fees.

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