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Scientific Name(s): Laminaria bracteata Ag., Laminaria digitata (L.) Lamour., Laminaria japonica
Common Name(s): Brown algae, Devil's apron, Kelp, Kombu, Lamicel, Laminaria, Makonbu, Ne-kombu, Sea girdles

Medically reviewed by Last updated on May 17, 2024.

Clinical Overview


Laminaria has been used traditionally as a hygroscopic cervical dilator and inducer of labor or cervical preparation for dilation and evacuation, and commercial products are available for this purpose. Initial data support benefit for age-related cognitive and physical neurodegeneration with consumption of fermented Laminaria


Clinical trials are lacking to provide dosing information for uses other than mechanical cervical dilation. Fermented Laminaria japonica 1.5 g/day was consumed for 6 weeks for age-related neurodegeneration.


Use is contraindicated during pregnancy.


Laminaria dilators have been used to dilate the cervix and to induce labor in abortions. Information on the use of laminaria for other purposes during pregnancy is lacking. Avoid use.


None well documented.

Adverse Reactions

There is a risk of laminaria dilators becoming trapped and fragmenting. Cases of hypersensitivity, including anaphylaxis, have also been reported. Following excessive consumption of Laminaria, iodine-induced hypothyroidism has been reported.


Information is lacking.

Scientific Family


Laminaria, a genus of brown algae commonly known as "kelp," is found primarily in the cold waters of the North Atlantic and North Pacific oceans.Morton 1977


Laminaria for cervical dilation is used in the form of "tents," usually made of any hygroscopic (readily absorbs water) material, that are placed to maintain the opening or cause dilation. Dilators are made from the dried stems of laminaria seaweeds. When dried and rounded into a stick-like shape, the dilators are approximately 6 cm (2.5 inches) long with a diameter of 0.3 to 0.5 cm. A strong thread is attached to one end, and a collar prevents migration into the uterus. The stem is hygroscopic and can swell 3 to 5 times its original diameter within 12 to 24 hours. Other natural products used as tents for various purposes include sponges, dried corn stalks, slippery elm bark, and tupelo wood.Newton 1972 Hollow laminaria tents were developed in the 1800s to improve uterine drainage, and laminaria coated with wax was designed to release antiseptics as the wax melted.

Tents fell into disuse because of complications caused by infections. This was especially evident in tents derived from land plants because of the inability of sterilization to inactivate Clostridium spores, the causative agents of tetanus, botulism, and gas gangrene. Although laminaria from the ocean harbors relatively nonpathogenic bacteria, polluted waters and poor packaging negated the advantage. However, with the advent of ethylene oxide and gamma irradiation sterilization techniques, interest in laminaria dilators returned.

L. bracteata Ag. (L. japonica Aresch) is commonly used in soup, candy, and sushi, or is eaten with rice or as a salad. The plant is known as kombu in the Far East and is cultivated in China, Korea, and Japan.Johansen 1988


Laminarin (laminaran) is a polysaccharide found in laminaria sap. Soluble and insoluble forms are found in algae.Windholz 1983, Zvyagintseva 2003 Kelp are rich in algin, a high molecular weight polysaccharide that forms viscous colloidal solutions or gels in water. This property has led to the use of kelp derivatives as bulk laxatives.Tyler 1987 The constituents of laminaria also include iodine, potassium, magnesium, calcium, and iron.Drug & Natural Medicine 1997, Lininger 1998, van Netten 2000

Uses and Pharmacology


Animal data

Numerous components of seaweeds have demonstrated varying degrees of antioxidant capability and carcinogen inhibition in vitro and in vivo, such as sulfated polysaccharides (including fucoidan), phenolic compounds (including phlorotannins and bromophenols), and the carotenoid fucoxanthin. Diets supplemented with powdered seaweeds, including Laminaria and Porphyra spp, significantly reduced the incidence of mammary and intestinal tumors in rats.Park 2013

Cardiovascular/Metabolic syndrome

Because dietary fiber consumption has been associated with decreased energy intake and weight reduction, a 4-way double-blind, placebo-controlled, crossover trial (n=19) evaluated the effects of a preload low- and high-volume 3% alginate extract beverage (from Laminaria hyperborea and Lessonia trabeculata) on satiety, energy intake, and gastric emptying rate in healthy Danish subjects. Satiety and fullness were significantly increased, while hunger and prospective food intake were significantly decreased with the high-volume alginate treatment versus high-volume control. A significant reduction in energy intake was documented for the low-volume, but not the high-volume, treatment. High-volume alginate preload also resulted in a significant (40%) reduction in glucose response, whereas neither treatment resulted in changes to blood pressure or heart rate.Georg Jensen 2012

Cervical ripening

Laminaria dilators have been used to dilate the cervix and to induce labor in abortions. When inserted into the cervix, laminaria dilators absorb surrounding moisture and gradually swell to a diameter of approximately one-half inch. While most of the swelling occurs in the first 4 to 6 hours, it may continue for up to 24 hours. Because this is a gradual process, the patient rarely notices pain. At the same time, the cervix is induced to ripening (becoming soft and flexible). The effect is often limited to local cervical ripening; however, stimulation of the cervix can induce labor.

The mechanism of action may be similar to that of a foreign body that, when inserted into the cervical canal, disturbs the normal chorioamniotic balance and initiates a cascade of prostaglandin synthesis. This in turn has myometrial-contracting and cervical-ripening effects.Kazzi 1982 Mediation by arachidonic acid has been suggested, but is not supported by evidence.Crawford 1976 Cervical dilation may also be the result of partial placental detachment induced by laminaria.Jonasson 1989

Clinical data

A Cochrane review of mechanical methods of labor induction considered trials of laminaria versus placebo, prostaglandins, oxytocin, or extra-amniotic infusion. Most trials were small and evaluated different outcomes, making comparisons difficult. Thus, the review used risk of cesarian delivery as the comparator outcome measure. The lack of blinding in these trials must also be considered a potential source of bias.Boulvain 2001

In trials of laminaria versus placebo, no evidence exists of increased risk of cesarian delivery. Rates of cesarian delivery were the same for laminaria versus oxytocin and for laminaria versus extra-amniotic infusion. Likewise, in trials versus prostaglandins, the risk of cesarian delivery was the same for both groups; however, laminaria caused less hyperstimulation with fetal heart rate changes. No added benefit was found in trials of laminaria added to prostaglandins or to oxytocin.Boulvain 2001

Trials subsequent to the Cochrane review, which included trials up to 2001, have largely found similar results.Almog 2005 More recent trials have evaluated laminaria versus misoprostol and mifepristone, finding similar efficacy, but showing an increase in cost, induction times, and pain associated with laminaria.Borgatta 2005, Darwish 2004, Edelman 2006, Prairie 2007 The lack of blinding remains a methodological issue.

The potential exists for adverse outcomes with laminaria dilator use, especially infectious morbidity; endometritis, fetal sepsis, septic shock, and anaphylaxis have been reported.Kazzi 1982, Kim 2003, Knowles 2002, Lin 2006 A review of laminaria in cervical ripening found no difference in maternal infection rates for trials reporting infection-related outcomes, but the number of trials was small.Heinemann 2008 A further review concluded that serious infection and anaphylaxis were rare with commercial laminaria devices.Lichtenberg 2004 In a review of trials using laminaria in mid-trimester abortions, no increased risk of clinically important subsequent pregnancy complications was found.Jackson 2007

The Society of Family Planning (SFP) clinical guideline for cervical preparation for second-trimester surgical abortion prior to 20 weeks’ gestation (2014) recommends in favor of cervical preparation with osmotic dilators (eg, laminaria) prior to second-trimester dilation and evacuation (D&E) (Level A). Recommendations are based on safety and efficacy, lack of increased infections or morbidity, and increased preoperative dilation compared to mifepristone or misoprostol; laminaria is not preferred for same-day dilator placement and D&E (Level A). Prior to 20 weeks’ gestation, a single set of osmotic dilators may achieve adequate cervical preparation (Level B). Overnight placement of osmotic dilators is recommended after 18 weeks’ gestation; the choice of number and type of osmotic dilators and length of preoperative treatment depend on gestation age, provider experience, and patient risk factors (Level C).Fox 2014


Clinical data

The effects of Laminaria on neurodegeneration related to aging was investigated in a double-blind, randomized, placebo-controlled trial of 60 moderately active Korean seniors (mean age, 73 years) who ingested fermented Laminaria japonica 1.5 g/day or placebo for 6 weeks. The specialized fermentation process utilized Lactobacillus brevis BJ20 to increase the GABA content of the seaweed solution; mean GABA content was 5% (54.5 mg/g of fermented laminaria). Several neuropsychological and physical fitness improvements were seen in the Laminaria group compared to worsening of most outcomes in the placebo group. Cognitive improvements were observed in Mini-Mental State Examination scores (P=0.007), numerical memory (P=0.039), visual and spatial reasoning (P=0.000), and visual sensory memory (P<0.01). The Laminaria group also demonstrated significant improvements in both 6-minute walk tests (P<0.001, P<0.05), a mobility test (P<0.000), antioxidant capacity (P<0.05), and the growth-related factors IGF-1 (P<0.001) and BDNF (P<0.05).Reid 2018

Other uses

Sulfated polysaccharides from marine Laminaria cichoroides exert anticoagulant activity similar to that of heparin, but clinical relevance is unclear.Drozd 2006, Yoon 2007

The basal parts of the blades of L. japonica and L. angustata have been used as a hypotensive agent (ne-kombu) in Japanese folk medicine.Miyai 2008 Chemical analysis of the blades suggests that histamine and the amino acid laminine may be responsible for this hypotensive effect.Chiu 1997, Funayama 1981

Alginate-containing algae reduce the absorption of radioactive strontium in animals and humans and are used in the management of radioactive intoxications.Gong 1991


Cervical dilation

Clinical trials are lacking to provide dosing information for uses other than mechanical cervical dilation.

Age-related cognitive and physical neurodegeneration

Fermented Laminaria japonica 1.5 g/day was consumed for 6 weeks.Reid 2018

Pregnancy / Lactation

Laminaria dilators have been used to dilate the cervix and to induce labor in abortions. Information on the use of laminaria for other purposes during pregnancy is lacking. Avoid use.


None well documented.

Adverse Reactions

There is a risk of laminaria dilators becoming trapped and fragmenting.Borgatta 1991, Lichtenberg 2004 Synthetic laminaria dilators prepared from hydrophilic polymers provide increased levels of structural stability.Chvapil 1982

Increases in serum thyrotropin were observed in healthy volunteers who consumed kombu 15 g daily for 7 to 10 days. Long-term ingestion (55 to 87 days) led to abnormally elevated serum thyrotropin levels, but these returned to normal on discontinuation of consumption. The effect was attributed to the iodine content of the seaweed. Reports of hypothyroidism exist among Japanese populations, but causality has not been established in most cases.Miyai 2008 However, a case of iodine-induced hypothyroidism was reported in a 13-year-old Japanese girl with anorexia nervosa. Her total daily iodine intake was 34,700 mcg/day that resulted from daily intake of Kombu kelp (20 g/day), Japanese kelp and its broth. Her thyroid function improved within a week of stopping the Kombu kelp.Kita 2019

A case report of laminaria hypersensitivity was followed up with a review conducted through August 2014 of reported cases of hypersensitivity to laminaria. Of the 10 reactions documented, 8 met the criteria for anaphylaxis. No deaths in the female patients were reported and most patients experienced prompt resolution with antihistamines and corticosteroids.Sierra 2015


Information is lacking.

Index Terms



This information relates to an herbal, vitamin, mineral or other dietary supplement. This product has not been reviewed by the FDA to determine whether it is safe or effective and is not subject to the quality standards and safety information collection standards that are applicable to most prescription drugs. This information should not be used to decide whether or not to take this product. This information does not endorse this product as safe, effective, or approved for treating any patient or health condition. This is only a brief summary of general information about this product. It does NOT include all information about the possible uses, directions, warnings, precautions, interactions, adverse effects, or risks that may apply to this product. This information is not specific medical advice and does not replace information you receive from your health care provider. You should talk with your health care provider for complete information about the risks and benefits of using this product.

This product may adversely interact with certain health and medical conditions, other prescription and over-the-counter drugs, foods, or other dietary supplements. This product may be unsafe when used before surgery or other medical procedures. It is important to fully inform your doctor about the herbal, vitamins, mineral or any other supplements you are taking before any kind of surgery or medical procedure. With the exception of certain products that are generally recognized as safe in normal quantities, including use of folic acid and prenatal vitamins during pregnancy, this product has not been sufficiently studied to determine whether it is safe to use during pregnancy or nursing or by persons younger than 2 years of age.

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Further information

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