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Traditional Chinese medicine

CoixCoix lacryma-jobi var. ma-yuen

A pale grain eaten as food and used in spleen formulas; the only gut-adjacent human data we found are 11 men eating 160 g a day for 7 days.

Botanical name
Coix lacryma-jobi var. ma-yuen
Part used
seed (hulled kernel)
Also called
pinyin Yi yi ren (薏苡仁); Job's tears, Adlay, Chinese pearl barley, Coicis semen
Used in
Traditional Chinese medicine
Taken for
Loose stools and diarrhea, Bloating, Appetite
Sold as
dried kernels, powder, tea, decoction, in formulas

What is meant by coix

Coix is the hulled seed of Coix lacryma-jobi var. ma-yuen (Romanet du Caillaud) Stapf, a grass cultivated in many regions of China. The seed is a rounded, pale grain, and English-language labels often call it Job’s tears, adlay or Chinese pearl barley. A review calls it both a food and a medicinal resource and lists fatty acids, polysaccharides, sterols, triterpenes, lignans, flavonoids and other compounds among its constituents.

In the kitchen the kernels are simmered in congee, soups, sweet desserts and teas. In the pharmacy they are sold dried for decoctions, or ground. Coix is one of the ten ingredients of Shen Ling Bai Zhu San, a Song-dynasty formula that the texts use for what they call spleen weakness with loose stools.

In the traditions

Traditional Chinese medicine (about TCM)

Yi yi ren is classed in the Chinese materia medica as sweet and bland and cool to slightly cold, entering the spleen, stomach and lung channels. The tradition says it promotes urination and leaches out what the texts call dampness, supports the spleen and stops diarrhea, clears heat and drains pus. In the tradition’s vocabulary it is used for loose stools and a feeling of heaviness that the texts attribute to spleen weakness with dampness. It is a mild, food-like herb, and in Shen Ling Bai Zhu San it works alongside Chinese yam, lotus seed and poria. TCM texts also advise caution in pregnancy because of its draining action. These are the tradition’s own statements, from the standard English materia medica, not findings about the body.

What the plant contains

The seed holds fatty acids and esters, polysaccharides, sterols, alkaloids, triterpenes, tocopherols, lactams, lignans, phenols and flavonoids, according to a review. That review credits it in laboratory and animal studies with effects on blood sugar, liver function, intestinal microbiota, spleen function and inflammation. These are preclinical findings, and the same review stresses that clinical trials, toxicology and pharmacokinetic data are still needed.

What has been tested in people

We could not find a randomized trial of coix alone for a gut symptom. The nearest human data are a small Japanese study of healthy men. Nineteen men were divided into two groups; 11 ate cooked coix seed at 160 g a day for 7 days and eight had no intervention. After the week the coix group had more intestinal Faecalibacterium, a bacterial genus, and shifts in the percentages of several blood T cell subsets (CD3+CD8+, CD4+, CD4+CD25+ and the naive-to-memory ratio). The men did not have gut disease and no symptom score was reported in the abstract, so this is a microbiota finding and not a treatment result.

The gut trials that include coix are of the multi-herb formula Shen Ling Bai Zhu San, so they cannot be attributed to the grain. A meta-analysis of 14 studies with 1,335 participants with chronic gastritis found the formula beat conventional therapy on the effective rate (risk ratio 1.29, 95% CI 1.21 to 1.37), though the authors rate the evidence quality as not high. A network meta-analysis of five Chinese formulas in ulcerative colitis, 64 randomized trials with 5,456 patients, found formulas added to mesalazine did better than mesalazine alone.

What has not been tested: coix as a food in a controlled constipation, diarrhea or bloating trial; any dose-ranging; and the formula with and without coix.

StudyDoseWhat it found
Controlled study in 19 healthy adult men (11 ate coix, 8 had no intervention) PMID 34836336Cooked coix seed 160 g a day for 7 daysHigher intestinal Faecalibacterium abundance and changed blood T cell subset percentages; no symptom outcome reported
Literature review of coix seed as food and medicinal resource PMID 37858750Not applicableLists laboratory and animal effects on microbiota, spleen function and inflammation; calls for clinical trials
Meta-analysis of Shen Ling Bai Zhu San in chronic gastritis: 14 studies, 1,335 participants (ten-herb formula) PMID 36156925Formula; doses not standardizedEffective rate better than conventional therapy, RR 1.29 (95% CI 1.21 to 1.37); evidence quality not high
Network meta-analysis of five formulas added to mesalazine in ulcerative colitis: 64 randomized trials, 5,456 patients (includes Shen Ling Bai Zhu San) PMID 39109018Formulas; add-on to mesalazineTCM plus mesalazine more effective than mesalazine alone

Doses used in trials and traditional preparations

The one human study we found fed 160 g of cooked coix a day for 7 days, which is a food-sized portion of the grain, not a supplement dose. The formula trials used the formula, with the dose of each herb following tradition and, in the review of the formula in colitis, described as unstandardized. We found no extract dose tested for a gut outcome. In the tradition the kernels are decocted with other herbs, simmered in congee, or cooked like barley; we found no single-herb gram dose tied to a primary source.

Treat these figures as a record of what was studied. Whether any amount of coix suits a particular person is a question for a clinician or pharmacist who knows their history.

Safety

Coix is eaten as a grain, and the 7-day study with 160 g a day did not report adverse events in its abstract. TCM sources advise caution in pregnancy, attributing it to a draining action, and we found no controlled pregnancy or breastfeeding data. Stored grains and seeds can carry mold; a survey of 163 commercial edible and medicinal substances in China found fungi in 92% of samples and mycotoxins in 13, with ochratoxin A the most common, though the abstract names a lotus seed sample and not coix as exceeding limits. A published review of Chinese patent medicines in Singapore tabulated excess toxic heavy metals and undeclared drugs reported in some such products from 1990 to 1997, which concerns those products and not coix itself.

Drug interactions

We found no documented drug interaction for coix in the sources read. In laboratory and animal work it has been reported to lower blood sugar, which a review lists among its pharmacological effects, so a person on glucose-lowering medicine is the case a prescriber would think about first; we did not find a human report of a problem. The tradition says coix promotes urination; that is a tradition claim and not a measured effect in the studies we read.

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Related herbs

TCM Chinese yam Dioscorea oppositifolia (also written Dioscorea opposita) TCM Lotus seed Nelumbo nucifera TCM Poria Wolfiporia cocos (syn. Poria cocos) TCM Atractylodes Atractylodes macrocephala (bai zhu); A. lancea (cang zhu)

What people want to know

Is coix the same as pearl barley?

No. Coix is the seed of a different grass. It looks and cooks like pearl barley, which is why it is sold as Chinese pearl barley and Job’s tears, but it is a separate plant.

Has coix been tested for digestion in people?

We found one small study of 19 healthy men in which 11 ate 160 g of cooked coix a day for a week; it measured gut bacteria and blood cells, not symptoms. Gut trials that include coix test the whole Shen Ling Bai Zhu San formula.

What does TCM say about coix?

TCM classes it as sweet, bland and cool, entering the spleen, stomach and lung channels, and uses it for what the texts call dampness with weak spleen, such as loose stools and heaviness. That is the tradition’s framework.

Is it safe in pregnancy?

TCM sources advise caution in pregnancy. We found no controlled pregnancy data for coix.

Sources