Traditionally used for
- Cough & breathing
Cautions & contraindications
- Young children
- Diabetes
- Toxic — professional use only
☯ TCM Properties
Resolves Phlegm, disperses accumulation and swelling and relieves toxicity; Invigorates the Blood and alleviates pain; Suppresses tumors
Traditional Chinese Uses
Mo Yu is the tuber (Rhizoma Amorphophalli) of konjac, Amorphophallus konjac. Pungent, bitter and cold, it resolves Phlegm, disperses accumulations, swellings and nodules, relieves toxicity, invigorates the Blood and stops pain. Traditionally it was used for phlegm masses, goiter and scrofula, and hard swellings; in modern Chinese oncology processed konjac appears in adjuvant formulas for tumors of the breast, liver, lymph and other sites.
Important safety note: the raw tuber is toxic and strongly irritant (owing to its acridity and calcium-oxalate content) and must be thoroughly processed by prolonged cooking/boiling before internal use; it is never taken raw. It is used in decoction or as a prepared gel or flour. Although the record files it under heat-clearing, its core action is phlegm-transforming and mass-dispersing, and it is better understood within that group.
Relationships
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Botanical Description
Amorphophallus konjac (syn. A. rivieri), devil's tongue or konjac, is a tuberous perennial of the Araceae family native to the warm temperate to subtropical forests of central and southern China and Southeast Asia. The plant produces a single very large flattened-globose underground corm that may reach twenty-five centimeters across and several kilograms in weight. From this corm arises a single solitary leaf each season borne on a tall mottled green-and-purple petiole; the leaf blade is highly divided and palmately compound, giving an umbrella-like appearance and capable of reaching over a meter in diameter. In suitable years a striking inflorescence forms instead, with a tall dark-maroon spadix surrounded by a frilled spathe that emits a strong carrion odor to attract carrion-fly pollinators before the foliage emerges.
Active Constituents
Konjac glucomannan
Water-soluble heteropolysaccharide - beta-1,4-linked D-mannose and D-glucose backbone, roughly 1.6:1, carrying acetyl substituentsConcentration: Around 40-60% of the dry corm; refined konjac flour is higher still, and molecular weight and viscosity vary widely between Chinese production regions and between crude and refined powder
The dominant constituent and the reason the drug behaves the way it does. It is the most viscous dietary fibre in commercial use: it hydrates to a gel many times its dry volume, slows gastric emptying, and blunts postprandial glucose and lipid absorption. Meta-analysis of randomised trials attributes lowered total cholesterol, LDL cholesterol, triglycerides, body weight and fasting glucose to it. The same viscosity is the hazard - a gel that forms in the oesophagus or pharynx does not disperse.
Calcium oxalate raphides
Needle-shaped calcium oxalate crystals (idioblast raphides), the araceous acridity principleConcentration: Abundant in the raw corm; largely destroyed or leached by the traditional alkaline-lye and prolonged-boiling preparation
The reason the raw corm is not food and not a drug. Mechanical penetration of oral and pharyngeal mucosa by the crystal needles, together with the co-released irritant proteins typical of the Araceae, causes immediate burning, salivation, oedema and, in severe exposures, airway-threatening swelling; skin contact with the fresh corm blisters. This is the toxicity that the classical instruction to boil the corm for hours in ash-lye exists to remove, and it is why fresh Mo Yu must never be given undecocted.
Starch
Storage polysaccharide (amylose and amylopectin)Concentration: A minor fraction of the corm relative to glucomannan, and largely removed during flour refining
Nutritional bulk with no distinct pharmacology; its removal during refining is what concentrates glucomannan and therefore concentrates both the therapeutic viscosity and the obstruction risk.
Corm protein and free amino acids
ProteinConcentration: A small percentage of the dry corm
Not pharmacologically characterised in this species. Its main relevance is that raw-corm handling reactions in the Araceae are attributed to protein irritants acting alongside the oxalate raphides rather than to the crystals alone.
⚠ Drug Interactions
Sulfonylureas and other oral antidiabetic drugs (glibenclamide, gliclazide, metformin)
Two effects run together. Glucomannan given with a sulfonylurea in man measurably altered the drug's absorption profile, which is the expected consequence of a fibre that raises the viscosity of gastric and small-intestinal contents. Separately, meta-analysis of randomised trials found glucomannan lowered fasting blood glucose by about 7.4 mg/dL on its own. Adding a viscous fibre to a fixed hypoglycaemic regimen therefore changes both how much drug is absorbed and how much glucose lowering the patient needs.
Clinical note: Separate Mo Yu or any glucomannan preparation from oral antidiabetic doses by at least two hours, and warn the patient to monitor capillary glucose more closely for the first fortnight. Do not start it in a patient whose sulfonylurea dose is already producing hypoglycaemic episodes.
Orally administered drugs generally, and narrow-therapeutic-index drugs in particular (levothyroxine, warfarin, digoxin, lithium, antiepileptics)
Konjac glucomannan forms the most viscous solution of any dietary fibre in ordinary use, and viscous fibres slow gastric emptying and impede diffusion of dissolved drug to the mucosal surface. The human sulfonylurea data are the direct demonstration; for other drugs the effect is inferred from the shared mechanism rather than measured. The risk is greatest for drugs whose effect is lost with a modest fall in exposure.
Clinical note: Dose Mo Yu at least two hours away from all regular oral medication. For levothyroxine, warfarin and antiepileptics, check the relevant level or INR two to four weeks after starting or stopping the herb rather than assuming the dose still holds.
Any solid oral dosage form taken with too little water, and drugs that impair swallowing (anticholinergics, sedatives, antipsychotics)
Glucomannan swells on contact with water and, if it hydrates before it clears the oesophagus, forms a plug that does not disperse. Clustered reports of oesophageal obstruction from glucomannan tablets led to regulatory action in Australia and a warning in the BMJ. The same physical property killed children eating konjac jelly mini-cups, which prompted the European Commission in 2002 to suspend the marketing and import of jelly confectionery containing E 425 konjac; jelly mini-cup deaths have also been litigated in East Asian courts. Anything that leaves the gel sitting in the oesophagus - dry swallowing, a supine dose, xerostomia, or drug-induced dysphagia - converts a dietary fibre into an airway hazard.
Clinical note: Never dispense Mo Yu or glucomannan as a dry tablet, capsule or powder to be swallowed as such. Give it fully dispersed in a large volume of water, sitting upright, and not within an hour of lying down. Avoid it altogether in patients with dysphagia, oesophageal stricture, prior obstruction, or on anticholinergic or sedating drugs, and in small children.
Raw or under-processed konjac corm dispensed in place of the prepared drug
Mo Yu is only a medicine after processing. The classical texts specify prolonged boiling in alkaline ash-lye, and modern Chinese materia medica retains a requirement to decoct the drug for two to three hours to reduce toxicity; external application is limited in duration because the fresh corm blisters skin. The acridity is mechanical and chemical injury from oxalate raphides and co-released irritants, not a systemic toxin, so it is not attenuated by dose reduction the way a systemic poison would be - a small amount of raw corm still burns the mouth.
Clinical note: Confirm the batch is processed konjac and specify the long decoction on the prescription. Never authorise a raw-corm powder, a cold infusion, or a tincture of the fresh corm, and keep external applications short and off broken skin.
Fat-soluble vitamins and mineral supplements (iron, zinc, calcium)
A general property of viscous and gel-forming fibres taken chronically at fibre-supplement doses rather than a finding specific to konjac; it has not been demonstrated for Mo Yu at therapeutic TCM doses. It matters most where the herb is taken long term for weight or lipid control rather than as a short course within a phlegm-transforming formula.
Clinical note: For courses beyond a few weeks, take supplements at a different time of day and consider checking ferritin in menstruating women and in anyone with pre-existing deficiency.
Evidence Tier
Strong evidence · 3 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
2
2 verified · 0 unverified
Randomized controlled trial
0
Other clinical trial
0
Observational / case report
1
0 verified · 1 unverified
In vitro / animal
0
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
Effect of glucomannan on plasma lipid and glucose concentrations, body weight, and blood pressure: systematic review and meta-analysis
Meta-analysis of 14 randomised controlled trials (531 participants) of glucomannan, the konjac polysaccharide. Pooled weighted mean differences favoured glucomannan for total cholesterol (-19.28 mg/dL), LDL cholesterol (-15.99 mg/dL), triglycerides (-11.08 mg/dL), body weight (-0.79 kg) and fasting blood glucose (-7.44 mg/dL); HDL cholesterol and blood pressure were unchanged. Children, patients already receiving dietary modification and patients with impaired glucose metabolism benefited less. This is the strongest human evidence for the constituent, and it is evidence about purified glucomannan rather than about a decoction of the corm.
The effect of glucomannan on body weight in overweight or obese children and adults: A systematic review of randomized controlled trials
Systematic review of randomised trials of glucomannan for weight reduction, deliberately separating paediatric from adult data. It is the more sceptical counterweight to the earlier lipid meta-analysis: the weight-loss signal is small and the trials are short and heterogeneous. Cited here so the record does not overstate what the fibre does at doses a patient can actually tolerate.
Effect of Dietary Fiber, Glucomannan, on Absorption of Sulfonylurea in Man
Controlled human study of glucomannan taken with a sulfonylurea, showing an altered absorption profile for the drug. Small and old, but it is the direct human demonstration behind the whole class of viscous-fibre absorption interactions, and the drug class involved is one that Mo Yu's own glucose-lowering effect also acts on.
Historical Texts
Kai Bao Ben Cao (Materia Medica of the Kaibao Era)
Northern Song dynasty, 973-974 CEBen Cao Gang Mu (Compendium of Materia Medica), Li Shizhen
Ming dynasty, 1596Ben Cao Gang Mu Shi Yi (Supplement to the Compendium of Materia Medica), Zhao Xuemin
Qing dynasty, 1765References
- Henry D A, Mitchell A S, Aylward J, Fung M T, McEwen J, Rohan A. Glucomannan and risk of oesophageal obstruction. . BMJ (1986) [DOI]
- Kim Suk Shin. The Mini-Cup Jelly Court Cases: A Comparative Analysis from a Food Ethics Perspective . Journal of Agricultural and Environmental Ethics (2014) [DOI]
- European Commission. 2002/247/EC: Commission Decision of 27 March 2002 suspending the placing on the market and import of jelly confectionery containing the food additive E 425 konjac . Official Journal of the European Communities (2002)
- Fang Weixuan, Wu Pengwu. Variations of Konjac glucomannan (KGM) from Amorphophallus konjac and its refined powder in China . Food Hydrocolloids (2004) [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.
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