Glucomannan (Amorphophallus konjac)

Water-soluble dietary fibre from konjac root (Amorphophallus konjac); the only weight-loss supplement with an EFSA-approved health claim under Regulation 432/2012

ATC code: A08AX-GLUCOMANNAN

Brand names: NOW Glucomannan, Konjac fibre (various), Lipozene

Updated 24 Sep 2026 · Methodology

Indications

Weight loss

Adjunct

Glucomannan is the only weight-loss supplement with an -approved health claim under Regulation (EU) 432/2012. The approval terms are explicit: 3 g/day (1 g three times daily) with a large glass of water 15–30 minutes before meals, within a calorie-restricted diet. The Onakpoya 2014 meta-analysis reported average weight loss of 0.79 kg over 5 weeks vs placebo – modest but statistically significant. Glucomannan is not a «fat burner» but a tool for portion control and satiety. Without a caloric deficit and physical activity it does not work. Patients with constipation tendency or those whose other medications can be slowed should discuss use with a gastroenterologist or general practitioner.

Sources

Chronic constipation

Adjunct

On iHerb and marketplaces glucomannan is often sold «for constipation» as a natural laxative. has not approved a separate bowel-function health claim – outside the weight-loss indication this is off-label use. Glucomannan increases stool bulk by retaining water, similar in theory to other soluble fibres, but quality RCTs with stool-frequency endpoints are sparse. In some patients concentrated glucomannan worsens constipation and causes bloating. 2024 and SEPD recommend dietary fibre, adequate fluids and physical activity for chronic constipation, with macrogol, lactulose or prucalopride as needed by physician prescription.

Sources

EFSA: Scientific opinion on glucomannan – cholesterol and blood glucose claims (2009)

ICD-10: K59.0 · ICD-11: ME05.0

Marketing claims without evidence base

The drug is promoted for these uses outside international guidelines. Each entry below is analyzed against AEMPS, FDA, EMA, Cochrane and major RCTs.

Dyslipidemia

Not recommended

Glucomannan marketing often pushes «cholesterol and blood sugar» claims. explicitly rejected the broader health claim in 2009 – only the weight-loss indication is approved. Meta-analyses in hypercholesterolaemia show a weak reduction in total and cholesterol of about 10–15 mg/dL, far less than statins and fibrates. and SEC treat dyslipidaemia with lifestyle change and statins as indicated, not supplements. Raised cholesterol or LDL on the lipid panel requires in-person evaluation and risk stratification with , not a pharmacy glucomannan course.

Sources

ICD-10: E78 · ICD-11: 5C80

How to read tiers A–F

AStrong evidence – first or second line in international guidelines
BRecommended in selected cases
CStudy data contradict each other
DBenefit not proven, no documented harm
FDocumented harm, or risk without benefit

Mechanism of action

Polysaccharide of D-mannose and D-glucose units in roughly 1.6:1 ratio linked by β-1,4 glycosidic bonds. In the stomach it swells 50–200 times: 1 g of powder binds 50–100 mL of water and forms a viscous gel. The gel stretches the gastric wall, activates satiety receptors and slows gastric emptying. In the small intestine the viscous gel slows glucose and bile acid absorption. It is fully fermented in the colon to short-chain fatty acids. Calorific value is close to 0 kcal/g.

Safety

Contraindications

Oesophageal stenosis, achalasia and gastrointestinal strictures
Severe dysphagia
History of acute intestinal obstruction
Age under 18 years (concentrated glucomannan)
Concurrent oral medication intake (risk of slowed absorption)

Serious adverse effects

Oesophageal obstruction and asphyxia when capsule or powder is swallowed without enough water
Acute intestinal obstruction in patients with strictures and adhesions
Reduced absorption of oral medications: oral contraceptives, levothyroxine, warfarin, digoxin

Common adverse effects

Flatulence and bloating
Sensation of gastric fullness
Loose stools or, conversely, constipation with inadequate fluid intake
Belching

Pregnancy: can you take Glucomannan (Amorphophallus konjac)?

Not absorbed systemically. AESAN permits dietary fibres in pregnancy at normal food doses. Concentrated glucomannan supplements for weight loss are not indicated in pregnancy – caloric deficit harms the fetus.

Breastfeeding: can you take Glucomannan (Amorphophallus konjac)?

Compatible at food doses. Not absorbed systemically and not present in milk. Weight-loss intake during lactation is not justified – adequate caloric intake supports milk supply.

Calculate RID

Reference information, not a clinical decision. Discuss feeding pauses or changes with your physician or an IBCLC.

Check interaction with another drug

Opens the checker prefilled with this drug. Pick the second one from your regimen.

Open checker

Summary of a multi-drug list →

Medicine list: everything you take in one place →

Frequently asked

What is Glucomannan (Amorphophallus konjac) used for?

Glucomannan (Amorphophallus konjac) is evaluated for the following indications with varying evidence strength: Weight loss (evidence tier B), Dyslipidemia (evidence tier D), Chronic constipation (evidence tier D). See the full indication matrix with dosing and citations above on this page.

What are the side effects of Glucomannan (Amorphophallus konjac)?

Common side effects of Glucomannan (Amorphophallus konjac) (≥ 1 in 100): Flatulence and bloating, Sensation of gastric fullness, Loose stools or, conversely, constipation with inadequate fluid intake, Belching. See the Safety section for uncommon and serious reactions.

Is Glucomannan (Amorphophallus konjac) safe during pregnancy?

Is Glucomannan (Amorphophallus konjac) compatible with breastfeeding?

Compatible at food doses. Not absorbed systemically and not present in milk. Weight-loss intake during lactation is not justified – adequate caloric intake supports milk supply.

Who should not take Glucomannan (Amorphophallus konjac)?

Glucomannan (Amorphophallus konjac) is contraindicated in: Oesophageal stenosis, achalasia and gastrointestinal strictures; Severe dysphagia; History of acute intestinal obstruction; Age under 18 years (concentrated glucomannan); Concurrent oral medication intake (risk of slowed absorption). Full list in the Safety section.

Other drugs in this group

Conjugated linoleic acid (CLA), Garcinia cambogia (hydroxycitric acid, HCA), Orlistat