Glucomannan Side Effects | Risks & Warnings

Shop around for fat burners and weight loss supplements and you will quickly notice glucomannan comes up quite regularly. In fact, by weight alone, it is often the largest component ingredient in many of the supplements that use it. 

Apart from weight loss, glucomannan is thought to have a number of health benefits such as cholesterol reduction, blood glucose regulation, constipation relief and general gastrointestinal health. But despite its benefits, it is not devoid of downsides. Though rare, glucomannan can have significant side effects you need to take note of before you start using it.

Main Takeaways

  • Glucomannan has proven to be a potent weapon in the management of cholesterol, blood glucose and weight.
  • Studies have identified rare side effects though the majority are deemed mild. Choking on glucomannan tablets does seem to be the most severe adverse effect.
  • Applying recommended paths of safe glucomannan consumption can substantially reduce the risk of side effects.

What is Glucomannan

Glucomannan is a fiber derived from the konjac plant. It has been a fixture of Eastern medicine for millennia though it has only come to the fore in the West over the last four or so decades. Today, you will find glucomannan in numerous weight management supplements. 

Its primary strength is not just that it is water soluble but that it is the most viscous dietary fiber currently known. So extraordinary that glucomannan absorbs as much as 50 times its weight in water. It balloons in size when in the digestive tract creating a sense of fullness and reducing food cravings.

Research-Backed Side Effects

There are multiple studies exploring glucomannan various health benefits. It is within these studies that adverse effects have been reported. As glucomannan is primarily used in weight management, many of the known side effects relate to gastrointestinal problems.


Glucomannan’s greatest asset is also the source of one of its drawbacks. As contact with water forms an expanding gel, the feeling of satiety could, in rare instances, give way to bloating and meteorism. 

In a 1990 study evaluating the impact of glucomannan in patients undergoing cardiac rehabilitation, some subjects on glucomannan did report a decline in weight and cholesterol but also complained of mild meteorism (i.e. bloating).

Abdominal Pain and Discomfort

Glucomannan ingestion may cause stomach pain and discomfort, even though this occurs relatively rarely. In 1989, researchers published a study that looked at the effect of glucomannan treatment on overweight patients grappling with osteoporosis. Some participants in the glucomannan group reported abdominal discomfort.

This side effect was corroborated in a 2006 clinical trial published in the European Journal of Clinical Nutrition. Glucomannan supplementation was associated with notable abdominal discomfort.

Flatulence and Soft Stool

We have already noted that glucomannan causes bloating so flatulence as a mild, occasional side effect is not unexpected. But glucomannan may also, rarely, cause soft stool. In a 2000 clinical trial published in the Diabetes Care journal, some study participants on glucomannan experienced increased flatulence and soft stools.

Diarrhea and Constipation

You are probably wondering what is the difference between soft stool and diarrhea. If you experience at least three instances of soft stool in one day, you are considered to have diarrhea. Glucomannan may cause diarrhea but, somewhat counterintuitively, has also been reported to trigger constipation though both of these side effects are uncommon in current studies.

In 2007, scientists published a clinical trial in the Metabolism Clinical and Experimental journal. Some of the study subjects placed on glucomannan reported diarrhea and constipation.


Thanks to glucomannan’s exceptional capacity to absorb large quantities of water, taking the supplement can result in choking and other gastrointestinal obstruction in very rare circumstances. And the risk is higher when glucomannan is taken in tablet form and downed with little to no water. There are hardly any reports of choking when the supplement is taken in capsule or powder form.

In Australia, seven cases of esophageal obstruction were reported between 1984 and 1985. A few choking incidents associated with glucomannan tablets have also been reported in other countries. As a result, production and/or marketing glucomannan tablets is prohibited in Australia and several other jurisdictions.

In the US, the FDA has cautioned on the use of glucomannan in candies imported from Asia after six deaths among children in the US and Asia caused by choking. This led to the recall of multiple imported konjac candy brands.

Inhibiting Drug Absorption

Glucomannan’s use in weight management and cholesterol reduction is to a large extent due to its ability to suppress nutrient absorption. It is suspected that this capability may, in exceptional circumstances, have unintended consequences — glucomannan supplementation can inhibit the absorption of certain medications.

Some limited studies suggest glucomannan can interfere with antidiabetic, antihypertensive, antiobesity, antilipemics and thyroid medications.

Safe Consumption of Glucomannan

You can reduce the risk of experiencing adverse effects by applying the following measures:

Take only as much glucomannan as you need. Studies indicate anything from 1,000 mg to 3,000 mg (1 to 3 grams) per day is ideal. If it’s your first time taking glucomannan, start off with the lowest possible dosage then gradually increase while monitoring for adverse effects.

Avoid glucomannan tablets even where they are not prohibited. Instead, opt for supplements that come in powder or capsule form as these are deemed considerably safer with lower risk of choking.

Irrespective of the form you take glucomannan supplements, it should be accompanied by plenty of water or other liquid to wash it down fast. Health Canada recommends at least 240 ml of liquid.

If you are on any medication, allow a multi-hour gap between when you take the drugs and when you ingest the glucomannan supplement.


Glucomannan’s popularity as a dietary supplement is not without merit. Research backs up many of the claims around it, especially its ability to reduce bad cholesterol and suppress appetite. 

But it’s not all good news. Glucomannan is plagued by several adverse effects including more serious ones such as gastrointestinal obstruction. While these side effects are rare and the severity may vary widely between individuals, it’s important to know them and take appropriate steps to mitigate the risks. When in doubt, consult your doctor.

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About the Author

Sam is a passionate health and fitness enthusiast who has been interested in supplements, fitness, and wellness for over 10 years. He is the founder of Great Green Wall - the health and wellness brand and has completed multiple fitness certificates, including personal training and nutrition certifications. Sam has been working as a personal trainer for the past three years and is dedicated to helping his clients achieve their fitness goals and lead healthier lifestyles. He believes that a healthy lifestyle is crucial to a happy and fulfilling life and is committed to sharing his knowledge and passion with others.

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