Scientists and doctors aren't certain of all the possible burdock side effects, nor of how often patients may experience these effects because only been limited medical studies have been done on burdock, and most of them have been conducted on animals. Anecdotal evidence has, however, revealed a number of common side effects that patients may experience when using this plant as an herbal supplement. Most patients will not experience any uncomfortable effects from the use of this herb, and burdock may also be eaten as a prepared food, in which case there are no known side effects.
Burdock is used to draw fluid out of the body. As a side effect, most patients experience an increase in the amount of urine, and taking burdock for a long time or at a high dose can lead to dehydration. Patients can reduce the risk of becoming dehydrated by drinking extra water while taking burdock.
Patients may also experience burdock side effects that interfere with blood sugar levels. The use of this herbal supplement may lower blood sugar levels temporarily, and patients with trouble regulating blood sugar, such as diabetics, may experience severe fluctuations in blood sugar, which could endanger their health. These potential side effects have not been well studied, however, and scientists are not certain that burdock can affect blood sugar levels in humans.
Burdock contains a great deal of tannin, and if enough of the plant is consumed, these tannins can cause gastrointestinal discomfort. Consuming high levels of tannin can be toxic, leading to damage of the liver or kidneys, but there does not appear to be enough present in burdock to harm a human patient. Over time, high concentrations of tannin can also increase a patient's risk of developing certain types of cancer, though it is not known if these cancers should be considered possible burdock side effects.
Occasionally, patients who take burdock may notice a slowing of the heart rate. Though this is not believed to be one of the burdock side effects, it is sometimes seen in patients who take burdock when a similar looking plant, belladonna, has contaminated the herb. Belladonna, which can cause dry mouth, is an extremely toxic plant and can cause death in high enough doses. Patients should exercise caution when choosing a burdock supplement to take and should choose supplements created by reputable companies because of the risk of contamination from this plant.