Gymnema sylvestre is a woody plant that grows in Southeast Asia and India, where the roots, leaves, and stems have all been used for many years in the ayurvedic system of medicine. In Ayurvedic medicine, GS is used for an array of conditions, including asthma, gastrointestinal complaints, urinary infections, snake bites, and as an antibiotic. Traditionally, it may be used to treat poisoning, abdominal pain, and skin rashes. Its most well-known use, however, has always been as an agent to reduce blood sugar. While Gymnemna sylvestre is still used in Ayurvedic medicine for all of these purposes, its potential to reduce blood sugar has made it a popular supplement in more recent times, where it is often used in people with diabetes, insulin resistance, and metabolic syndrome.^[2]

Gymnema sylvestre supplements may help lower both fasting and postmeal blood sugar levels.^[1][3] This could potentially help people with diabetes improve their sugar control, and could potentially also help prevent people with prediabetic blood sugar levels from progressing to diabetes. GS supplementation may also help lower triglycerides, total cholesterol, and LDL cholesterol levels, which could lower cardiovascular disease risk.^[4][1]

GS could potentially also help with stomach ulcers, as some evidence shows that it improves gastric emptying, raises the pH level of stomach acid and decreases the volume of gastric juices.^[2]

While the effects of GS sound promising, some of these studies have been done only in rats, and some are not of high quality. More randomized clinical trials will need to be done in the future to support these findings.

GS is considered safe at doses of up to 10 g per day; the recommended daily dose of 400 mg is unlikely to produce any toxic effects. Mild side effects, such as diarrhea, stomach cramps, and headache, were reported in one study that used a dosage of 600 mg daily. Whether these effects are dose-related remains unclear.^[1] In some rodent studies, the amount of GS required to be fatal to half the studied rodents (the LD50) has been found to be as high as 3,990 mg of GS per kg of bodyweight (mg/kg).^[2]

However, the safety evaluation of GS is complicated by a number of factors. Different preparations and different parts of the plant itself have different chemical compositions. This makes it difficult to research, as the available supplements are not all the same. Furthermore, toxicology data is limited and not well reported in most of the available studies, and there are very few studies focusing on safety in humans.^[5] Additionally, there are a few case reports of drug-induced liver injury and hepatotoxicity which warrant further investigation.^[6][7]

Hypoglycemia is another potential risk of GS supplementation, since GS is used to lower blood sugars. People with diabetes who are supplementing with GS in addition to their medication should be closely monitoring their blood glucose levels to avoid hypoglycemic episodes.^[5]

It is thought that GS also impacts cytochrome P450, a protein in the liver that is important for drug metabolism. If this is the case, the use of GS could change the absorption, efficacy, and side effects of many different medications, perhaps most notably those used for diabetes treatment.^[5]

GS works to reduce blood glucose through several mechanisms. The phytochemicals found in GS, including gymnemic acid and gymnema saponins, have glucose-lowering properties. GS also blocks intestinal glucose receptors, which lowers the intestinal cells’ absorption of sugars into the blood. It also stimulates the islet cells of the pancreas, which are responsible for insulin production.^[2][4] GS may improve cholesterol levels by increasing pancreatic lipase and increasing fecal excretion of fats.^[4] While studies on rats show that GS may lower some inflammatory markers in the blood, the mechanisms are still unclear.^[8][9][2]

The phytochemical constituents of GS, in particular saponins, sterols, tannins, and triterpenoids, have antiulcer activity. These phytochemicals inhibit the gastric secretion of acid. The extract of GS also decreases the amount of gastric inhibitory peptide release, which is important for gastric emptying rates and nutrient absorption.^[10] GS also contains flavonoids, whose anti-inflammatory effects could be responsible for, or potentiate, its potential antiulcer activity.^[11][2]