Metformin (Glucophage, Glumetza, Fortamet) is typically prescribed to counteract the effects of insulin resistance -- the body's sluggish response to the blood-sugar-lowering hormone insulin. Insulin resistance can lead to high blood sugars and may eventually progress to prediabetes or type 2 diabetes (T2DM). Metformin improves insulin sensitivity of the body tissues and reduces liver glucose production, both of which help lower blood sugar levels. The American Diabetes Association recommends metformin as a first-choice medicine to treat T2DM. It is also sometimes used in combination with exercise and weight loss in people with prediabetes. Some evidence suggests that a few herbs might mimic some of the effects of metformin. However, no herb is a proven alternative to metformin.
Goat’s rue, or Galega officinalis, is an age-old remedy. In times past, it was used for assorted ailments, including diabetes. Metformin is a man-made chemical that's closely related to a substance found in goat’s rue. Animal studies from the 1970s and 1980s established that substances in goat's rue have blood-sugar-lowering effects. Some of these chemicals can be toxic, however, so human studies are lacking. A recent animal study was published in April 2008 in the "British Journal of Pharmacology." Researchers found that mice fed galegine -- a chemical found in goat's rue -- ate less, lost weight and had reduced blood sugar levels, compared to mice that weren't fed the chemical.
Goat's rue is not approved for diabetes treatment by the U.S. Food and Drug Administration or Germany's Commission E, a scientific advisory board that reviews and approves herbal medicines. Commission E noted significant health risks with goat's rue and the availability of more effective diabetes treatments. Importantly, animal studies show that goat's rue may be harmful during pregnancy.
Bitter melon has long been used as a folk remedy for diabetes. Several substances found in the fruit and seeds of bitter melon reportedly have blood-sugar-lowering effects. However, research on the effectiveness of bitter melon as a diabetes remedy has been mixed. A February 2002 "Alternative Medicine Review" article reported that 2 small studies conducted in people with diabetes suggested blood-sugar-lowering effects. However, a December 2014 "Nutrition and Diabetes" article that analyzed results from 4 studies reported that people with T2DM experienced no significant reduction in blood sugar, compared to people taking an inactive substance. Bitter melon is not approved for diabetes treatment by the FDA. Animal studies indicate bitter melon may reduce fertility and increase the risk for miscarriage.
Berberine is a potentially powerful chemical derived from different plants, including goldenseal, goldenthread and tree turmeric. This herbal remedy has been used in traditional Chinese medicine to treat various conditions, including diabetes. An October 2012 "Evidence-Based Complementary and Alternative Medicine" article reported on the pooled results from 14 studies examining berberine for T2DM treatment. The researchers found that berberine plus diet and exercise led to lower blood sugar levels than diet and exercise alone. They also noted evidence that adding berberine to oral diabetes medicines leads to lower blood sugars than oral diabetes medicines alone. The researchers cautioned, however, that the quality of the studies was generally poor, which could lead to inaccurate conclusions.
Large, well-designed studies are needed to determine whether berberine may be useful for diabetes treatment. It is not FDA-approved for diabetes treatment as of 2016. Large doses of berberine may cause digestive system upset, flulike symptoms, shortness of breath and low blood pressure. It may also increase the risk for miscarriage by stimulating uterine contractions.
Cinnamon has also been suggested as a possible herbal treatment for diabetes. A September 2013 "Annals of Family Medicine" article examined the pooled results from 10 studies wherein 543 people with T2DM took daily cinnamon or an inactive placebo for 4 to 18 weeks. Many study participants also took oral diabetes medicines. The researchers found that participants taking cinnamon had lower fasting blood sugar levels than those taking a placebo. However, there was no effect on A1C, a test to measure long-term blood sugar control. The researchers cautioned that insufficient research has been performed to apply these findings to routine diabetes treatment. More research is also needed to determine dosing amounts, the best form of cinnamon to use and to clarify for whom this herbal remedy might be useful.
As of 2016, cinnamon is not FDA-approved for diabetes treatment. While cinnamon is generally safe, animal studies indicate that large doses may trigger liver inflammation and reduced clotting ability. Safety studies for pregnant and breastfeeding women are lacking.
No herb has been proved a safe and effective alternative to metformin. You should never change the dosage or stop taking metformin without first consulting your doctor. Stopping or reducing diabetes medications could lead to high blood sugar levels that could be life-threatening. It's also important not to start taking herbs in combination with your diabetes medicines without discussing it with your doctor, as dangerously low blood sugar levels could occur. Herbal supplements could also interact with other medications you're taking, making them less effective or more toxic.