Herbs to Avoid on Metformin

Metformin is usually prescribed for Type 2 diabetes patients who have trouble maintaining consistent blood sugar levels. As a general rule, it is unsafe to take any herbs, supplements or vitamins while taking metformin unless you have the express approval of your doctor. Many of these over-the-counter substances can lower your blood sugar too much or make the metformin less effective in controlling your blood sugar. Before taking any herbs with this medication, talk to your doctor and pharmacist to ensure safety.

Many herbs interact with the prescription drug metformin. Credit: sufnifoto/iStock/Getty Images


Metformin is a type of antidiabetic drug called a biguanide. Credit: Jaykayl/iStock/Getty Images

Metformin is a type of antidiabetic drug called a biguanide. It is used primarily to lower blood sugar in Type 2 diabetics, but it is also used to treat the side effects of polycystic ovarian syndrome and nonalcoholic fatty liver disease. Some side effects include headache, muscle pain, weakness, mild nausea, vomiting, gas and diarrhea. Take this medication with a meal to avoid some of these side effects, and you should take vitamin B-12 to avoid the deficiency metformin can sometimes cause.

Herbs to Avoid

Avoid herbs like aloe and ginseng. Credit: ChViroj/iStock/Getty Images

Some supplements and herbs lower your blood sugar and can make it drop too low when you're taking metformin. Herbs and supplements in this category include ipriflavone, chromium, ginseng, magnesium, vanadium, aloe, bitter melon, bilberry, burdock, dandelion, fenugreek, garlic, gymnema, lipoic acid and carmitine. St. John's wort and Dong quai can increase the sun sensitivity caused by metformin. Guar gum can interfere with the medication's absorption, and gingko biloba combined with metformin made glucose tolerance worse in patients -- their blood sugars remained higher with the combination.

Other Drug Interactions

Metformin also interacts with many prescription drugs. Credit: Fuse/Fuse/Getty Images

Metformin interacts with many prescription drugs, as well. Tell you doctor if you take the water pill Lasix, the heart medication digoxin or the antibiotic vancomycin. Other medications to mention include nifedipine, cimetidine, amiloride and morphine. Some medications can cause a higher blood sugar than normal and interact with metformin. These medication types include water pills, steroids, some heart and blood pressure medications, niacin, birth control pills, seizure medicines, diet pills, cold pills and medicine to treat allergies.

Other Safety Considerations

Watch out for early warning signs of lactic acidosis. Credit: Wavebreakmedia Ltd/Wavebreak Media/Getty Images

The major safety concern with metformin is a rare but serious side effect known as lactic acidosis. This happens when lactic acid builds up in the muscles, and it can be fatal. Some early warning signs are muscle pain, weakness, numb or cold feeling in arms and legs, difficulty breathing, dizziness, stomach pain, nausea with vomiting, and a slow, irregular heartbeat. This condition is a medical emergency, so call your doctor even if you have minor symptoms of lactic acidosis.

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