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Side Effects of Metformin 500 mg Tablets

author image A.M. Tacon
A.M. Tacon is an associate professor of health at Texas Tech University. Her research interests include psychosocial factors in cancer, complementary therapies and stress reduction in individuals with cancer. Dr. Tacon runs mindfulness-based stress reduction programs for women with breast cancer, which is based on various forms of mindfulness meditation.
Side Effects of Metformin 500 mg Tablets
Metformin is a drug designed to treat type 2 diabetes. Photo Credit Jupiterimages/Polka Dot/Getty Images

Metformin HCL 500 mg is an oral prescription medication used to treat type 2 diabetes. It is sold under such brand names as Glucophage, Fortamet, and Riomet, and belongs to a drug group known as biguanides. Metformin controls the amount of glucose or blood sugar in the body by several actions including decreasing the amount of glucose produced by the liver, decreasing the amount of glucose absorbed by the intestines and enhancing the body's ability to use insulin more efficiently. It can, however, produce adverse effects.

Diarrhea and Nausea

A common reaction to beginning this medication is digestive or gastrointestinal upset. Diarrhea, according to eMedTv, occurred in up to 53.2 percent of the participants taking this drug during clinical trials. Additionally, nausea and vomiting were experienced by up to 25.5 percent of clinical trial participants, along with other symptoms such as excess gas and bloating--up to 12 percent of participants, indigestion--up to 7.1 percent, or stomach pain--up to 6.4 percent. These temporary side effects usually occur at the beginning of metformin therapy and disappear as the body becomes adjusted to the medication.

Lactic Acidosis

According to the Diabetes Monitor, lactic acidosis is a rare yet serious side effect of Metformin that occurs in 1 in 33,000 people who take this medication for approximately one year. Lactic acidosis occurs when lactic acid accumulates in the body, which results in high levels in the bloodstream. While it has a low incidence rate, lactic acidosis is life-threatening; that is, it is fatal in nearly half the people who develop this complication. Lactic acidosis can produce secondary symptoms such as a breathing problems, dizziness, irregular heartbeat and severe weakness. Emergency medical treatment may become necessary should a variety of these symptoms present.


Since Metformin's function is to reduce high levels of blood sugar, it has the potential to lower glucose below what is considered the normal levels. This produces the side effect known as hypoglycemia, or low concentrations of glucose in the bloodstream. Some signs and symptoms of low blood sugar include: weakness, dizziness, shaking and sweating. In a situation in which a patient feels some or all these symptoms, they must raise the blood sugar immediately to avoid complications such as coma. Therefore, patients need to always have available hard candy or natural juice to counter this side effect.

Renal and Liver Impairment

Metformin is excreted from the body through the kidneys, therefore, those with renal disease may experience a build-up of this drug due to renal impairment. Also, this drug may produce adverse reactions in those with liver impairment. Both conditions have the potential to produce lactic acidosis. Therefore, individuals with a history of kidney or liver disease may not be good candidates for Metformin therapy, which makes it essential that one supplies the prescribing physician with as accurate a medical history as possible.

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