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Metformin Side Effects & Weight Loss

author image Karla Casco
Karla Casco began writing in 2010, focusing her work on diseases and treatments and their side effects. She has also created patient handouts, PowerPoint presentations and journal clubs. Karla has a doctorate in pharmacy from St. John's University and holds a pharmacy license for the state of New York.
Metformin Side Effects & Weight Loss
Predcription medication pills in a hand. Photo Credit: miflippo/iStock/Getty Images

Metformin is the only prescription medication that is classified as a biguanide. It is used for the management of type 2 diabetes when high blood sugar levels are inadequately controlled by diet and exercise. It may be used along with other antidiabetic medications, such as insulin or glyburide. Metformin decreases the amount of glucose, or sugar, produced by the liver to lower levels in the body. It also leads to a decreased absorption of glucose from the intestines. Furthermore, the drug increases sensitivity to insulin, allowing the body to use it more effectively. Many side effects may occur with the use of this medication.

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Nausea, Vomiting, Diarrhea

The most frequent side effects of metformin are gastrointestinal. Nausea and vomiting may occur in 7 to 26 percent of individuals, according to The Merck Manuals Online Medical Library. Diarrhea may be seen in up to 53 percent of patients. Abdominal pain and indigestion may also occur in about 6 percent of patients. These side effects are temporary and lessen over several weeks. You should take metformin with meals to avoid these adverse reactions. Chewing gum may also alleviate nausea and stomach pain. The extended release form of metformin causes less gastrointestinal side effects than the immediate release. You should speak with a physician if you experience these side effects and discuss the option of switching to the extended release drug or reducing the dose.

Vitamin B12 Deficiency

Metformin may reduce the absorption of vitamin B12 and annual screening of its levels is recommended, according to “Basic and Clinical Pharmacology.” About 7 percent of individuals may experience a reduced level of vitamin B12. A physician can monitor B12 levels and determine if the need for vitamin B12 injections.

Headache and Dizziness

Headaches are common side effects that may occur in about 6 percent of individuals, reports the “Drug Information Handbook.” Metformin may also lead to dizziness and lightheadedness in about 5 percent of patients. Weakness may be present in up to 9 percent of individuals. Use caution while driving or performing activities that require alertness until you know how the drug affects your body. If these side effects become severe or are accompanied by a fever, contact a physician.

Weight Loss

Weight loss may be seen in patients when the drug is started. “Pharmacotherapy: A Pathophysiologic Approach,” explains that metformin causes a loss of appetite and feelings of fullness and leads to weight loss. If you are following a restricted diet and exercising regularly, you may see a significant reduction in weight. Weight loss is desired in diabetic patients to help control glucose levels and improve insulin resistance.

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