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Side Effects — Good, Bad, and Neutral
Metformin’s job is to lower your blood glucose. But like all complex and imperfectly understood drugs, it has some side effects.
STOMACH IRRITATION, DIARRHEA
Causes. Not fully established. The leading theory is that metformin slows the rate of bile salt reabsorption in the intestines, which in turn could disturb the activity of bacteria in the colon.
Solution. Start low and go slow. When starting metformin, most people do well with starting with 500 mg at night or with dinner, and staying at this dose for a full week. At that point, a second 500-mg pill can be added in the morning. After another week, a third pill can be added to the evening dose. After one more week, a fourth pill can be added to the morning dose, so that by the end of the month, the full daily dose of 2,000 mg is being taken.
People who experience chronic irritation on a full dose may still benefit from a partial dose of metformin, and people with chronic irritation who started on a full dose can sometimes eliminate this irritation by cutting back and slowly building back up to a full dose.
Alternate solution. Switch to the extended-release (XR) version of metformin, which is tolerated better by most people.
Causes. Not entirely clear, but the leading theories are that metformin reduces oxidative stress, reduces hardening of the arteries, improves endothelial function (functioning of cells lining the blood vessels), or any combination of the above.
Solution. None needed, other than continuing to take metformin, even as other drugs are added to your diabetes control regimen.
CONTRAST DYE ISSUES
Why. Metformin is cleared from the body by the kidneys, as are contrast dyes. When the two are combined, they carry a theoretical risk of kidney damage from overload. In addition, toxic levels of metformin can build up in the blood due to short-term reduced kidney function from the contrast dye, increasing the risk of lactic acidosis (an emergency situation in which the blood becomes acidic).
Solution. Stop taking metformin either before or at the time of the imaging study, and take no doses for at least 48 hours afterward, while the contrast dye is being cleared from the bloodstream.
VITAMIN B12 DEFICIENCY
Solution. Studies to investigate how much B12 supplementation is needed are ongoing. For the time being, some doctors recommend an annual B12 shot, while others prefer monthly oral supplements.
APPEARANCE OF INTACT CAPSULE IN STOOL
Causes. It’s unknown why the shell is digested in some people but not in others.
Solution. Ignore it.
INCREASED FERTILITY IN WOMEN
Solution. Start or continue birth-control measures, or plan a visit to the maternity ward.
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