Listen to any TV commercial for a new drug and you'll hear a litany of bizarre side effects — amnesia, hallucinations, nightmares, blue urine and a furry-feeling tongue, just to name a few. But few of these lists include obesity, and overdosing on antibiotics, according to an article published in the magazine New Scientist, could be a major trigger for obesity.

People who overuse antibiotics have lower levels of good bacteria in their guts, and those good bacteria have been found to help prevent everything from cancer to obesity. A number of studies on mice have found that mice fed antibiotics at levels comparable to those given to farm animals are much heavier than mice fed no antibiotics at all — which isn't surprising, considering that antibiotics are often used to speed growth and fatten up animals for slaughter.

But what is concerning are the studies of antibiotics fed to mice at levels similar to what children receive when they get infections. In one study, microbiologist Martin Blaser, of New York University, fed mice short courses of antibiotics similar to those that children receive. Compared to the non-drugged mice, the antibiotic-fed mice had lower levels of T-cells, which regulate the body's immune response. Obesity has been associated with low levels of these T-cells.

In a separate observational study, published in the April 2011 issue of the International Journal of Obesity, researchers from Denmark followed the development of 28,000 babies, and for seven years, monitored the children's weight and development. Babies who were given antibiotics within six months of birth were more likely to be overweight by age 7 than children who hadn't received such early doses of the drugs, regardless of how trim or obese their mothers were.

All these studies are too preliminary, the authors write, to suggest that use of the antibiotics be stopped altogether, but they do advise that the drugs be used more prudently. Often, people go to the doctor expecting to receive antibiotics to treat a condition, even if antibiotics won't do anything to treat that problem, such as asking for antibiotics to treat sinus infections, which are often caused by a virus, not bacteria.

For more on whether you really need antibiotics to treat an illness, see "Do You Really Need That Antibiotic?" and "New Rule: Don't Take Antibiotics for This Common Condition." In the meantime, eat organic! Antibiotics are prohibited in organic animal husbandry, and if all those drugs are fattening up animals, it can't be good for your waistline to eat drugged-up beef and chicken.

Story by Emily Main. This article is reprinted with permission from

Are antibiotics making you fat?
Discover more about why you should avoid certain antibiotic-laden foods and not always rely on them to treat illness.