Worms given an antidepressant lived 31 percent longer than average, a life span increase that translates to about 24 human years, a study found.

The antidepressant, called mianserin, may have helped the worms, a type of roundworm called c. elegans, live longer by sparking deep-seated survival mechanisms, the researchers said. The study, by scientists from the Howard Hughes Medical Institute's Basic Sciences Division in Seattle, is published in the science journal Nature.

Scientists tested 88,000 chemicals for the ability to extend the lifespan of the worms, which is about three weeks, before zeroing in on mianserin. The drug may cause the body to think it's starving even with adequate food intake, which would activate the same survival mechanisms as a calorie-restricted diet, the authors wrote.

One side-effect of mianserin in humans is increased appetite, they said.

"We don't have an explanation for this," head researcher Linda Buck said in a statement distributed by Howard Hughes Medical Institute. "All we can say is that if we give the drug to caloric-restricted animals, it doesn't increase their lifespan any further. That suggests the same mechanism may be involved."

Mianserin, from a class of medicines called tetracyclics, increases serotonin in humans, researchers said. The brain chemical serotonin regulates appetite as well as mood. Researchers also tested three other chemical compounds that extended the worms' lifespan by 20 to 33 percent. All three also affect serotonin in humans.

The c. elegans worm is commonly used in scientific research because it has a life cycle that is similar to, though shorter than, humans. In 2002, Sydney Brenner, H. Robert Horvitz and John Sulston won the Nobel Prize for Medicine for their work on programmed cell death and organ development in these animals. In 2006, Andrew Fire and Craig C. Mello won for demonstrating in the worms how organisms control the flow of genetic information.