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More Americans than ever are taking prescription drugs — close to 60 percent of U.S. adults, according to new research.

And most seem to be related to obesity, with cholesterol and blood pressure drugs leading the pack, researchers report in the Journal of the American Medical Association.

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The single most popular drug is Zocor, a cholesterol-lowering drug in a class called statins, said Elizabeth Kantor, formerly of the Harvard T.H. Chan School of Public Health in Boston, and now at Memorial Sloan Kettering Cancer Center in New York. The drug, known generically as simvastatin, is taken by 8 percent of the U.S. population.

Robert Granville reaches into a medicine bottle as he takes his seven prescription pills on February 25, 2009 in Miami, Florida. Joe Raedle / Getty Images

Her team used national surveys of more than 37,000 adults to find that the percentage of people taking prescription drugs rose from 51 percent of the adult population in 1999 to 59 percent in 2011.

The population is getting older, but that doesn’t explain it, Kantor said. The pattern looks more related to obesity, which is steadily rising, More than two-thirds of the adult U.S. population is overweight or obese, and many suffer the heart disease, diabetes and other metabolic disorders that go along with being too heavy.

And more people are taking five or more drugs at once. In 1999, 8.2 percent of adults did. In 2011, 15 percent of adults did. “This is particularly notable among older adults 65 and older,” Kantor said. That’s 39 percent of the age group.

More people are also taking antidepressants and proton pump inhibitors, used to treat acid reflux disease, Kantor's team found. Acid reflux can be related to obesity and poor diet.

One type of prescription drug use fell. Fewer women take hormones to treat the symptoms of menopause, mostly because of studies indicating the hormone pills could raise the risk of breast cancer and other diseases.