In a dramatic decrease from 2000, almost three out of five Americans take prescription drugs for conditions from depression, to high cholesterol, and diabetes.

The Washington Post reports that a study released Tuesday in the Journal of the American Medical Association found that prescription drug use by adults 20 years old and up rose from 51 percent to 59 percent, in about twelve years. The percentage of individuals who take five or more prescriptions a day almost doubled, up from eight percent to 15 percent.

Obesity is considered a likely cause for the increase in prescription use. Eight out of ten of the most prescribed prescriptions deal with health issues with direct ties to obesity, such as hypertension, diabetes, and gastroesophageal reflux.

A co-author of the study and epidemiologist Elizabeth Kantor urged individuals to not draw quick conclusions from the data. Researchers are not sure exactly why there is an increase in prescription drug use, and that individual reasons likely vary from drug to drug. New drugs are prescribed, others become no longer protected by patent, and some have the recommendations revised. Policy changes also potentially play a part in the way drugs are prescribed and used.

An aging population is offered as an explanation, as individuals over 40 tend to take more prescriptions than those that are younger. However, when adjusted for age, the numbers still show a significant growth in prescription drug use.

The findings are pulled by data gathered by the National Health and Nutritional Examination Survey, which samples around 5,000 people each year, and asks participants about their prescription drug use. Data from 2012 is the most recent numbers available.

The CDC cites the growth of third party insurance, increased marketing to doctors, over-prescribing of antibiotics, and growing abuse of prescription painkillers as reasons for the increase.