Story highlights Most of the adulterated products were marketed for sexual enhancement, analysis finds

The supplements could harm the health of those who take them, authors said

(CNN) Nearly 800 dietary supplements sold over the counter from 2007 through 2016 contained unapproved drug ingredients, a new analysis of US Food and Drug Administration data found. More than one unapproved pharmaceutical ingredient was found in 20% of those supplements, the study published Friday in JAMA Network Open showed.

The presence of prescription medicines, often at unknown concentrations, means these supplements are essentially "unapproved drugs" that could be harmful to users' health, according to the study authors.

"These products have the potential to cause severe adverse health effects owing to accidental misuse, overuse, or interaction with other medications, underlying health conditions, or other drugs within the same dietary supplement," wrote the authors, led by Madhur Kumar of the California Department of Public Health Food and Drug Branch.

More than 50% of adults use dietary supplements, a $35 billion industry, notes the study.

Kumar and his co-authors reviewed the FDA's Tainted Products Marketed as Dietary Supplements_CDER database for 2007 through 2016. The database is maintained on the agency's website as a resource for consumers and to increase transparency and public knowledge. The researchers performed the new analysis independent of the FDA.