Three Inca children found mummified atop a 20,000-foot volcano in South America consumed increasing amounts of coca leaf and corn beer for up to a year before they were sacrificed, according to a new study.

Sedation by the plant and alcohol combined with the frigid, high-altitude setting may explain how the children were killed. There is no evidence for direct violence, the researchers noted.

The coca leaf and corn beer consumption rises about six months before death and then skyrockets in the final weeks, especially for the eldest, a 13-year-old girl known as the “Ice Maiden.”

“She was probably heavily sedated by the point at which she succumbs to death,” Andrew Wilson, an archaeologist at the University of Bradford in the United Kingdom and the study’s lead author, told NBC News.