Tessie Sanchez, a spokeswoman for the Dominican attorney general's office, told The Associated Press toxicology reports showed Taveras had a blood-alcohol level five times the country's legal limit when he lost control of his car Oct. 26 on a highway in the tourist region of Puerto Plata.
The 22-year-old Taveras was "legally intoxicated when he crashed," Sanchez said.
"Until we have the opportunity to review the official report, we cannot confirm details," Cardinals general manager John Mozeliak said in a statement.
"While we are still working to obtain the facts, it won't change the fact that this is a terrible tragedy. We have an obligation to use this as an opportunity to educate our players that they must take responsibility for themselves both on and off the field," he said.
Taveras hit .239 with three homers and 22 RBIs in 80 games this year. He homered against the Giants in his major league debut on May 31. He also had a big solo drive in the seventh inning of Game 2 in the NL Championship Series against San Francisco.
Taveras held a Canadian passport. He spent four years as a teenager living in Montreal with his father, Francisco Taveras, and played for the Marquis de Montreal of the Quebec midget triple-A league before moving back to the Dominican Republic.
Taveras was a teenager when he signed with the Cardinals as an international free agent in 2008. Before this season, he was ranked the No. 3 overall prospect by MLB.com and Baseball America.
He was buried late last month in a cemetery near the Dominican Republic's north coast.
Taveras' 18-year-old girlfriend, Edilia Arvelo, was in his 2014 Chevy Camaro when it ran off the road. She also died.
A month into the 2007 season, St. Louis pitcher Josh Hancock was killed in a car crash and tests showed his blood-alcohol level was nearly twice Missouri's legal limit. The Cardinals subsequently banned alcohol from their clubhouse.