Authorities had suspected that Michael Bryan killed himself by leaping from an eight-story balcony in Los Angeles in February.
The 18-year-old college student left behind a suicide note, but the coroner's office wanted toxicology results before ruling on his cause of death. The findings were released Wednesday.
Bryan was one of five children that Ismond and her ex-husband adopted. Her publicist, Nicole Perez, was not immediately available for comment.
Osmond and her brother, Donny, took a brief break from their Las Vegas show before returning with a teary tribute to Bryan in March.