Los Angeles Angels pitcher Tyler Skaggs had drugs and alcohol in his system at the time of his death, which was accidental, a coroner's report says.
Skaggs died after choking on his own vomit, Tarrant County medical examiner's office said.
The 27-year-old had high levels of opioids, including fentanyl and oxycodone, in his body, toxicology results showed.
Skaggs was found dead at a Hilton hotel in Southlake, Texas, on 1 July.
He was discovered fully clothed on his bed with no signs of trauma, police said.
His death was confirmed just hours before the Angels were scheduled to begin a three-game series against the Texas Rangers.
In a statement, Skaggs's family said drug use was "completely out of character" for the pitcher.
The family thanked police for investigating his death, but said they were "shocked to learn that it may involve an employee of the Los Angeles Angels".
"We will not rest until we learn the truth about how Tyler came into possession of these narcotics, including who supplied them," the family's statement said.
The family said it had hired a lawyer to determine how Skaggs obtained the drugs.
Southlake Police said it did not suspect foul play and was not investigating any criminal allegations.
Angels general manager Billy Eppler said the club was "actively cooperating" with the investigation but would not comment on the family's statement.
"We miss Tyler every day. That clubhouse misses him every day," Mr Eppler said.
"Nothing we learned today changes those feelings. Not one bit. But this is like a shot to our core. And it brings back a lot of pain for that tragic day."
Born in the Los Angeles neighbourhood of Woodland Hills, Skaggs made his Major League Baseball (MLB) debut aged 20 for Arizona Diamondbacks.
In his last season for Angels, Skaggs started 15 games, most recently on 29 June against the Oakland Athletics.