The Bureau of Forensic Sciences of Puerto Rico tells us, based on Taylor's lab results, it was determined his cause of death was MDMA poisoning. They also found traces of ketamine in his system.

TMZ broke the story -- Taylor was found unresponsive in his room back in January -- witnesses told us he was seen earlier in the night being carried off the dance floor by two other men. We were told he'd consumed multiple substances.

The cruise Taylor was on was full of celebs, with performances from Olivia Newton-John and Galantis.

Several people had been arrested prior to boarding the ship in Ft. Lauderdale for drug possession.