New details from a toxicology report from Prince’s autopsy revealed he had an “exceedingly high” concentration of fentanyl in his body at the time of his death back in 2016.

Prince was found dead in an elevator at his estate in  Minnesota, on April 21, 2016. In June that year, a toxicology report was released that stated that Prince died from an accidental overdose of fentanyl.

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Fentanyl is a powerful synthetic opioid analgesic, it is similar to morphine but it is 50 to 100 times more potent.

A year after his death, released court documents revealed that investigators found a number of prescription drugs hidden away inside Prince’s Paisley Park estate. Aside from his medication, investigators also discovered opioids in multiple areas around the home and stored in containers other than pill bottles, such as vitamin bottles.

The concentration level of fentanyl in the singer’s blood was 67.8 micrograms per liter. This is significantly higher than other documented fentanyl deaths, the report explains that people have died with blood levels ranging from three to 58 micrograms per liter.

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The report also stated Prince had a fentanyl level of 450 micrograms per kilogram in his liver, which is significantly higher than most cases. The report explains that overdose or fatal toxicity occurs when the liver concentrations is greater than 69 micrograms per kilogram.

Experts say that there is no “lethal level” of fentanyl. A person who takes prescription opioids for a long time builds up a tolerance, so a dose that could kill one person might help another.