KAHULUI, Hawaii (KHON2) — Police are warning the public after several people overdosed on a blue pill believed to be oxycodone. Authorities obtained this information throughout September.

According to the Maui Police Department, the blue pills were suspected to be laced with fentanyl.

During their investigation, over 400 blue pills that were stamped “M30” were recovered from an adult male on Friday, Oct. 2. The blue pills are also known as “K9.”

Officials said that a presumptive laboratory test revealed that the recovered pills were fentanyl and not oxycodone.

Police added that there are still over 500 fentanyl pills that are unaccounted for and are believed to be on Maui.

Fentanyl is known to be a powerful opioid. Officials said that it’s 80 to 100 times more potent than morphine. MPD said that these counterfeit pills are believed to be supplied by Mexican cartels and that these pills look identical to prescription medication.

Officials said that it only takes two milligrams of fentanyl to be fatal.

Authorities did not provide further details but said that the investigation is ongoing.