It has been revealed that the maker of a powerful, addictive opioid drug is bankrolling the opposition to the effort to legalize and regulate marijuana for recreational use in Arizona.

The Phoenix New Times reported Thursday that Insys Therapeutics, the company behind the fentanyl-based medication Subsys, made a $500,000 donation to the group Arizonans for Responsible Drug Policy (ARDP), which is leading the campaign against Proposition 205.

On the ballot in November, Prop. 205 would allow people 21 years of age or older to possess up to one ounce of marijuana and grow up to six plants in their homes as well as establish a department to regulate the drug's cultivation and sale.

It appears that Insys is trying to "eliminate the competition," according to the New Times, which noted that the company "expects to soon launch a pharmaceutical version of THC, the main psychoactive ingredient in cannabis."

What's more, Insys is currently facing numerous state investigations for deceptively marketing and selling Subsys, which is intended to treat cancer pain, and coercing doctors to promote it to patients for off-label uses. Fentanyl is estimated to be 80 times as potent as morphine and hundreds of times more potent than heroin, according to the Centers for Disease Control and Prevention, and may be fatal to users.

"It's hard to imagine a more sinister donor than Insys Therapeutics Inc. in the eyes of pot legalization proponents, who long have claimed drug companies want to keep cannabis illegal to corner the market for drugs, some addictive and dangerous, that relieve pain and other symptoms," U.S. News & World Report wrote Thursday, summarizing the dynamic.

Responding to the news, J.P. Holyoak, chair of the Prop. 205 proponent group Campaign to Regulate Marijuana Like Alcohol, issued a press statement slamming the opposition to keeping the donation from "one of the more unscrupulous members of Big Pharma."

"You have a company using profits from the sale of what has been called 'the most potent and dangerous opioid on the market' to prevent adults from using a far less harmful substance," Holyoak said.

He also pointed out their development of synthetic 'pharmaceutical cannabinoids,' and said, "It appears they are trying to kill a non-pharmaceutical market for marijuana in order to line their own pockets."

"Our opponents have made a conscious decision to associate with this company. They are now funding their campaign with profits from the sale of opioids — and maybe even the improper sale of opioids," Holyoak continued. "Any time an ad airs against Prop. 205, the voters should know that it was paid for by highly suspect Big Pharma actors."