A prescription drug company just got caught making a massive donation to oppose legalizing marijuana in Arizona.

A massive cash donation from a prescription drug company to fight against marijuana legalization has cannabis activists charging that Big Pharma has it in for legal pot.

This fall Arizona will be one of five states voting to legalize recreational marijuana, and campaign finance reports recently revealed that the pharmaceutical company Insys Therapeutics has donated $500,000 to Arizonans For Responsible Drug Policy, the primary group fighting a recreational marijuana legalization measure in the state.

Typically the face of such campaigns have been religious conservatives or tough-on-crime politicians, but as medical marijuana has begun to take a bite out prescription drug sales, those with financial skin in the medicine game have begun to take a more public role in keeping pot illegal.

“It appears they are trying to kill a non-pharmaceutical market for marijuana in order to line their own pockets,” says J.P. Holyoak, chair of the Campaign to Regulate Marijuana Like Alcohol, in a statement released Thursday morning.

If marijuana reform advocates were looking for a nefarious Big Pharma company to play the role of villain in this campaign, they certainly found a friend in Insys Therapeutics.

The manufacturers of fentanyl—one of the most potent and addictive pharmaceutical opioids on the market—Insys has been the target of multiple state and federal investigations for marketing the drug to patients who don’t need it, pressuring doctors to overprescribe it, and training employees to pretend they’re doctors when asking insurance companies to cover it. All while banking hundreds of millions on the sale of a profoundly addictive drug.

Insys Therapeutics did not respond to requests for comment on this story.

“Our opponents have made a conscious decision to associate with this company,” says Holyoak. “They are now funding their campaign with profits from the sale of opioids — and maybe even the improper sale of opioids. We hope that every Arizonan understands that Arizonans for Responsible Drug Policy is now a complete misnomer. Their entire campaign is tainted by this money. Any time an ad airs against Prop. 205, the voters should know that it was paid for by highly suspect Big Pharma actors.”

The donation from Insys is hardly the first instance of pill peddlers injecting themselves into marijuana reform.

In 2014, The Nation published an long-form article revealing that the makers of Oxycontin and Vicodin were two of the largest contributors to The Partnership For Drug Free Kids (remember the “this is your brain on drugs commercial”?), and that the Community Anti-Drug Coalition of America (CADCA), one of the largest of their kind in the nation, is also sponsored by opioid manufacturers Purdue Pharma.

Groups like CADCA and The Partnership stress the dangers of marijuana and often hold influence over voters and legislators considering its legalization.

This summer, the Washington Post reported that a pharmaceutical company possibly influenced the DEA’s decision to reject a Department of Health and Human Services recommendation that THC be reclassified.

But why, you may ask, do pharmaceutical companies care whether or not marijuana is legalized?

Well, a recent study at the University of Georgia has confirmed what anecdotal evidence has asserted for years, that in states where medical marijuana is legal and accessible, significantly fewer people are using prescription drugs, particularly painkilling opioid drugs.

“The people in our study are voluntarily choosing to forgo prescription medication in favor of marijuana,”said W. David Bradford, a professor who researches pharmaceutical economics at the University of Georgia.

He and his daughter Ashley co-authored the report looking at 17 states with medical marijuana, and found that prescriptions for drugs treating nausea, anxiety, seizures and chronic pain, among others, dropped significantly from 2010 to 2013. In the case of pain, there were more than 1800 fewer prescriptions filled.

And it’s likely that the study is lowballing that number.

After all, the Bradfords only looked at Medicare Part D for their study, which is used by seniors, the demographic least likely to consume marijuana. Bradford said the intention was to get a conservative estimate since this was the first study of its kind. “We were surprised in that the findings were much larger than we expected.”

Ashley Bradford is currently looking into medical marijuana’s impact on Medicaid prescriptions, as Medicaid is used more commonly by young people, who also are more likely to use medical marijuana.

The most current numbers suggest significant savings on the part of Medicare due to medical marijuana, Bradford said, and significant losses to pharmaceutical companies.

For anyone without financial ties to Big Pharma, this is great news. After all, we’re talking about drugs that are the leading cause of accidental death in the U.S., killing 44 of our citizens every day, enslaving millions to addiction each year, and have been on a steady climb since 2001.

Considering the PR nightmare that is the opioid epidemic, and the inevitability of marijuana legalization, many pharmaceutical companies have begun sniffing around the cannabis market, smelling cash where they once smelled competition.

Unfortunately, this is often in the form of synthetic marijuana—not the same synthetic street garbage sending people to the hospital, but still not a plant form of cannabis. These synthetic drugs have been criticized as being medically inferior to the real deal, and would likely be less in demand if naturally derived cannabis became legal.

Not surprisingly, Insys Therapeutics, the company spending a half mill to defeat legalization in Arizona, has invested in the development of synthetic cannabinoids.

Professor Bradford says he was surprised to learn that the pharmaceutical industry was fighting marijuana at all. “If marijuana was rescheduled, and you’re the first pharmaceutical company to the FDA showing your formulation of marijuana is beneficial for a condition . . . that’s worth a lot of money. I would think the pharmaceutical companies would see this as an opportunity to have a new blockbuster drug.”