Insys Therapeutics, a pharmaceutical company that was one of the chief financial backers of the opposition to marijuana legalization in Arizona last year, received preliminary approval from the Drug Enforcement Administration this week for Syndros, a synthetic marijuana drug.

Insys gave $500,000 last summer to Arizonans for Responsible Drug Policy, the group opposing marijuana legalization in Arizona. The donation amounted to roughly 10 percent of all money raised by the group in an ultimately successful campaign against legalization. Insys was the only pharmaceutical company known to be giving money to oppose legalization last year, according to a Washington Post analysis of campaign finance records.

Syndros is a synthetic formulation of THC, the main psychoactive component in the cannabis plant. It was approved by the FDA last summer to treat nausea, vomiting and weight loss in cancer and AIDS patients. The DEA approval places Syndros and its generic formulations in Schedule II of the Controlled Substances Act, indicating a “high potential for abuse.” Other Schedule II drugs include cocaine, morphine and many prescription painkillers.

Whole-plant marijuana remains in Schedule I of the CSA, an even stricter regulatory category that designates a lack of medically accepted use in addition to a high abuse potential.

Insys has been active in marijuana policy for several years. In 2011 it wrote to the DEA to express opposition to loosening restrictions on naturally derived THC, citing “the abuse potential in terms of the need to grow and cultivate substantial crops of marijuana in the United States.”

Last year it petitioned the DEA to loosen restrictions on synthetic versions of CBD, another compound in the cannabis plant. The company is currently developing a CBD-based drug to treat pediatric epilepsy.

“It appears they are trying to kill a non-pharmaceutical market for marijuana in order to line their own pockets,” a spokesman for Arizona's marijuana legalization campaign said of Insys last year.

The company last year said that it opposed the marijuana legalization measure because “it fails to protect the safety of Arizona’s citizens, and particularly its children.” But it added that it “firmly believes in the potential clinical benefits of cannabinoids,” and that “we hope that patients will have the opportunity to benefit from these potential products once clinical trials demonstrate their safe and effective use.”

Insys is also the subject of numerous state and federal criminal investigations, as well as a shareholder lawsuit, over its aggressive marketing of a product containing the potent and deadly opioid painkiller fentanyl. In December, the FBI arrested the company's former chief executive and five other executives on charges that they “paid kickbacks and committed fraud to sell a highly potent and addictive opioid that can lead to abuse and life threatening respiratory depression.”

In addition to its synthetic marijuana products, Insys is also developing a drug to treat opioid overdose.

The company did not immediately respond to a request for comment.