An embattled pharmaceutical company that sells the powerful painkiller fentanyl has donated $500,000 toward defeating a ballot initiative that would make recreational use of marijuana legal under Arizona law.

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.

Insys currently markets just one product, according to an August filing with the Securities and Exchange Commission: a sublingual fentanyl spray it calls Subsys.

Fentanyl Maker Donates Big to Campaign Opposing Pot Legalization