This article is actually a summary of a larger article in The Nation, and BusinessInsider presents it this way: Last week, The Nation published an interesting look at who's driving the fight against the legalization of marijuana. Pharmaceutical companies that make billions off painkillers and police unions are two big heavy hitters in the fight against marijuana legalization. They throw their monetary support behind groups that fight legislation that would legalize pot — even medical marijuana — and lobby Congress. The Nation pointed out that the Community Anti-Drug Coalition of America and Partnership for Drug-Free Kids among other groups were funded by "opioid manufacturers and other pharmaceutical companies."
What would be the reason for such stances? The obvious answer is that marijuana could become a formidable challenge to the bottom line of drug companies manufacturing various branded prescription painkillers.