OK, I think I may have found a link that may shed some light on this. I did some googling to see if there was any recent connection between hydroquinone and the DEA. I found this drug fact sheet from the DEA website. It's a fact sheet for opium:
I can't copy and paste from a pdf sheet, but here is the relevant text:
I think in this case adding hydroquinone to the list was a typographical error, as I don't believe ingesting it will get a person high, just very sick. However, these lists are distributed to people who do business with the DEA, such as retailers of chemicals. I guess it's possible that hydroquinone might become very hard or impossible to get for a while until all this gets straightened out.Drugs causing similar effects
morphine, codeine, heroin, methadone, hydroquinone, fentanyl, and oxycodone.