We should do the same thing we did at the end of prohibition when the government was broke and decided legalising and taxing alcohol would balance their budgets. Take a substance that the US Government ruled to be illegal to use (say Marijuana), that has a large base of illegal users, and then make it legitimate, tax it, and regulate its use to mitigate any safety concerns. It's a double whammy, you cut down on your DEA expenses fighting it and you reap the benefits of taxing it's users.