there has been opiated hash around in the past but it was very specialty and you paid more for the privilege. There is absolutely no upside to lacing weed with drugs like coke or heroin. there is a ceiling on how much folks will pay for weed, and dumping a drug that cost 3x5 times as much into your stash, doesn't make sense. Besides, people either already have coke or heroin or they dont. You either go for the real mcoy and add it t0 you bud or you abstain.
Then of course there is the fact that weed has just been LEGALIZED. Why would you make it illegal again by adding scheduled norcotic, especially if you operate a shopfront.