It is common to have dreams about using drugs, especially when you are withdrawing, quitting or craving a drug that you are addicted to. The subconscious, just like the conscious mind, still has the intense desire for the drug. And yes, like sexual "wet dreams," these dreams can be disheartening when you wake up without Jessica Alba (or a 8 ball of coke) in bed with you. I have heard from severe addicts that during their stay at rehab these dreams occurred for weeks, or even longer. It's scary, that even during sleep, a substance can have your undivided attention.