Originally Posted by
onlythetruth 
They didn't do it because they CAN'T do it, TU. Research ethics these days do not allow researchers to "deny treatment" to people with mental health issues, thus making it difficult, if not impossible, to use control groups in such experiments.
I'm sure they could have found plenty of addicted people who had no interest in treatment to serve as a control group. As long as they were informed that they were not going to receive treatment for their addiction, it would have been ethical. Those who chose to participate as a control group would just be doing what they usually do anyway.