Are there any statistics available showing the percentage of patients who are prescribed anti-depressants/anti-anxiety medications during or after substance abuse rehab programs?

I had a discussion with a friend of mine whose boyfriend had completed a drug rehab program. Long story short, she and I have different theories on what percentage of people in drug rehab are prescribed anti-anxiety or anti-depressant medications. My thoughts are that the majority of people who are in these programs are prescribed medications to help them through, help them stay positive, help them with the transition to a lifestyle that does not include alcohol and illegal drug use. She said she does not think that the majority are prescribed medications. I used to work in a field that dealt with people who attended substance abuse programs, and so I have seen many, if not all, come out with prescriptions for such meds. However, that in and of itself does not prove a debate.

Are there any statistics available showing the percentage of patients who are prescribed anti-anxiety and anti-depressant medications during/after substance abuse rehab programs?