40.3 million.  Let that number sink in for a moment.
That number, according to the National Committee for Quality Assurance (NCQA), represents the number of people from the US, aged 12 years or older, who in 2020 were identified with a substance use disorder, either an alcohol use disorder or an illicit drug use disorder.
That represents 14.5 percent of the population.
SAMHSA reported that in 2022, 23.1 percent of the US population, had a mental illness.  That is 59.3 million people.
At some point there is an intersection between these two numbers.  We see them all the time.
Many of us who treat individuals for mental health disorder face the challenges of co-occurring substance use disorders.  This has the potential for significantly undermining the work we are doing with our clients as they continue to address their symptoms with illicit drugs or alcohol.  SAMHSA reports that 21.5 million individuals were identified with co-occurring disorders in a survey conducted in 2022.
Screening for substance use, of course, should be a thing that we do at the outset of treatment.  It should be a part of our initial assessment.  But how many of us ask about substance use after that?
While certainly we don’t want to be in a position to be constantly assessing for substance use when there has been no evidence of particular substance use issues, a study published in the Journal of Studies on Alcohol and Drugs reported that individuals in treatment who were assessed on use more frequently reported greater reductions in substance use, including a higher prevalence in abstinence, than those individuals assessed less frequently.
So, at least is this randomized study of 253 participants, it was found that there was at least a correlation between assessment and improvement.  While the researchers admit that a more research is needed prior to drawing conclusions, they found the results of this study to be clinically meaningful.  
As we think about our work as clinicians, it is easy to find ourselves very focused on the engagement and active treatment, and we might lose track of our capacity to assess.  It is interesting that, at least with substance use, there is a possibility that the assessment process might even have a therapeutic effect.