Because the study design is observational and the data are cross-sectional, no strong causal conclusions can be drawn. However, there is evidence of lower marijuana use in the presence of SDT, and evidence of higher use of illicit drugs other than marijuana. Until further research can clarify the apparent opposing associations, schools should approach SDT with caution.
There is no evidence base to support drug testing so why is it so heavily promoted and embraced?
See on www.jahonline.org