We are in the middle of trial and are trying to see if there is any caselaw where a DRE can testify to the additive effects of (prescription) drugs and alcohol? There wasn't a formal drug investigation but the defendant admitted to taking the drugs prior to consuming alcohol.
Thanks!

I don't know about the specific case law, but they are required to be able to explain the effects of combinations of substances including alcohol during the "knowledge exam" section during their training and certification. The training process is recognized nationally and DREs are recognized as experts in several areas by various trial courts, so it would seem that we could qualify one as an expert to testify in this area.

The DRE has training and logged experience on those exact issues. You will have to satisfy the court as to your DRE's qualifications, but their training is extensive and part of a curriculum created by a panel of way overqualified national medical experts. Make sure to provide you DRE with all of the evidence in your case, reports, videos, sfst's etc.