Substance testing in Violence and Harassment cases

Hello,
I have been asked if it is legal or appropriate to substance test both the accuser and accused in a harassment or violence-related case? If it is, is it legal or appropriate to use those results to determine the level of severity of the incident? I guess I’m being asked if there are examples of cases where it was determined that the accuser had ‘thin skin’ due to being hung over or otherwise under the influence and the case was not determined to be a valid claim.