Clearly, you have a negligence claim against the other driver. He failed to follow the Rules of the Road. He ran a stop sign. Then, you learn more. You learn this other driver also uses illegal drugs. Illegal drug use. That’s powerful evidence. It’s powerful evidence if the judge allows it’s use at trial! That brings us to the key question: Is the other driver’s drug use admissible at trial? Can you use this evidence to help your case?
The answer is, maybe. I know, that’s not the concrete answer you wanted. Evidentiary questions rarely have absolute answers. That’s why a good lawyer with real trial experience is so important to your case. You need an experienced trial lawyer who understands the evidence rules and how to apply them. You certainly will NOT get such a lawyer from the billboards and television advertisements showing smiling attorneys begging for cases.