The real issue is going to be that you did drugs, not the technicalities of what specific law you broke. You're not gonna get arrested for doing drugs 3.5 years ago in college, but you are going to have to convince the department that you are no longer at risk for using them. One of the issues with LE applicants and drug use is the concern that people who used drugs before might be tempted to use them again after being put in the high-stress LE environment. If it was just marijuana use, nobody really cares as long as you are honest about it. Other drugs, well it depends on the department and the circumstances. Your best bet is to just be honest, especially since they are probably going to polygraph you anyway. If they won't hire you, keep trying- someone might eventually, especially as more time goes by. A good, solid work history since the drug use with no substance abuse problems will probably help a lot.