By "drug-related crimes" are you referring to crimes of trafficking, or crimes committed while under the influence (because the perpetrator is under the influence).

For the former, I don't see how it could do anything but decrease. As to the latter, I suspect initially it would go up, but I don't think that would last. And, the drop off in crimes related to trafficking would more than make up the difference. Having said that, crimes related to trafficking do tend to be heavily concentrated into fewer areas, so the typical suburban white fear-loving voter would probably perceive that crime has gone up.