If the government tightens up on drug dealers and raises the costs of dealing illegal drugs, then the drug addicts' dollar expenditures to feed their addiction will tend to

This is a fairly simple concept. If the government were to tighten up on drug dealers and raise the cost of dealing illegal drugs, the job of drug dealers to distribute their products would be harder. The cost to buy drugs for drug addicts would be more expensive. So, the dollar expenditures for drug addicts would increase as they feed their addiction.