They will be expensive because bribes, transport inefficiencies, rewards of special risk, and so forth, all raise the costs of bringing drugs to market. Therefore much of the begging, prostitution and street crime that inconvenience Western cities. They will be dirty because illegal markets lack the usual safeguards of quality. Nor will caustic soda be used to make it fizzy. Brewers have too much to lose by poisoning or defrauding customers.
Drug dealers can afford to be less particular.
Therefore frequent overdosing. Therefore poisonous additives. Therefore, the frequent transmission of aids even today by the sharing of dirty needles. Moving from the costs of the crime resulting from illegality, we come to the costs of enforcement. These also are massive.