Would you please explain to me the last sentence?

Treatment availability and policy focused on demand reduction rather than supply reduction is a growing trend in national drug policy, especially since intravenous drug users are at high risk of HIV/AIDS infection. However, criminal enforcement remains the central theme in world drug policy

Thanks

The last sentence suggests that what it is all about regarding policy (so the laws, and practices of people doing the government's work, like courts, police, and public agencies) for drugs is their illegality. Drugs are illegal and it's all about busting users and sellers.

For the other part, which is difficult to understand, it says that reducing the number of people who want drugs is increased, instead of trying to crack down on drugs available or coming into the country (supply). Reducing demand means fewer people want drugs (so by treatment or whatever), and this type of policy is going up. One reason is to reduce HIV.

Basically, for drug policy, all policy relates to enforcing laws, but some policy to reduce the number of drug users is increasing, but older policy to crack down on drug supply is less prominent now.

Hope that helps.

The whole passage is saying that more attention is being paid to treatment for drug problems and ways to reduce demand than on reducing the amount of drugs being made and sold; but more than any of those programs or methods, worldwide the main way of handling the drug problem is through criminal prosecution, arrests, prisons, et cetera..