During the 20th century, support for a deontological approach to illicit drugs grew steadily. As a deontological framework was invoked, how goals were accomplished was considered more important than what was achieved. Accordingly, global drug prohibition was considered right even though illicit drug production and consumption, deaths, disease, crime and official corruption increased steadily. In the last decades of the 20th century, consequentialist approaches to drugs began to receive increasing support. Drug policy was now considered morally right if it produced predominantly beneficial consequences. The advent of an HIV pandemic in the last quarter of the 20th century changed the nature of injecting drug use irrevocably, just as injecting drug use changed the course of the HIV epidemic. HIV spread among injecting drug users led to increased support for ‘harm reduction’. The scientific debate about harm reduction, which is now over, has essentially been between consequentialists and their deontological critics. The paramount aim of harm reduction is to reduce the health, social and economic costs of drug use. Reducing drug consumption can be a means to this end. Harm reduction strategies have been recognized as being effective, safe and cost-effective for at least 15 years. The paramount need now is to overcome the conventional reliance on drug law enforcement, the major barrier to implementing harm reduction strategies in time and on sufficient scale. Because of the limited benefits, high costs and severe unintended negative consequences of global drug prohibition, increasing consideration is being given to possible alternative arrangements for drugs.