Abstract: Restricting availability is the major response to illicit drugs in most Western countries including Australia. Prohibition may reduce harm when the drug in question is in low demand, controls are difficult to subvert, and when similar drugs are less toxic or unavailable. However, the health, social and economic costs of supply reduction are substantial and increasing for both injecting drug users and the general community. Population adjusted mortality of heroin users has doubled in Australia in the last decade. The possible impact of supply reduction policy on the spread of HIV infection among IDUs is an important but largely neglected consideration. The effectiveness of supply restriction policy in decreasing the availability of drugs or in reducing drug-related harm is unlikely to be increased significantly by more vigorous implementation of supply reduction or adoption of new technology. Conversely, on the basis of existing data, greater availability of HIV prevention measures attractive to the target population (including especially drug treatment such as methadone maintenance) is likely to be effective and cost-effective. The costs and benefits of innovative methods of providing currently illicit drugs to those who are determined to use them requires careful evaluation and comparison with existing policies. Policy on illicit drugs in most countries including Australia is still dominated by concern about drug use rather than focused on the need to reduce drug-related problems, which is the agreed aim of national drug policy.