A temporary class drug is a relatively new status for controlled drugs, which has been adopted in some jurisdictions, notably New Zealand and the United Kingdom, to attempt to bring newly synthesised designer drugs under legal control. The controlled drug legislation in these jurisdictions requires drug scheduling decisions to follow an evidence-based process, where the harms of the drug are assessed and reviewed so that an appropriate legal status can be assigned. Since many designer drugs sold in recent years have had little or no published research that could help inform such a decision, they have been widely sold as "legal highs", often for months, before sufficient evidence accumulates to justify placing them on the controlled drug schedules.