These Rules make amendments to the Prison Rules 1999 (S.I. 1999/728) (“the Prison Rules”) and the Young Offender Institution Rules 2000 (S.I. 2000/3371) (“the YOI Rules”). The amendments reflect the changes made by the Prisons (Substance Testing) Act 2021 (c. 18). That Act, which entered into force on 9 December 2021, introduced changes to improve the capability of prisons in England and Wales to test for the use of illicit substances by prisoners. Prior to the changes made by that Act prisons could require prisoners to provide a sample for any “controlled drug” or “drugs specified” in the Prison and YOI Rules. New drugs could be added to the list of those that could be tested for but only by making amendments to the rules by secondary legislation. Due to the chemical composition of psychoactive substances, in particular, being subject to rapid change this meant repeated amendments were needed in response to small changes in substance composition. The changes being made by these Rules mean that tests can be carried out for the broader generic definition of psychoactive substances and “prescription only medicines” and “pharmacy medicines” introduced by the 2021 Act. The changes made by these Rules will help staff in Her Majesty’s Prison and Probation Service (HMPPS) and other agencies to understand the full extent and nature of substance misuse in prisons, and to take appropriate action to prevent it.