Editing Controlled Substances Act (section)

== Analogues vs Markush descriptions ==
Historically, in an attempt to prevent psychoactive chemicals which are chemically similar to controlled substance, but not specifically controlled by it, the CSA also controls "analogues" of many listed controlled substances. The definition of what 'analogue' means is kept deliberately vague, presumably to make it harder to circumvent this rule, as it's not clear what is / is not controlled, thus placing an element of risk and deterrent in those performing the supply. It is up to the courts to then decide whether a specific chemical is an analogue, often via a 'battle of experts' for the defense and prosecution which can lead to extended and more uncertain prosecutions. The use of the 'analogue' definition also make it more difficult for companies involved in the legitimate supply of chemicals for research and industrial purposes to know whether a chemical is regulated under the CSA<ref>{{Cite web |title=Controlled Drugs and analogues |url=https://blog.scitegrity.com/news/list-of-controlled-drugs-and-analogues}}</ref>

Starting in 2012, with the [[Synthetic Drug Abuse Prevention Act|Synthetic drug abuse prevention act]], and later an amendment to the CSA in 2018 [https://www.ecfr.gov/current/title-21/chapter-II/part-1308/subject-group-ECFRf62f8e189108c4d/section-1308.11#p-1308.11(h)(i) defining fentanyl chemical space], the CSA started to use [[Markush structure|Markush]] descriptions to clearly define what analogues or chemical space is controlled. These chemical space, chemical family, generic statements or markush statements (depending on the legislation terminology) have been used for many years by other countries,<ref>{{Cite web |title=An overview of chemical space laws and controlled drugs |url=https://blog.scitegrity.com/news/controlled-substances-lists-and-chemical-families}}</ref> notably the UK in the [[Misuse of Drugs Act 1971|Misuse of Drugs Act]].  

These have the advantage of clearly defining what is controlled, making prosecutions easier and compliance by legitimate companies simpler. However the downside is that these tend to be harder to understand for non-chemists and also give those wishing to supply for illegitimate reasons something to 'aim' for in terms of non-controlled chemical space. For both Markush and analogue type approaches, typically computational systems<ref name=":0" /> are used to flag likely regulated chemicals.