In order to assess whether a medicine(s) in use on a study falls in the category of an IMP and therefore would require a Clinical Trial Authorisation (CTA), the MHRA has produced a 5-step algorithm which can be found on pages 8-9 in a document on the MHRA website.If you have any doubts about the answer to any of the questions contact the Clinical Trials Unit at the MHRA.For general enquiries: clintrialhelpline@mhra.gsi.gov.uk or 020 7084 2456 (Monday - Friday 08:30-16:30)For enquiries regarding documents and submissions: RIS.CT@mhra.gsi.gov.ukFor enquiries on fees: cashiers@mhra.gsi.gov.uk or 020 7084 2524