That the patient is taking

National Institute of Clinical Excellence (NICE) describe the process of medicines reconciliation within secondary care as follows ‘the aim of medicines reconciliation on hospital admission is to ensure that medicines prescribed correspond to those that the patient is taking before their admission. Details to be recorded include the name of the medicine(s), dosage, frequency and route of administration. Establishing these details may involve discussion with the patient/ carer and the use of records in primary care. This does not include medicines review.’
https://www.sps.nhs.uk/wp-content/uploads/2017/07/Medicines-Reconciliation-Training-Trainer-Copy_Sept-14.pdf

is "that the patient is taking before their admission" a relative clause functioning as an adjective answering question which one?
why can't we use "that the patient takes..." rather than " that the patient is taking...2?