I am not aware of any specific instance where difficulties have arisen in a prison because staff were not informed when prisoners were on medication. However, I understand that the Prison Officers' Association has expressed some concern on this issue in recent times.
Generally speaking, information about the medication prescribed for an offender is a matter between the prison doctor and patient. Where an offender is given medication which might affect his or her co-ordination or alertness, a procedure is in place, (1) to inform the patient of the potential side effects and (2) to notify the prison authorities that the offender is receiving medication which might affect safety in, say, a workshop environment. This policy was reiterated and formalised in a circular to prison doctors and governors issued by the Director of Prison Medical Sevices on 9 June 1993.