There is an increasing problem with benzodiazepine co-abuse in the opiate dependent population of Dublin. The importance of early detection of this co-abuse is essential as there is an increased risk of dangerous injecting practices such as sharing of needles and criminality in those who co-abuse benzodiazepines and opiates. This study was carried out in the National Drug Treatment Centre, Dublin. It aims to describe the current difficulties in identifying the co-abuse of short acting benzodiazepines including flunitrazepam in a cohort of opiate dependent patients. Using a sample of those attending the clinic it was discovered that standard methods of urinalysis failed to identify 10% of co-abuse. For those patients whose abuse of flunitrazepam is undetected on screening, clinical interventions which aim to minimise the consequence of the co-abuse and reverse the chaotic drug using patterns fail to be put in place at the earliest possible time.