The detection of the psychoactive morphine alkaloids in the urine may have legal repercussions. This study has examined new approaches to differentiate between licit and illicit opiate-product use. The work examined the use of marker compounds with the following objectives: investigating claims of legal opiate product use plus non-psychoactive medicinal products, looking for new specific opiate use markers, and investigating the effect of opiate dose preparation method on the availability of marker compounds to the user. A GC-MS method has been developed to quantitatively determine meconin and hydrocotarnine (two constituents of opium and, heroin) in urine. Using the optimised method, the levels of the two compounds were measured in a large number of opiate-positive urine samples, and the results were compared with previous literature data on opiate marker compounds. The extent of noscapine GC-MS thermal degradation to meconin and hydrocotarnine was investigated in order to assess noscapine potential contribution to the concentrations of meconin and hydrocotarnine in urine.