 This same study showed that saliva testing could detect other drug metabolites, as well, although not as frequently as urine testing; this was the case for morphine, other benzodiazepines, cannabis, and cocaine.One often cited criticism of using saliva as a diagnostic fluid is that biomarkers are present in amounts that are too low to be detected reliably.As Wong points out, however, this “is no longer a limitation” due to the development of increasingly sensitive detection techniques.