Repeated Swallowed THC Was Poorly Captured by Parent-THC Saliva Testing
Parent THC was often absent from oral fluid despite repeated supervised swallowed THC doses. In this study, the metabolite THCCOOH was detected much more consistently, showing why a saliva result depends on the analyte and administration route.
Supervised dosing did not guarantee parent-THC detection
Ten male daily cannabis users received 37 supervised 20-mg dronabinol doses across an escalating dosing schedule. Researchers collected 440 oral-fluid specimens over nine days. Participants had smoked cannabis before admission, making baseline residual exposure important.
This was a pharmacokinetic study, not a study validating a roadside impairment threshold. The collection device and the laboratory’s quantification limits were part of the observed detection pattern.
The metabolite and parent drug behaved differently
THCCOOH was detected in 432 specimens, or 98.2%. Parent THC was detected in 20.7%, with the highest concentrations generally near admission rather than after repeated oral dosing. The active metabolite 11-OH-THC was not identified at the method’s oral-fluid quantification limit.
These percentages describe specimens, not independent people. Repeated samples from the same ten participants cannot be presented as a 440-person validation study.
The comparison also depends on analytical sensitivity
The method measured THCCOOH at much lower concentrations than parent THC. Therefore, the difference in positivity cannot be attributed exclusively to biological distribution. The authors specifically recognized the role of differing quantification limits.
Oral capsules also do not deposit THC directly into the mouth in the way smoke or an oromucosal spray can. Parent THC remaining from earlier smoking and a metabolite increasing during swallowed dosing can consequently follow different time courses.
A negative saliva result has a limited meaning
A negative parent-THC result under this method did not establish noncompliance with observed oral dosing. Conversely, a positive THCCOOH result did not establish current impairment, a precise dose or a particular time of smoking.
The sample was small, entirely male and composed of daily users receiving a high supervised regimen. The findings should not be turned into a detection timetable for an occasional edible consumer or a different saliva device.
For the separate forensic question, see our discussion of cannabinoid concentrations and evidence of impairment.
Primary research
Disposition of Cannabinoids in Oral Fluid after Controlled Around-the-Clock Oral THC Administration. Clinical chemistry (2010). DOI: 10.1373/clinchem.2009.141853.
