Detection time for THC in oral fluid after frequent cannabis smoking

The use of oral fluid for detecting drugs of abuse has become increasingly more frequent. Few studies have, however, investigated the detection times for drugs of abuse in oral fluid, compared with that of in urine or in blood. Cannabis is the world's most widely used drug of abuse, and the detection times for cannabis, in different types of matrixes, are therefore important information to the laboratories or institutions performing and evaluating drugs of abuse analyses. It is well known that frequent use of high dosages of cannabis, for longer periods of time, might lead to prolonged detection times for THC-COOH in urine. Cannabis intake is detected in oral fluid as THC, and a positive finding is considered to be a result of recent smoking, although some studies have already reported longer detection times. The aim of this study was to investigate the detection time for THC in oral fluid, collected from drug addicts admitted for detoxification. Findings in oral fluid were compared with findings in urine, among 26 patients admitted to a closed detoxification unit.

The study, being the first in doing so, describes the concentration-time profiles for THC in oral fluid among chronic cannabis users, during monitored abstinence, using the Intercept collection kit. The study also includes the concentration-time profiles for creatinine-corrected THC-COOH ratios in urine samples, included to monitor for the possibility of new intakes.

THC was detected in oral fluid collected from 11 of the 26 patients in the study. The elimination curves for THC in oral fluid revealed that negative samples could be interspersed among positive samples several days after cessation, whereas the THC-COOH concentrations in urine were decreasing. THC was, in this study, detected in oral fluid for up to 8 days after admission.

The study shows that frequent use of high dosages of cannabis may lead to prolonged detection times, and that positive samples can be interspersed among negative samples. These results are of great importance when THC results from oral fluid analyses are to be interpreted.