A meta-analysis published in Heliyon revealed that oral fluid (OF) tests do not provide accurate indications of when individuals last used cannabis or the substance’s intoxicating effects. Researchers from the Canadian Institute for Substance Use Research at the University of Victoria in British Columbia noted that OF tests often produce disparate results even when subjects use similar cannabis amounts. They concluded that OF tests do not offer valid measures of intoxication.
The research team analyzed published empirical articles from two databases (PubMed and Scopus) that included 116 subjects. These studies documented the administration of cannabis to subjects in a controlled setting in which OF tests showed precise tetrahydrocannabinol (THC) concentrations in OF for each subject for at least two different time points after cannabis consumption using confirmatory methods.
The analysis suggested that oral fluid testing may not provide the most accurate readings. The high degree of variability in THC concentrations for subjects given the same amount of cannabis indicates that OF testing may not be as reliable as test users believe. The researchers noted that this variability resulted in some very high outliers in terms of THC concentrations.
The analysis suggested that subjects who inhale cannabis are far more likely to test positive on oral fluid tests when compared to individuals who consume cannabis-infused products such as edibles and beverages. Some subjects can test positive for previous cannabis exposure for more than 24 hours after smoking, even if intoxication effects have decreased.
Analysis of blood, urine, and hair samples is commonly used as part of employment screening practices, and oral fluid testing has generally been used after a traffic or workplace accident to determine recent substance use. Saliva samples used in oral fluid drug testing practices may help determine intoxication levels and recency of use. However, the researchers questioned OF test validity for detection of prior use or impairment.
