An evaluation of the sensitivity of the Standardised Field Sobriety Tests (SFSTs) to detect impairment due to marijuana intoxication

Abstract

The Standardised Field Sobriety Tests (SFST) were developed to test for alcohol intoxication but are currently being used by the State Police of Victoria (Australia) to test for driving impairment associated with drugs other than alcohol. The aim of the present study was to assess whether the SFSTs provide a sensitive measure of impairment following the consumption of a drug other than alcohol: delta-9-tetrahydrocannabinol (THC or cannabis). In a repeated-measures design, 40 participants consumed cigarettes that contained either 0% THC (placebo), 1.74% THC (low dose) or 2.93% THC (high dose). For each condition, after smoking a cigarette, participants performed the SFSTs on three occasions: 5 min (Time 1), 55 min (Time 2) and 105 min (Time 3) after the smoking procedure had been completed. The results revealed that there was a positive relationship between the dose of THC administered and the number of participants classified as impaired based on the SFSTs. Results also revealed that the percentage of participants classified as impaired decreased from Time 1 to Time 3 and that the addition of a new sign, head movements or jerks (HMJ), increased the percentage of participants classified as impaired in both the low and high THC conditions. These findings suggest that impaired performance on the SFSTs is positively related to the dose of THC administered and that the inclusion of HMJ as a scored sign in the SFSTs improves their predictive validity when testing for THC intoxication.

The relationship between performance on the standardised field sobriety tests, driving performance and the level of Δ9-tetrahydrocannabinol (THC) in blood

“…The consumption of THC has also been found to impair performance on the SFSTs [14]. Furthermore, the drug evaluation and classification program (DECP) (a 12 step testing program that includes the administration of the SFSTs) has previously been found to reliably indicate whether individuals have consumed drugs other than alcohol [15,16].…”

“…The additional sign, head movements or jerks (HMJ) during performance of the horizontal gaze nystagmus (HGN) test, is not traditionally included in the SFST scoring procedure but is considered to be a possible symptom of drug use [8]. Inclusion of HMJ has previously been shown to increase the number of subjects classified as impaired on the SFSTs following the consumption of THC [14].…”

The relationship between observed signs of impairment and THC concentration in oral fluid

“…The low sensitivity of tests for impairment due to cannabis based on the observation of signs was reported previously (Tzambazis and Stough, 2002;Papafotiou et al, 2005a). Most studies have been controlled experimental studies or were carried out with drivers apprehended on suspicion of DUI of drugs .…”

“…The low sensitivity of the observational sign test in detecting cannabis use has been previously reported (Papafotiou et al, 2005a(Papafotiou et al, , 2005b; as has the possibility of improving the sensitivity when the test is supplemented with two questions about recent drug use (Mathijssen and Sjoerd, 2005). However, we had no reliable information about a subject's intake of cannabis; neither the dose nor the time was known, and the influence of possible effects due to tolerance is uncertain.…”

“…However, various countries use these types of performance-based tests to detect impairment associated with drugs other than alcohol (Raes et al, 2008). In order to increase the sensitivity of SFSTs for THC, the addition of some tests and observations has been suggested, such as "head movements or jerks" (Papafotiou et al, 2005a(Papafotiou et al, , 2005b or a series of observations conducted by the physician as part of the Norwegian clinical test of impairment . Even with these extra observations, however, THC impairment is difficult to detect, particularly at lower THC concentrations (Bosker et al, 2012).…”