Standardized field sobriety tests did not significantly distinguish d-methamphetamine from placebo in a controlled study of 58 recreational drug users. That result concerns the sensitivity of specific tests under defined conditions. It does not prove that every participant was safe to drive.
Downey and colleagues used a double-blind, within-subject, counterbalanced, placebo-controlled design. Participants received oral d-methamphetamine at 0.42 mg/kg, MDMA at 100 mg, and placebo in separate conditions. Examiners administered horizontal gaze nystagmus, walk-and-turn and one-leg-stand tests four and 25 hours after treatment. Head movements or jerks were also evaluated.
This was controlled human primary research, not a roadside case series or a validation of all components of a drug recognition examination. The methamphetamine and MDMA conditions were separate treatments, not a combined dose.
Methamphetamine did not significantly impair the individual or overall SFST results relative to placebo. At four hours, the overall SFST classification identified three methamphetamine participants as impaired, compared with two under placebo. Adding head movements or jerks increased the methamphetamine count to four, without establishing a significant drug-placebo distinction.
MDMA produced significant SFST impairment relative to placebo. At four hours, ten participants met the overall SFST classification; incorporating head movements or jerks increased the count to 13, approximately 22% of 58. Reporting the latter percentage without identifying the augmented test would obscure the method. No significant treatment differences were observed at 25 hours.
The administered compound was d-methamphetamine. SFST performance is a behavioral outcome, not a quantitative blood or oral-fluid assay, and does not identify an analyte or its concentration. Failure to detect an exposure through these tests cannot establish that the exposure was absent. Conversely, a failed test alone does not identify which substance caused it.
The defensible use is to question categorical claims that this test battery reliably detects every methamphetamine exposure. Its limits include the selected recreational-user sample, one dose, oral administration and two assessment times. The experiment does not determine performance after high repeated doses, sleep deprivation or mixtures, and it does not supply a universal roadside diagnostic accuracy estimate.
For the distinction between behavioral testing and simulated driving, see our controlled driving-study analysis. Neither a normal SFST nor a positive drug result alone reconstructs an individual’s actual driving.
Read the original investigation: doi:10.1016/j.forsciint.2012.02.025.