A placebo-controlled study of racemic d,l-methamphetamine found no statistically significant overall driving difference under its experimental conditions. That finding should retain its formulation and should not be treated as a direct head-to-head comparison with pure d-methamphetamine.
Silber and colleagues studied 20 recreational stimulant users who received oral d,l-methamphetamine at 0.42 mg/kg and placebo in a counterbalanced double-blind crossover design. Driving was assessed approximately 2.5 hours after administration. This was controlled human primary research, not a naturalistic user cohort or an animal experiment.
Overall weighted driving-error scores averaged 125.4 with d,l-methamphetamine and 117.3 with placebo; the reported comparison was p = 0.10. Some braking and speed measures showed trend-level differences, but did not meet the conventional significance criterion. These observations cannot be converted into demonstrated global impairment or proof of equivalence.
The detailed results report mean methamphetamine concentrations in blood and saliva of 90 and 343 ng/mL at 120 minutes, 95 and 475 at 170 minutes, and 105 and 568 at 240 minutes. These are group means in separate matrices, not individual impairment cutoffs. The abstract rounds or describes some sampling values differently, and the discussion contains inconsistent concentration wording. The detailed results should be identified explicitly rather than silently mixing numbers from different sections.
A separate d-methamphetamine study involved a different sample and results. Neither experiment randomized participants between the two formulations within one head-to-head comparison. Comparing their means cannot establish a reliable potency ratio, safer formulation or isomer-specific legal limit. Small samples, one oral dose and brief simulator tasks also limit generalization to repeated use and actual traffic. A forensic opinion must identify the administered formulation and distinguish it from what an evidentiary assay actually resolved.
Compare these findings with our account of the controlled d-methamphetamine driving study. The design and measured outcome determine which conclusions can be carried into an individual case.
Original investigation: doi:10.1007/s00213-011-2437-7.