Subjective drug effects are not reliable chemical identification. In a controlled comparison, participants had difficulty distinguishing orally administered methamphetamine from MDMA even though the drugs produced some different effects.
Kirkpatrick and colleagues studied 11 adults during a 13-day residential experiment. Participants received oral methamphetamine at 20 or 40 mg, MDMA at 100 mg, and placebo in separate blocks. Investigators assessed plasma drug concentrations, cardiovascular responses, subjective effects and cognitive performance, as well as food intake and sleep.
Using the same people across conditions reduced some between-person variability. It did not make the doses equivalent in every pharmacological respect, and only the oral route was tested.
Both drugs increased cardiovascular measures and positive subjective effects and reduced food intake. Participants nevertheless had difficulty identifying which amphetamine they had received. Methamphetamine improved selected performance measures and disrupted sleep, whereas MDMA increased negative subjective-effect ratings. Few residual effects were detected under this protocol.
The important distinction is between overlap and identity. Similar reported stimulation does not establish identical composition, dose, pharmacokinetics or functional consequences.
An account that a substance “felt like” a particular stimulant cannot replace chemical analysis. In this experiment, plasma assays and known administered drugs supplied information that subjective identification could not. The findings do not establish how accurately an experienced user could identify an unknown street preparation, especially one containing multiple substances.
The small sample, chosen doses, residential conditions and oral administration constrain generalization. The study also was not designed to estimate a diagnostic accuracy for real-world drug identification.
A person’s impression of an ingested substance does not determine impairment, and these laboratory responses do not establish a driving threshold. A defensible interpretation identifies the actual analytes and specimen, then separately evaluates the person’s behavior and circumstances.
Related reading: What a controlled driving study can establish.