A laboratory identification of methamphetamine does not necessarily identify its source. Chiral testing asks an additional question: which mirror-image form, or mixture of forms, is present?
Chemical identity and stereochemistry
Barry Logan’s 2002 forensic review distinguishes the d- and l-forms of methamphetamine and explains that stereochemistry affects pharmacological activity. An assay reporting total methamphetamine may not resolve those forms. The laboratory must use an appropriate stereospecific method if the distinction is important.
A confirmed total-drug result and a resolved isomer result answer different analytical questions. Neither should be described as if it necessarily supplies the other.
Medication-related explanations require specific evidence
The review discusses several pathways by which medicines can produce amphetamine-related findings. It describes selegiline metabolism to l-methamphetamine and l-amphetamine, and benzphetamine metabolism that can yield d-methamphetamine and amphetamine. These examples show why finding the d-form alone does not uniquely identify an illicit supply.
Logan also discusses historical decongestant preparations containing l-methamphetamine. That discussion concerns products and evidence available in 2002; it is not a statement about every currently sold inhaler or its formulation.
What to request from the laboratory
A useful evaluation identifies the specimen, confirmed analytes, concentrations, reporting limits and whether chiral separation was performed. If percentages are reported, the interpretation should consider quantification near the reporting limits and the validation of the specific method.
Medication records and timing can then be compared with the chemistry. Where a parent medicine or a more specific metabolite can distinguish explanations, those additional measurements may be more informative than an isomer label by itself. An untested alternative remains an alternative, rather than a demonstrated explanation.
Source attribution is separate from impairment
Even a well-supported source opinion does not establish the degree of functional impairment at an earlier event. That requires additional evidence about exposure history, observations and timing. Conversely, a lawful source does not itself establish unimpaired performance.
The defensible conclusion is conditional: stereochemistry can narrow a source assessment, but a particular isomer pattern must be interpreted with the complete analytical and medication record.
Scientific source
Logan BK. Methamphetamine—Effects on Human Performance and Behavior. Forensic Science Review. 2002;14(1–2):133–151. This article analyzes the supplied historical review; studies discussed within that review are secondary-source evidence here.
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