Pooling a 3.9-Centimeter Hair Segment Did Not Produce Month-by-Month Cannabis Results

The hair study combined material from the proximal segment for analysis. It did not separately measure a cannabinoid concentration for each month represented along the hair shaft.

The preparation homogenized a segment

Investigators selected the first 3.9 centimeters nearest the scalp, cut the hair into short pieces and mixed it before taking an analytical portion. The paper used that segment as an approximate retrospective exposure window. The result was an aggregate measurement of the prepared material.

Pooling removes position-specific information

Once pieces from across the segment are mixed, the final concentration does not retain a separate value for each original position. A positive pooled result cannot identify which small subsection contained the analyte, and a negative result cannot establish that every subsection was independently tested and negative.

An approximate window is not an exact calendar

The authors noted practical problems aligning some short strands. Biological growth and incorporation add further limitations to precise timing. The pooled concentration therefore cannot be divided into monthly doses or used to assign a specific consumption date. A claim about a temporal sequence would require an appropriately collected and analyzed segmental dataset, together with its own assumptions. This study’s aggregate hair findings were evidence about detection under a defined preparation, not a detailed calendar of cannabis use.

Related analysis: the study’s broader findings and limitations.

Research cited

Huestis and colleagues (2006). Cannabinoid Concentrations in Hair from Documented Cannabis Users.