Oral THCA-A Exposure Did Not Produce Detectable Hair THCA-A in One Volunteer

In a small controlled experiment, one volunteer took oral THCA-A repeatedly without producing detectable THCA-A in the sampled hair or sebum/sweat. That finding questions a simple assumption that systemic exposure necessarily yields a positive hair result for the same cannabinoid.

This experiment tested the plant acid

Moosmann and colleagues reported a volunteer receiving 50 mg THCA-A daily for 30 days. THCA-A is the acidic plant precursor of THC; it is not the same analyte as THC or the metabolite THC-COOH.

The researchers reported no detectable THCA-A in the segmented hair specimens or the collected sebum/sweat samples. Their interpretation concerned routes of incorporation into hair, rather than whether the volunteer had taken the administered substance.

A negative hair result did not erase known exposure

The administration history was controlled. The nondetection therefore illustrated a limitation of using that hair analyte as a necessary marker of systemic uptake under the tested conditions. Different specimens and analytes do not have to become positive together.

The investigators interpreted their work as supporting external contamination as an important explanation for THCA-A in forensic hair samples, including transfer from handling plant material. That interpretation does not establish the route of entry in every individual positive sample.

One participant cannot define every exposure

The THCA-A experiment involved one person, one oral regimen and particular collection and analytical procedures. It cannot establish that systemic incorporation is impossible at every dose, by every route or in every person.

For interpretation, identify the specific cannabinoid and the specimen before making an exposure claim. This question is distinct from dating THC-COOH in older hair segments: here, the relevant result was nondetection of the administered plant acid. Neither result measures impairment at a particular event.

Related: Why older hair segments complicate THC-COOH dating.

Research cited

Moosmann B; Roth N; Auwärter V. Scientific Reports (2015), 5:14906. Finding cannabinoids in hair does not prove cannabis consumption.