Blood and Saliva Showed Different Patterns When Cannabis Was Smoked or Vaporized

Saliva THC did not mirror the blood exposure difference between smoked and vaporized cannabis in a controlled human study. The finding matters when someone treats a high oral-fluid result as evidence of greater absorbed dose.

The same participants completed both routes

Seventeen healthy adults who had not used cannabis in the previous month completed six sessions: smoked or vaporized cannabis containing 0, 10 or 25 mg THC. Researchers collected venous whole blood and oral fluid before dosing and through eight hours afterward.

This pharmacokinetic report came from the same experiment as a companion report on subjective and performance effects. The publications provide different analyses of one cohort, rather than independent replications.

A route difference in blood was not reproduced in saliva

At the 25 mg dose, mean maximum whole-blood THC concentrations were 10.24 ng/mL after smoking and 14.36 ng/mL after vaporization. The corresponding mean oral-fluid peaks were approximately 496 and 506 ng/mL. Similar saliva means do not prove formal equivalence; they show that the larger systemic exposure with vaporization was not reflected by a comparable saliva increase.

Oral-fluid THC was often detectable after whole-blood THC was no longer quantifiable. Oral-fluid THC-COOH detection was irregular and sometimes absent. The authors considered deposition in the mouth an important explanation for why oral-fluid profiles differed from systemic profiles.

Sampling and apparatus limit the inference

The first post-dose collection occurred ten minutes after administration ended, so these measured maxima need not capture the earliest physiological peak. The study used a particular plant preparation, pipe and balloon vaporizer, with vaporization at a fixed temperature. It did not validate the same relationship for every cartridge, concentrate or inhalation pattern.

Associations with cognitive and psychomotor outcomes were at best moderate and often nonsignificant. The useful inference is matrix-specific: blood and saliva can respond differently to a route comparison. Neither the oral-fluid number nor a cross-study comparison of peaks supplies a universal impairment classification.

Related: interpreting THC concentrations separately from impairment.

Primary research

Acute Pharmacokinetic Profile of Smoked and Vaporized Cannabis in Human Blood and Oral Fluid. DOI: 10.1093/jat/bky104.