Controlled Cannabis Vaporizer Administration: Blood and Plasma Cannabinoids with and without Alcohol

Clin Chem. 2015 Jun;61(6):850-69. doi: 10.1373/clinchem.2015.238287. Epub 2015 May 27.


Background: Increased medical and legal cannabis intake is accompanied by greater use of cannabis vaporization and more cases of driving under the influence of cannabis. Although simultaneous Δ(9)-tetrahydrocannabinol (THC) and alcohol use is frequent, potential pharmacokinetic interactions are poorly understood. Here we studied blood and plasma vaporized cannabinoid disposition, with and without simultaneous oral low-dose alcohol.

Methods: Thirty-two adult cannabis smokers (≥1 time/3 months, ≤3 days/week) drank placebo or low-dose alcohol (target approximately 0.065% peak breath-alcohol concentration) 10 min before inhaling 500 mg placebo, low-dose (2.9%) THC, or high-dose (6.7%) THC vaporized cannabis (6 within-individual alcohol-cannabis combinations). Blood and plasma were obtained before and up to 8.3 h after ingestion.

Results: Nineteen participants completed all sessions. Median (range) maximum blood concentrations (Cmax) for low and high THC doses (no alcohol) were 32.7 (11.4-66.2) and 42.2 (15.2-137) μg/L THC, respectively, and 2.8 (0-9.1) and 5.0 (0-14.2) μg/L 11-OH-THC. With alcohol, low and high dose Cmax values were 35.3 (13.0-71.4) and 67.5 (18.1-210) μg/L THC and 3.7 (1.4-6.0) and 6.0 (0-23.3) μg/L 11-OH-THC, significantly higher than without alcohol. With a THC detection cutoff of ≥1 μg/L, ≥16.7% of participants remained positive 8.3 h postdose, whereas ≤21.1% were positive by 2.3 h with a cutoff of ≥5 μg/L.

Conclusions: Vaporization is an effective THC delivery route. The significantly higher blood THC and 11-OH-THC Cmax values with alcohol possibly explain increased performance impairment observed from cannabis-alcohol combinations. Chosen driving-related THC cutoffs should be considered carefully to best reflect performance impairment windows. Our results will help facilitate forensic interpretation and inform the debate on drugged driving legislation.

Publication types

  • Controlled Clinical Trial
  • Research Support, N.I.H., Intramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Administration, Oral
  • Adult
  • Cannabinoids / blood*
  • Cannabinoids / pharmacokinetics
  • Dronabinol / administration & dosage
  • Dronabinol / analogs & derivatives
  • Dronabinol / blood
  • Ethanol / administration & dosage*
  • Female
  • Humans
  • Male
  • Marijuana Smoking / blood
  • Medical Marijuana / administration & dosage*
  • Medical Marijuana / blood
  • Nebulizers and Vaporizers
  • Young Adult


  • Cannabinoids
  • Medical Marijuana
  • 11-hydroxy-delta(9)-tetrahydrocannabinol
  • Ethanol
  • Dronabinol