Equal Nominal THC Doses Produced Stronger Effects With Vaporization in Infrequent Users

The same amount of THC in the study material did not produce the same exposure or effects when cannabis was smoked versus vaporized. In a controlled crossover trial, vaporization generally delivered stronger effects in adults who had not recently used cannabis.

A fixed-dose human comparison

Seventeen healthy adults completed six sessions involving smoked or vaporized cannabis containing 0, 10 or 25 mg THC. Participants reported no cannabis use in the preceding month. Doses were randomized within inhalation-method blocks, with the order of those blocks counterbalanced.

The study used plant material and a particular vaporizer procedure. Participants could recognize whether they were smoking or vaporizing; the design did not make the administration route invisible.

Product dose and delivered dose are different

At 25 mg, mean peak whole-blood THC was approximately 14.4 ng/mL after vaporization and 10.2 ng/mL after smoking. Some subjective and performance effects were also stronger after vaporization. The finding supports a route-dependent delivery difference under the tested conditions, rather than a universal equivalence between milligrams in a product and milligrams reaching circulation.

The performance pattern was not uniform. For example, vaporized conditions affected several digit-symbol outcomes, while not every smoked condition or task comparison reached significance. Reporting only the strongest result would exaggerate the consistency of the effects.

Blood and performance followed different clocks

Whole-blood THC declined faster than several subjective and cognitive effects. Some performance effects persisted after THC fell below the assay’s quantification limit. That observation makes a low later concentration an incomplete description of the earlier exposure course.

It also does not establish that every participant remained impaired for a fixed number of hours. This experiment measured laboratory tasks, subjective ratings and physiological outcomes rather than actual crash risk.

Limits of generalization

The sample was small and consisted of infrequent users. One vaporizer configuration, a limited dose range and one principal cannabis composition were tested. These findings cannot establish a dose conversion for all vaporizers, concentrates or daily users. The paper’s published correction concerned the table title; its table describes peak changes from baseline, not a single simultaneous measurement of every outcome.

For the separate forensic question, see our discussion of cannabinoid concentrations and evidence of impairment.

Primary research

Acute Effects of Smoked and Vaporized Cannabis in Healthy Adults Who Infrequently Use Cannabis: A Crossover Trial. JAMA Network Open (2018). DOI: 10.1001/jamanetworkopen.2018.4841.

Published correction to the table title.