Expired Carbon Monoxide Distinguished Cannabis Routes Without Measuring Impairment
Expired carbon monoxide can reflect combustion-related exposure without measuring the degree of cannabis impairment. A route-comparison study found more expired carbon monoxide after smoked cannabis than after vaporized cannabis.
Three routes and a placebo comparison
The study examined frequent and occasional users after smoked, vaporized and oral cannabis and placebo. Researchers recorded subjective responses, cardiovascular changes and expired carbon monoxide. These are different outcomes rather than interchangeable measures of intoxication.
Subjective and physiological patterns differed
Smoking and vaporization increased subjective ratings in both use groups. After oral dosing, significant subjective effects were reported in occasional users but not the same way in frequent users. Heart-rate changes did not show corresponding group differences in the reported comparisons.
The carbon-monoxide result had a specific interpretation
Smoking increased expired carbon monoxide compared with vaporization over the reported post-dose period. This supports a route-related difference in exposure to a combustion product. It does not prove that vaporized cannabis lacked intoxicating effects or was safe for driving.
Expired carbon monoxide is not THC in whole blood, plasma, saliva or breath aerosol. A low value cannot establish absence of cannabis use across all routes. Conversely, subjective adaptation does not mean cardiovascular responses have disappeared. A forensic interpretation should specify the analyte, collection method, administration route and actual functional observations rather than treating one respiratory measurement as a universal cannabis test.
Related: interpreting cannabis tolerance claims.
Research cited
Newmeyer MN; Swortwood MJ; Abulseoud OA; Huestis MA. Subjective and physiological effects, and expired carbon monoxide concentrations in frequent and occasional cannabis smokers following smoked, vaporized, and oral cannabis administration. Drug and alcohol dependence (2017). doi:10.1016/j.drugalcdep.2017.02.003. Findings discussed from the study abstract.
