In a controlled study, oral cannabis (brownies) produced blood THC levels far lower than inhalation, with peak effects at 1.5-3 hours, effects lasting 6-8 hours, and blood cannabinoid levels correlating with subjective drug effects.
Readers who consume edible cannabis and want to understand its pharmacokinetic profile.
Oral cannabis: peak blood THC only 1-3.5 ng/mL, but impairment lasted 6-8 hours
What the researchers found
Six healthy adults per dose received cannabis brownies containing 10, 25, or 50 mg THC, with specimens collected for 9 days.
Blood THC concentrations were remarkably low: mean peak levels were only 1, 3.5, and 3.3 ng/mL for the three doses, far lower than levels seen after smoking. Oral fluid THC concentrations peaked immediately after eating (from residue in the mouth, not systemic absorption).
Subjective drug effects and cognitive impairment were dose-dependent, peaked at 1.5-3 hours, and lasted 6-8 hours. Whole blood cannabinoid levels correlated significantly with subjective drug effects, but oral fluid levels did not reliably predict impairment.
The THC detection window in blood was 0-22 hours and in oral fluid was 1.9-22 hours. The 11-OH-THC metabolite had concentrations similar to THC itself, and the THCCOOH metabolite had higher concentrations and longer detection times.
Why it matters
Most cannabis pharmacokinetic research has studied smoking. As edibles grow in market share, understanding their unique profile is critical. The low blood THC levels from oral cannabis complicate drug testing: a person may be significantly impaired (effects lasting 6-8 hours) while having blood THC below per se legal limits designed for smoked cannabis.
The numbers in context
Doses: 10, 25, 50 mg THC brownies. Peak blood THC: 1, 3.5, 3.3 ng/mL. Peak effects: 1.5-3 hours. Duration: 6-8 hours. Detection window (blood): 0-22 hours. Detection window (oral fluid): 1.9-22 hours. Blood levels correlated with subjective effects. Oral fluid levels did not predict impairment.
How the study worked
Controlled pharmacokinetic study with 18 healthy adults (6 per dose). Cannabis brownies at 10, 25, or 50 mg THC. Blood and oral fluid specimens collected at baseline and for 9 days (6 days inpatient, 3 outpatient). Subjective effects, cardiovascular measures, and cognitive performance assessed for 8 hours.
What this study cannot tell us
Small sample (6 per dose). Only one cannabis product tested (brownies). The 50 mg dose did not produce higher peak THC than the 25 mg dose, possibly due to variable absorption. Individual variation in oral absorption is well-known. The study used healthy adults without tolerance, who may respond differently than regular users.
How to read the evidence
Strong evidence from a controlled pharmacokinetic study with detailed multi-day specimen collection.
When this study was published
Published in 2017. Foundational pharmacokinetic data for edible cannabis.
The bigger picture
This study has direct implications for cannabis-impaired driving laws. Per se THC limits in blood (like Colorado's 5 ng/mL) were designed based on smoking pharmacokinetics. Edible users may never reach these thresholds yet still be impaired for 6-8 hours. Conversely, oral fluid roadside tests may detect recent eating but cannot reliably indicate impairment level.
Questions still open
- Should per se THC driving limits be different for edible versus smoked cannabis? Could oral fluid testing protocols be modified to better detect edible cannabis impairment? Why did the 50 mg dose not produce higher blood levels than the 25 mg dose?
Common questions
How long do edible cannabis effects last?
Can a blood test tell if you are impaired from edibles?
Read the original research
Pharmacokinetic Profile of Oral Cannabis in Humans: Blood and Oral Fluid Disposition and Relation to Pharmacodynamic Outcomes.
Journal of analytical toxicology, 41(2), 83-99
Citation
Vandrey, Ryan; Herrmann, Evan S; Mitchell, John M; Bigelow, George E; Flegel, Ronald; LoDico, Charles; Cone, Edward J. (2017). Pharmacokinetic Profile of Oral Cannabis in Humans: Blood and Oral Fluid Disposition and Relation to Pharmacodynamic Outcomes.. Journal of analytical toxicology, 41(2), 83-99. https://doi.org/10.1093/jat/bkx012