Eating Cannabis Produces Much Lower Blood THC Levels Than Smoking, with Effects Peaking at 1.5-3 Hours and Lasting 6-8 Hours
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.
Quick Facts
What This Study 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.
Key Numbers
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 They Did This
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.
Why This Research 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 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.
What This Study Doesn't 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.
Questions This Raises
- ?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?
Trust & Context
- Key Stat:
- Oral cannabis: peak blood THC only 1-3.5 ng/mL, but impairment lasted 6-8 hours
- Evidence Grade:
- Strong evidence from a controlled pharmacokinetic study with detailed multi-day specimen collection.
- Study Age:
- Published in 2017. Foundational pharmacokinetic data for edible cannabis.
- Original Title:
- Pharmacokinetic Profile of Oral Cannabis in Humans: Blood and Oral Fluid Disposition and Relation to Pharmacodynamic Outcomes.
- Published In:
- Journal of analytical toxicology, 41(2), 83-99 (2017)
- Authors:
- Vandrey, Ryan(49), Herrmann, Evan S(10), Mitchell, John M(7), Bigelow, George E, Flegel, Ronald, LoDico, Charles, Cone, Edward J
- Database ID:
- RTHC-01543
Evidence Hierarchy
Enrolls participants and follows them forward in time.
What do these levels mean? →Frequently Asked Questions
How long do edible cannabis effects last?
In this controlled study, effects from cannabis brownies (10-50 mg THC) peaked at 1.5-3 hours and lasted 6-8 hours. This is longer than smoked cannabis, which typically peaks within minutes and lasts 2-4 hours.
Can a blood test tell if you are impaired from edibles?
Blood THC levels from edibles were surprisingly low in this study (1-3.5 ng/mL peak), potentially below legal per se limits, even while participants were experiencing significant subjective effects and cognitive impairment. This means blood tests may underestimate impairment from edible cannabis.
Read More on RethinkTHC
Cite This Study
https://rethinkthc.com/research/RTHC-01543APA
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
MLA
Vandrey, Ryan, et al. "Pharmacokinetic Profile of Oral Cannabis in Humans: Blood and Oral Fluid Disposition and Relation to Pharmacodynamic Outcomes.." Journal of analytical toxicology, 2017. https://doi.org/10.1093/jat/bkx012
RethinkTHC
RethinkTHC Research Database. "Pharmacokinetic Profile of Oral Cannabis in Humans: Blood an..." RTHC-01543. Retrieved from https://rethinkthc.com/research/vandrey-2017-pharmacokinetic-profile-of-oral
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkTHC research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.