Trace THC in Plasma but Not Urine: Findings After a Commercial CBD Oil
A controlled CBD-oil study detected low parent THC in some plasma samples while finding no parent THC in urine. THC-COOH was present in urine. These results concern different analytes and specimens, so their apparent disagreement is not inherently a testing failure.
The product already contained THC
Ten healthy volunteers used a commercial hemp-extract oil daily. The measured daily exposure was approximately 6.61 mg CBD and 0.28 mg THC. Samples were collected on day five: plasma before dosing and up to three hours afterward, with morning and postdose urine.
This was exposure to a mixed product containing trace THC, not a trial of chemically pure CBD. The findings therefore cannot be used to prove that CBD converted into THC inside the participants.
Parent drug and carboxy metabolite behaved differently
Low THC concentrations were quantified in some postdose plasma samples, while others were below quantification or not detected. Parent THC was not detected in the collected urine samples. By contrast, THC-COOH was found in participants’ urine, including morning samples before that day’s dose.
A morning sample on the fifth treatment day was not a drug-free pretreatment baseline: participants had already received previous daily doses. The sampling design supports persistence across the dosing interval under these conditions, rather than a new-use time stamp for every positive metabolite result.
Why a “THC test” needs an analyte name
The assay used gas chromatography–mass spectrometry with a reported quantification limit of 0.20 ng/mL for the targeted compounds. A result below that level is distinct from a reliably quantified concentration. “Not detected” also describes the specified method and specimen, not the absence of exposure at all times.
Urine procedures included hydrolysis, and urinary THC-COOH cannot be numerically substituted for parent THC in plasma. Calling both a “THC level” obscures the distinction between parent compound and metabolite, as well as the specimen and preparation.
Exposure was demonstrated; impairment was not measured
The study did not test driving performance or establish that its low plasma concentrations caused functional impairment. It also did not validate a rule that separates prescribed products from other cannabis sources using an isolated metabolite result.
Its small sample, single formulation and short postdose sampling window limit generalization. In a disputed CBD-product case, the product’s actual composition, dosing history, specimen timing and confirmed analyte are more informative than relying on the word “CBD” on a label. The paper demonstrates a plausible documented exposure source under defined conditions, rather than an automatic explanation for every positive result.
Related analysis: Concentration Is Not Impairment: THC Blood Levels in California Driving Cases.
Primary research
Ioannis Papoutsis and colleagues. Determination of Δ9-tetrahydrocannabinol, 11-nor-carboxy-Δ9-tetrahydrocannabinol and cannabidiol in human plasma and urine after a commercial cannabidiol oil product intake. Forensic Toxicology (2024). DOI: 10.1007/s11419-024-00686-0.
