Cannabis use introduces various compounds into the body, with delta-9-tetrahydrocannabinol (THC) being the primary psychoactive component. Once consumed, the body breaks down and eliminates these compounds. This metabolic process generates byproducts, one of which is Carboxy-THC. This metabolite serves as an important indicator of past cannabis exposure and is often the focus of drug tests due to its stability and prolonged presence in the body.
Understanding Carboxy-THC
When THC enters the body, it undergoes a metabolic process primarily in the liver. Liver enzymes convert THC into other molecules.
One of the first metabolites formed is 11-hydroxy-THC (11-OH-THC), which is also psychoactive and contributes to the effects of cannabis. This 11-OH-THC is then further oxidized by liver enzymes into 11-nor-9-carboxy-THC, commonly known as Carboxy-THC or THC-COOH. Unlike its predecessors, Carboxy-THC is not psychoactive and does not produce intoxicating effects. Its stability and tendency to be stored in fat cells make it a reliable and long-lasting marker for cannabis use.
How Carboxy-THC Levels Are Assessed
Carboxy-THC levels in biological samples are primarily assessed through various testing methods, with urine tests being the most common. Blood and hair samples are also used. Initial screening tests often use immunoassays to detect cannabinoids, including Carboxy-THC.
If an initial screen is positive, a confirmatory test using more precise methods like gas chromatography-mass spectrometry (GC-MS) or liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) is performed. These tests specifically identify and quantify Carboxy-THC. Regulatory bodies establish standard cutoff levels to differentiate between actual use and environmental exposure, such as secondhand smoke. For urine tests, a common initial screening cutoff for cannabinoids is 50 ng/mL, while the confirmatory cutoff for Carboxy-THC is 15 ng/mL. Hair tests have much lower cutoff concentrations, often in picograms per milligram (pg/mg), such as 0.1 pg/mg for Carboxy-THC. A “high level” means the concentration of Carboxy-THC in the sample exceeds these established thresholds.
Factors Influencing Carboxy-THC Levels
Several factors influence the concentration of Carboxy-THC in an individual’s body and how long it remains detectable. The frequency and dosage of cannabis use are significant; heavier and more frequent use leads to higher and more prolonged detectable levels. For instance, chronic users may have detectable levels for up to 30 to 60 days after cessation.
Individual metabolism rates also play a role, as some people process substances more quickly. Body fat percentage is another influencing factor because THC and its metabolites, including Carboxy-THC, are lipid-soluble and accumulate in fat tissues. Individuals with higher body fat may retain Carboxy-THC for longer periods. Hydration status can also impact urine concentrations, with dilute urine potentially leading to lower Carboxy-THC levels. The route of administration, whether inhaled or ingested, affects how THC is absorbed and metabolized, consequently influencing metabolite levels.
Interpreting High Carboxy-THC Levels
A high level of Carboxy-THC in a biological sample primarily indicates past exposure to cannabis. Since Carboxy-THC is a non-psychoactive metabolite, its presence does not signify current impairment or intoxication. The compound can remain detectable for weeks or even months after the last use, particularly in frequent users, due to its lipid solubility and slow release from fat cells.
Distinguishing between acute and chronic use based solely on Carboxy-THC levels can be challenging due to the long detection window and variability among individuals. While higher concentrations may suggest more frequent or heavier use, these levels do not precisely pinpoint the time of use or the degree of impairment. For example, studies show that Carboxy-THC levels in urine are not correlated with accident risk, unlike active THC in blood. Therefore, a positive Carboxy-THC test result confirms previous cannabis consumption, but it does not provide information about the recency of use or whether an individual was under the influence at the time of sample collection.