THC is the primary psychoactive compound in cannabis, responsible for its effects. Drug tests detect THC and its metabolites for employment, legal, and medical reasons. Many factors influence how long THC remains detectable.
Common Drug Test Methods
Several methods detect THC or its by-products. Urine tests are common, identifying a non-psychoactive metabolite called THC-COOH. They are favored for their ease and cost-effectiveness.
Blood tests detect active THC, indicating recent use. They are utilized in situations requiring a determination of recent impairment, such as accident investigations. Saliva tests collect an oral fluid sample, detecting the parent THC compound for very recent cannabis use. Hair follicle tests offer the longest detection window by analyzing drug metabolites incorporated into hair strands as they grow.
Understanding THC Cut-Off Levels
Drug testing uses “cut-off levels,” specific concentrations that must be met or exceeded for a sample to be considered positive. Measured in nanograms per milliliter (ng/mL), these levels distinguish actual use from incidental exposure. For urine tests, federal guidelines often set an initial screening cut-off at 50 ng/mL for THC metabolites.
If a sample screens positive, a confirmatory test, typically gas chromatography-mass spectrometry (GC-MS), is performed with a lower cut-off of 15 ng/mL to ensure accuracy. Saliva tests often have lower cut-off levels, with some detecting THC as low as 0.5 ng/mL or 12 ng/mL. Exceeding a predefined concentration indicates a positive result.
Factors Influencing THC Detection
Individual and usage factors impact how long THC metabolites remain detectable. Frequency and quantity of cannabis use are primary determinants; higher doses and more frequent consumption lead to greater accumulation. Chronic heavy use can saturate the body’s fat stores, extending detection times.
Individual metabolism plays a substantial role; those with faster metabolic rates process and eliminate THC more quickly. THC is fat-soluble, binding to fat molecules and storing in adipose tissue. Individuals with a higher body fat percentage typically retain THC longer as metabolites slowly release from these fat cells.
Hydration levels can also influence metabolite concentration, though excessive water intake primarily dilutes urine. Genetics and overall health, including liver function, further contribute to the variability in THC elimination rates.
Typical Detection Windows
THC detection windows vary by test method and individual factors. In urine, THC metabolites are detectable for about 3 days after a single use. Moderate users might show detection for 5–7 days, while chronic heavy users could test positive for 30 days or longer.
Blood tests generally detect THC for 2–12 hours after use, though it can be detectable for up to 7 days in chronic heavy users. Saliva tests can detect THC for up to 24-72 hours for occasional users, and potentially up to 7 days for regular users. Hair follicle tests offer the longest detection, identifying cannabis use for up to 90 days as metabolites embed in the hair shaft. Passive exposure to secondhand cannabis smoke is unlikely to result in a positive drug test, as absorbed metabolite concentration is generally below detection thresholds.