A “contact high” refers to feeling cannabis effects without direct consumption, typically through passive inhalation of marijuana smoke. This often raises questions about whether such exposure can lead to a positive drug test. While absorbing enough tetrahydrocannabinol (THC) from secondhand smoke to feel intoxicated or fail a test might seem plausible, scientific evidence suggests this is unlikely under most common circumstances.
Understanding Drug Tests
Cannabis drug tests primarily look for specific metabolites the body produces after processing THC, rather than the active compound itself. The main metabolite targeted is 11-nor-9-carboxy-THC, commonly known as THC-COOH. This metabolite is stored in fat cells and can remain in the body for an extended period after THC consumption.
Various methods are used for cannabis drug testing, each with different detection windows. Urine tests, the most common, detect THC-COOH for 1 to 30 days, or longer for chronic heavy users. Saliva tests typically have a shorter detection window, usually up to 24-72 hours. Blood tests can detect THC for a few hours to several days. Hair follicle tests are the most sensitive, detecting cannabis use for up to 90 days or more, as THC metabolites become embedded in the hair shaft.
Scientific Findings on Passive Exposure
Scientific studies have investigated whether passive exposure to cannabis smoke can result in detectable levels of THC or its metabolites. Under typical conditions, such as brief exposure in a well-ventilated area, passive inhalation is highly unlikely to lead to a positive drug test result. The amount of THC absorbed by a non-smoker in these scenarios is usually minimal, quickly metabolized, and stays well below standard detection thresholds.
However, in extreme situations, such as prolonged exposure in a small, unventilated space with a very high concentration of smoke, detectable levels of THC metabolites could occur. Even in these rare instances, the levels detected are often still below the established cutoff thresholds used by most drug tests for a positive result. For instance, the common cutoff for initial urine drug screens for THC-COOH is 50 nanograms per milliliter (ng/mL), with confirmatory tests often set at 15 ng/mL. These thresholds are specifically designed to minimize false positives from passive exposure.
Factors Affecting THC Detection
Several variables influence the likelihood of THC metabolites being detected after passive exposure. The most significant factors include the amount of smoke present and the level of ventilation. Poorly ventilated, enclosed areas (e.g., a small room or a car) significantly increase secondhand smoke concentration and absorption potential.
The duration of exposure also plays a role; longer periods in a smoke-filled environment increase the chances of inhaling detectable amounts. Higher cannabis potency contributes to greater airborne THC concentrations. Individual metabolic differences, body composition, and hydration levels also affect how quickly any absorbed THC metabolites are processed and eliminated.
Reducing Risk and What to Consider
For individuals concerned about potential passive exposure, several practical steps can minimize risk. Avoiding environments with heavy cannabis smoke is the most direct approach. If presence in such a space is unavoidable, ensuring good ventilation (e.g., opening windows or doors) can significantly reduce airborne smoke concentration. Maintaining distance from the smoke source also helps limit inhalation.
If anticipating a drug test after potential passive exposure, honesty with the testing facility or employer about the circumstances can be beneficial. While extreme circumstances rarely lead to detectable levels, avoiding heavy secondhand smoke is sensible. Staying adequately hydrated supports normal bodily functions, though excessive water intake can dilute samples, potentially leading to an invalid test result.