A “contact high” refers to the effects experienced by an individual who passively inhales secondhand cannabis smoke. A common concern among those exposed to secondhand smoke is whether this passive exposure can lead to a positive result on a drug test. This article explores the scientific evidence surrounding this question, aiming to provide clarity on the likelihood of such an outcome.
How Cannabis Drug Tests Work
Drug tests for cannabis primarily detect delta-9-tetrahydrocannabinol (THC), the main psychoactive compound, and its metabolites. When cannabis is consumed, THC is absorbed into the bloodstream and processed by the liver into byproducts, most notably 11-nor-9-carboxy-delta-9-tetrahydrocannabinol, known as THC-COOH. This non-psychoactive metabolite, THC-COOH, is what most drug tests identify, as it remains detectable longer than THC itself.
Urine tests are the most frequently used method for detecting cannabis use, looking for THC-COOH. These tests have a specific detection threshold, often 50 nanograms per milliliter (ng/mL), though this can vary. If the THC-COOH concentration in the urine sample is above this cutoff, the test is positive. Other testing methods include blood tests, which detect active THC and have a shorter detection window, and saliva and hair tests, which also look for THC or its metabolites.
Passive Inhalation and Drug Test Detection
While trace amounts of THC can be inhaled passively, it is difficult to ingest enough to exceed common drug test detection thresholds under typical social circumstances. Research shows that THC levels in non-smokers after secondhand exposure are usually below the cutoff levels for a positive test. For instance, the amount of THC absorbed through secondhand smoke is often about 100 times less potent than from active exposure.
Positive results from passive exposure are rare and require extreme, unventilated conditions. One study with participants in a confined, unventilated space with heavy marijuana smoke found that while some had detectable THC in their urine, most results were below the 50 ng/mL cutoff. Only in such severe conditions did some individuals briefly test above this limit. A study on oral fluid testing concluded that the risk of a positive test from passive smoke inhalation is limited to approximately 30 minutes following exposure.
Factors Influencing Detection Risk
Several factors can increase the risk of detectable passive inhalation, though it remains generally unlikely. The amount of cannabis smoked and the level of ventilation are key. Higher THC concentrations in the air increase potential inhalation, and a small, unventilated room presents a higher risk than open-air exposure.
Proximity to the smoker and duration of exposure also contribute. Sitting directly next to an active smoker in a confined space for an extended period increases THC absorption. Conversely, exposure in well-ventilated areas, like outdoors, significantly reduces THC concentration, making absorption for detection very unlikely. The sensitivity of the drug test used also matters, as some tests have lower cutoff levels that could potentially detect trace amounts standard tests might miss.
Addressing Concerns and Prevention
Individuals concerned about passive exposure can take steps to minimize potential risk. Ensuring good ventilation in shared spaces is effective; if cannabis is smoked, being in a well-ventilated area or outdoors significantly reduces exposure. Maintaining distance from smokers also helps, especially in enclosed environments like cars or small rooms.
Avoiding prolonged exposure in enclosed spaces where cannabis is actively smoked is another preventive measure. While it is highly unlikely for typical passive exposure to lead to a positive drug test, these actions can further reduce any minimal risk. Commonly used drug tests are designed with cutoff levels to differentiate between active use and incidental secondhand exposure.