top of page

Search Blog Articles

  • Writer's pictureARCannabisClinic

Can Marijuana Be In Your System From Second Hand Smoke?

In an era where the legalization of marijuana is gaining traction worldwide, understanding the effects of secondhand marijuana smoke becomes crucial. Often compared with cigarette smoke, secondhand cannabis smoke can raise several questions, particularly concerning its potential to result in a positive drug test. Many factors can affect this possibility, including the potency of the cannabis, the ventilation of the space, and the duration of exposure. In this blog, we'll delve into the scientific research on this topic and shed light on the effects of secondhand smoke from marijuana.

Table of Contents:

Exploring the Dynamics of Secondhand Cannabis Smoke in an Enclosed Space

man smoking cannabis joint

While cannabis use is becoming more widely accepted and legal in numerous places around the globe, concerns regarding secondhand marijuana smoke, particularly in enclosed spaces, are growing. When a person smokes marijuana, the smoke released into the air contains various substances, including THC (Tetrahydrocannabinol), the principal psychoactive constituent of cannabis.

  • Unventilated Room vs. Well-ventilated Room: The degree of secondhand cannabis smoke exposure greatly depends on the ventilation of the room. In an unventilated room, the smoke concentration can remain high for an extended period, increasing the likelihood of THC absorption in non-smokers. On the contrary, a well-ventilated room can disperse smoke more rapidly, reducing the amount of THC in the environment.

  • Close Proximity and Number of Smokers: The proximity to the source of the smoke, and the number of marijuana smokers present, also play significant roles. Close proximity to cannabis smokers or a larger number of smokers in the room increases the passive exposure to secondhand weed smoke.

  • Duration of Exposure: Being in an enclosed space filled with marijuana smoke for a long period of time can increase the likelihood of inhaling detectable amounts of THC. A minute of exposure might not result in detectable levels of THC in bodily fluids, but an extended period could.

  • Effects of Secondhand Smoke: In extreme exposure situations (like a 'hot box' scenario), non-smokers may experience a contact high, with mild impairment and psychoactive effects due to the high THC concentrations in the air. This kind of scenario may also potentially lead to a positive urine test result for cannabis use.

  • Cigarette Smoke vs. Marijuana Smoke: It's important to note that marijuana smoke shares many harmful properties with tobacco smoke, such as hydrogen cyanide and other cancer-causing chemicals. So, exposure to secondhand cannabis smoke isn't benign.

  • Study Findings: A study by the Johns Hopkins University revealed that under extreme conditions, non-smokers exposed to secondhand marijuana smoke in an unventilated room had detectable amounts of THC in their urine and experienced mild psychoactive effects.

Key Takeaway: Secondhand cannabis smoke in an enclosed space can lead to detectable THC levels in a non-user under specific conditions such as poor room ventilation, close proximity to the smoker, and long exposure duration. While the likelihood of experiencing a 'contact high' or failing a drug test under normal environmental conditions is relatively low, it's crucial to be aware that secondhand marijuana smoke contains harmful substances similar to those found in cigarette smoke, underscoring the importance of adequate ventilation and minimized exposure.

Deciphering the Connection between Secondhand Marijuana Smoke and Drug Test Results

hands rolling cannabis joint

The correlation between secondhand marijuana smoke and drug tests has been a contentious topic for some time. Can exposure to secondhand cannabis smoke lead to a positive drug test result? Let's delve into this topic and explore the potential outcomes.

  • Detection of THC: Tetrahydrocannabinol (THC), the psychoactive component in marijuana, is what drug tests primarily look for. When someone smokes marijuana, THC enters their bloodstream and, after being processed by the body, is excreted through urine as THC metabolites. It's these metabolites that urine drug tests typically detect.

  • Influence of Environmental Factors: Several factors can impact the likelihood of a positive result due to secondhand marijuana smoke. The potency of the marijuana, the size of the enclosed space, the number of smokers, duration of exposure, and the room's ventilation can all influence THC concentrations in secondhand smoke.

  • Extreme Conditions Required: According to a study conducted by Johns Hopkins University, detectable levels of THC were found in the bodily fluids of non-smokers after they spent extended periods in extreme, unventilated exposure conditions - such as being in a small, poorly ventilated room with heavy marijuana smokers.

  • Standard Drug Test Thresholds: Typically, drug tests have a specific cutoff level for THC metabolites, often around 50 nanograms per milliliter. Most casual exposure scenarios don't lead to THC metabolite levels exceeding this cutoff, and hence, a positive test result is highly unlikely under normal circumstances.

  • Type of Drug Test: Different drug tests have varying detection periods and sensitivities. While urine tests can detect THC metabolites several days after usage, blood tests detect recent use more effectively, usually within hours. Saliva tests can detect THC within 24 hours of use, and hair follicle tests can detect THC even months after usage. The probability of a positive result from secondhand smoke exposure would greatly depend on the type of test used and its sensitivity.

Key Takeaway: While it is theoretically possible for a drug test to detect THC from secondhand marijuana smoke, the likelihood is quite low under most real-world conditions. It would require substantial, consistent exposure in a poorly ventilated environment for the THC levels to meet the cutoff for most drug tests. Nonetheless, understanding the dynamics of secondhand smoke and drug testing can help individuals make more informed decisions about their environment.

Evaluating the Potential Health Risks of Passive Exposure to Cannabis Smoke

Hand passing cannabis joint

One of the most frequently asked questions about secondhand marijuana smoke is whether it can result in a positive drug test result. Here's a closer look at the link between the two.

  • THC Levels from Secondhand Smoke: The core concern with secondhand marijuana smoke is the presence of THC, which is absorbed into the bloodstream and eventually excreted in urine. Urine tests for marijuana use typically look for the presence of THC metabolites, specifically THC-COOH. In a scenario with substantial exposure to secondhand cannabis smoke, small quantities of THC can indeed be absorbed by a non-smoker.

  • Extreme vs. Casual Exposure: Research from the National Institute on Drug Abuse and the Journal of Analytical Toxicology suggests that extreme, unventilated exposure to secondhand cannabis smoke can lead to detectable THC metabolites in urine. However, under normal, well-ventilated circumstances, the absorbed THC levels from secondhand smoke would likely fall below the drug test cut-off level, and a positive test result would be less likely.

  • Test Sensitivity and Cutoff Levels: Drug tests have different sensitivity levels, indicated by their cutoff levels. Most standard urine tests have a cutoff level of 50 ng/mL of THC-COOH. Only under severe, unventilated exposure to secondhand marijuana smoke might non-smokers reach this level.

  • Blood and Oral Fluid Testing: These tests detect recent marijuana use more effectively than urine tests. The detectable THC concentration in blood and oral fluids diminishes more quickly compared to urine. However, a study by John Hopkins University showed that extreme exposure to secondhand marijuana smoke could lead to a failed blood test.

  • Hair Testing: Hair tests can detect drug use over a more extended period (days to weeks). Although research is limited, it appears that extreme secondhand smoke exposure could potentially lead to a positive hair test, but this scenario is unlikely under everyday conditions.

Key Takeaway: The likelihood of failing a drug test due to secondhand marijuana smoke exposure is generally low under normal conditions. However, under extreme conditions, such as heavy marijuana use in an unventilated, enclosed space over an extended period, detectable levels of THC could potentially result in a positive drug test result. Therefore, it's crucial to understand the environmental factors that can influence exposure to secondhand cannabis smoke.

Practical Measures to Reduce Secondhand Marijuana Smoke Exposure

As awareness grows about the potential risks associated with secondhand marijuana smoke, it becomes essential to understand practical measures to minimize this exposure. Here are some strategies:

  • Ventilation is Key: Whether you're a smoker or a non-smoker, proper ventilation is crucial. If you're in a situation where marijuana is being smoked, try to be in a well-ventilated room or outdoors to allow the smoke to disperse more effectively.

  • Maintaining Distance: Keeping a safe distance from marijuana smokers can significantly reduce the amount of smoke you inhale. The closer you are to the source of the smoke, the higher your exposure.

  • Limiting Time in Smoky Environments: If you're in a room where people are smoking marijuana, limit the amount of time you spend there. The longer you're exposed, the greater the chance of inhaling secondhand smoke.

  • Air Purifiers: Consider using an air purifier to help clean the air of smoke particles. While they won't completely eliminate the risks, air purifiers can help reduce the concentration of smoke in indoor spaces.

  • No Smoking Policies: Implementing a no smoking policy in shared spaces, like homes and cars, can drastically reduce exposure to secondhand marijuana smoke.

  • Educate Yourself and Others: Understand the potential risks of secondhand marijuana smoke and share this knowledge with others. Awareness is a significant step in reducing exposure.

  • Using Smokeless Methods: If you're a medical marijuana user, consider smokeless methods of consumption like edibles, tinctures, or vaporizers. These methods can significantly reduce smoke exposure for those around you.

Key Takeaway: Secondhand marijuana smoke exposure can be significantly reduced through various practical measures. Proper ventilation, maintaining distance from the source of smoke, limiting time spent in smoky environments, and using smokeless methods of consumption can all contribute to minimizing exposure. It's important for both smokers and non-smokers to be mindful of the potential risks of secondhand smoke and to take steps to reduce these risks in shared environments.


Q: Can secondhand marijuana smoke result in a positive urine test?

A: Under extreme conditions, such as in an unventilated room with heavy marijuana use over an extended period, a non-user might experience a "contact high" and might have detectable amounts of THC in urine samples.

Q: What are the health risks associated with secondhand marijuana smoke?

A: Studies suggest that secondhand cannabis smoke has many of the same cancer-causing chemicals as tobacco smoke, and may also affect blood vessels, much like secondhand tobacco smoke.

Q: Can you get high from secondhand marijuana smoke?

A: Under regular environmental conditions, getting high from secondhand marijuana smoke ("contact high") is unlikely. However, in an extreme exposure scenario, such as in a hot box situation (a small, poorly ventilated room), it might be possible to experience mild psychoactive effects.

Q: Are there long-term effects of exposure to secondhand marijuana smoke?

A: As of now, the long-term effects of secondhand cannabis smoke are not well understood. However, ongoing research aims to reveal the potential long-term health risks.


Secondhand marijuana smoke is a complex issue. While extreme exposure in small, unventilated rooms might lead to detectable THC levels and mild impairment, the likelihood of a failed drug test or experiencing a "contact high" under normal environmental factors is relatively low. However, the presence of cancer-causing chemicals in marijuana smoke warrants concern and underlines the importance of limiting exposure, particularly in enclosed spaces.

If you are considering marijuana use, particularly for medical purposes, it's important to be well-informed about its potential effects, including those related to secondhand smoke. At ARCannabisClinic, we offer personalized expert MMJ treatment plans and dosing to ensure safe and effective use of medical marijuana. Our providers also offer MMJ Therapy Visit. We can guide you through the process, helping you make the best decisions for your health and wellness.

Recent Posts

See All


doctor talking to a patient about medical marijuana as an option for treatment


Experience the convenience of ARCannabisClinic's online doctor visits, offering professional, compassionate, and comprehensive marijuana-based medical advice, all at your fingertips.

medical marijuana patient happy and smiling talking to a marijuana doctor
bottom of page