Frequently Asked Questions


Dr. Mike Lynn founded Hound Labs, because he passionately believes the tragedies associated with impaired driving are preventable. As an ER physician at a trauma center and a reserve deputy sheriff, Dr. Lynn has witnessed the consequences of impaired driving too often.

The Hound® marijuana breathalyzer is easy to use, like an alcohol breathalyzer. A driver or employee breathes into the mouthpiece on the breathalyzer. The disposable cartridge on the breathalyzer automatically captures two breath samples. After the breath samples have been collected, the cartridge is removed and placed in a small portable processor that then measures alcohol and THC in one of the samples. Within a few minutes, the results for both alcohol and THC are displayed. If desired, the cartridge can be saved so the second sample can be analyzed in the future.

Yes, the Hound® breathalyzer measures THC in breath to levels as low as 1 trillionth of a gram, or 1 picogram per liter of breath (1pg/L). This is the sensitivity required to measure recent marijuana use throughout the 2-3 hour window of peak impairment identified by researchers.

Yes. Our breathalyzer is able measure THC in the breath after subjects have consumed a variety of smoked, vaporized, and edible marijuana products.


Breath is a better indicator of impairment than blood, urine, or saliva because THC only remains in breath for a few hours before becoming virtually undetectable, whereas it can remain in other body fluids for many hours, days, or even weeks after smoking. The period of time during which THC can be measured in breath aligns with the peak impairment window (2-3 hours) identified by independent researchers [NHTSA]. This makes a marijuana breathalyzer the best objective test for determining whether a person used marijuana recently and could still be impaired, which is in what employers and law enforcement are interested.


Yes. Although well-intended, some states have set blood limits for THC to indicate whether a driver is impaired and dangerous behind the wheel. Unfortunately, high levels of THC can remain detectable in blood for days or even weeks, well beyond any impairment window (2-3 hours) identified long ago by independent researchers [NHTSA]. This “positive” result means that many people who are not impaired will fail oral fluid, blood, and urine tests. Some of these are legacy laws, created at a time when use of marijuana generally was illegal and “zero tolerance” laws could be enforced regardless of whether or not the presence of THC was causing impairment behind the wheel. And all of these per se laws were established before the Hound® marijuana breathalyzer was available.

With the legalization of marijuana, legislators are beginning to realize that they need new laws to accommodate legal and responsible marijuana use while still deterring and monitoring impaired driving and working. A marijuana breathalyzer is the best way to balance safety and fairness in the era of marijuana legalization because a marijuana breathalyzer only measures THC in breath for the few hours that correlate with peak impairment – NOT the presence of THC long after impairment subsides. Understanding whether someone recently used marijuana is a key piece of data to help law enforcement and employers determine whether or not the driver or employee may be impaired.  

Until commercialization of the Hound® breathalyzer, no marijuana breathalyzer was available, and no municipal or state governments were able to establish legal limits for THC in breath. Per se laws are typically based on blood levels, but the problem is that THC can remain in blood in high concentrations long after peak impairment subsides. This makes these laws unfair to those drivers who smoked marijuana days or weeks before driving and still have THC in their blood but are no longer impaired. The important data is whether marijuana was used recently enough to be within the window of peak impairment. The presence of THC in the breath indicates recent use because it only stays in breath 2-3 hours after smoking.

Employers, law enforcement, legislators, unions, and others have communicated an immediate need for the Hound® marijuana breathalyzer to help them objectively determine recent marijuana use. The only tools available right now measure THC in blood, urine, and saliva, where it can remain long after impairment subsides. These tests were useful when marijuana use was illegal and the only data that law enforcement and employers needed was to indicate the mere presence of THC in body fluids.

The Hound marijuana breathalyzer measures THC in breath which indicates that someone has smoked marijuana in the last few hours – the same time frame as the peak window of impairment. Thus, even without laws specifically related to breath levels of THC, a measurement from the Hound breathalyzer provides critical data about recent use which can help inform officers’ and employers’ decisions.

For historical context, alcohol breathalyzers were used well before per se limits were standardized. They provided useful information to law enforcement regarding recent alcohol use.


We have had a great deal of interest in our breathalyzer from law enforcement and employers in the U.S. and across the globe and continue to receive new inquiries regularly. We are currently finalizing charter customer agreements with law enforcement agencies and employers.

We have tested versions of the Hound® marijuana breathalyzer with law enforcement as part of the development of the tool. Multiple law enforcement agencies are planning to use our breathalyzer when it becomes available.

We cannot comment on our relationships with individual police departments or employers at this time.


The trial found that THC is reliably detectable in breath for three hours after smoking marijuana. By around the three-hour mark, THC levels drop to virtually undetectable levels. The three-hour timeframe is significant because research* has shown that this is the prime window during which people are most likely to be impaired after smoking marijuana. Other marijuana tests – urine, blood, oral fluid, hair – detect past use, well outside the window of peak impairment. With the legalization of marijuana, tests that detect past use become largely irrelevant to employers and law enforcement. The question is no longer whether someone has used marijuana at some point in the past, but whether they are high at a given point in time.

*April 2014 National Highway Traffic Safety Administration’s “Drugs and Human Performance Fact Sheet”

These results are significant for a number of reasons. They:

  1. Validate that THC is detectable in breath using Hound technology during the peak window of impairment.
  2. Demonstrate the need for ultra-sensitive technology in order to measure THC throughout the three-hour window of peak impairment after smoking.
  3. Confirm that breath is a better way to determine recency of use. Testing other mediums – oral fluid, blood, urine, hair – has not shown this ability to isolate recent use.
  4. Demonstrate that the Hound technology enables researchers to conduct cutting edge research to expand the frontiers of our collective scientific understanding of the effects of THC use.

Methods: In alignment with best practices for this type of research, the UCSF study included 20 participants, men and women who were frequent and infrequent smokers. Participants smoked marijuana they brought themselves. They smoked in a highly ventilated room designed specifically for smoking studies – completely separated from the research rooms in order to avoid any possible contamination. The research team collected breath and blood samples at nine specified intervals throughout a three-hour window after smoking. All participants provided consent prior to joining the study.

An Institutional Review Board (IRB) approved this research. The IRB reviews research conducted by UCSF clinical staff in order to protect subject rights and oversee subject welfare.


Hound Labs does not take a stance on marijuana legalization. We do, however, take a stance on driving or working under the influence of marijuana: Don’t do it.