Human Metabolism of THC: What Happens in Your Body When You Consume Cannabis
When someone lights up a joint or eats a cannabis-infused edible, they’re not just getting high. They’re initiating a complex biochemical journey within the body that has important implications for detecting impairment and therefore, safety. This journey, which transforms the plant's key psychoactive molecule, Delta-9 Tetrahydrocannabinol (THC), into various metabolites, is an intricate interplay of enzymes, liver cells, and receptors. It’s a story of how psychoactive chemicals travel through the human body, affecting both the mind and various other systems.
The Chemistry of the High
At the heart of cannabis's allure lies Delta-9-Tetrahydrocannabinol (referred to as just “THC”), the primary psychoactive molecule responsible for the euphoria, altered perception, and other aspects of the high. But THC doesn’t act alone. Once it enters your system, it becomes part of a molecular dance, with different enzymes and pathways coming into play depending on how you consume the cannabis.
When you inhale cannabis smoke or vapor, THC is absorbed through the lungs, where it swiftly crosses into your bloodstream. Within minutes, it's circulating through the body, making its way to the brain, where it binds to cannabinoid receptors—specifically, the CB1 receptors. These receptors are like tiny locks, and THC is the key that fits just right, triggering the psychoactive effects we associate with cannabis.
However, the story takes a different turn when someone eats cannabis. Instead of a rapid rise in THC levels as a result of the very efficient lung to bloodstream mechanism, the process with edibles is much slower. The THC must first pass through your digestive system, where it's absorbed through the walls of your stomach and intestines. From there, it enters the liver, and this is where the magic—and the science—really begins.
The Liver's Role: Transformation and Potentiation
The liver is like a biochemical factory, bustling with enzymes ready to break down substances into more manageable pieces. When THC arrives, the liver enzymes, primarily the cytochrome P450 family, get to work. They convert Delta-9-THC into 11-Hydroxy-THC (11-OH-THC), a metabolite that’s even more potent than its parent compound.
This transformation is a crucial part of why edibles hit differently than smoked or vaped cannabis. 11-OH-THC can cross the blood-brain barrier more easily than Delta-9-THC, leading to a more intense and often a significantly longer-lasting high. This explains why the effects of an edible can take longer to kick in but linger much longer than when you smoke or vape cannabis.
THC's Slow Fade from the Body
Once THC has done its job—whether it’s helped someone relax, stimulated their creativity, or just made their pizza taste better—it doesn’t immediately vanish. Instead, your body continues to break it down, eventually turning it into THC-COOH (11-COOH-THC), a non-psychoactive metabolite. This is the form of THC that lingers in your system, stored in fat cells and slowly released over time.
This slow release is why THC is detectable in your body for days, weeks, or even longer, depending on how frequently you use cannabis. This presents a massive problem for businesses and law enforcement that use metabolite based drug testing to keep roads or workplaces safe. Since the metabolites of THC stick around for so long, measuring those metabolites is of zero predictive value for current impairment. We’ll soon explore why the same is broadly true for the parent molecule (Delta-9-THC).
Inhaling vs. Ingesting: A Tale of Two Highs
The route one chooses for consuming cannabis—whether smoking, vaping, or eating—significantly impacts how THC is metabolized and, consequently, the kind of high one experiences.
Inhaling delivers a quick, intense high that peaks within minutes and fades within 90 minutes to two hours. This is due to the rapid absorption of THC into the bloodstream and its swift binding to CB1 receptors in the brain. The bioavailability of inhaled THC (how much of it actually makes it into your system) is relatively low, ranging from 10% to 35%, due to factors like combustion and loss of THC in exhaled smoke.
On the other hand, ingesting cannabis is like taking the scenic route. The high is slower to start—often taking 30 minutes to 2 hours to fully kick in—but when it does, it’s often more intense and lasts much longer, sometimes 4 to 8 hours or more. This is because of that powerful 11-OH-THC metabolite, which the liver produces in abundance when THC is processed through digestion.
Bioavailability: How Much THC Are You Actually Getting?
Bioavailability is a fancy term for the amount of a substance that actually makes it into your bloodstream and becomes available to have an active effect. When it comes to THC, bioavailability varies greatly depending on how you consume it.
Smoking/Vaping: The bioavailability of smoked or vaporized THC hovers around 10-35%. This means that out of all the THC in the cannabis you consume, only a small fraction ends up in your bloodstream. The rest is lost to combustion, heat, or simply never absorbed and ultimately exhaled.
Edibles: THC in edibles has a lower initial bioavailability of about 4-20% due to the digestive process and the first-pass metabolism in the liver. However, the conversion to 11-OH-THC compensates for this, as this metabolite is more potent and longer-lasting.
Sublingual/Topical: These methods bypass the digestive system and liver, leading to higher bioavailability compared to edibles but still lower than inhalation.
The Half-Life of THC: How Long Does It Stick Around?
The half-life of a drug is the time it takes for its concentration in the blood to decrease by half. For THC, the half-life varies widely depending on the method of consumption, frequency of use, and individual metabolism.
Inhaled THC: The half-life is relatively short, ranging from 1 to 4 hours. This rapid clearance is why the effects of smoking or vaping typically fade within a few hours.
Ingested THC: The half-life of 11-OH-THC can be much longer, up to 12-26 hours or more. This extended half-life contributes to the prolonged effects of edibles and their ability to linger in the body for days after consumption.
The Metabolism of THC is a Personalized Experience
THC metabolism is as unique as the person experiencing it. Factors like their genetic makeup, the method of consumption, potency of the product consumed, tolerance and even what they’ve eaten that day can all influence how THC is metabolized and how long its effects last. Understanding these processes is challenging, and even experienced cannabis users can be surprised by the strength of an edible from time to time, which introduces significant safety risks.
As cannabis becomes more socially accepted and legalized across the globe, society is navigating new challenges—one of the most pressing being how to accurately assess impairment. Unlike alcohol, where a simple breathalyzer can quickly determine current impairment, THC and its effects are far more subtle and complicated to measure. This complexity has significant implications for drug testing and has spurred the development of cutting-edge impairment detection technology.
The Problem with Traditional Drug Tests: Prior Use vs. Impairment
If you’ve ever had to take or administer a drug test for work, you know the drill: pee in a cup or do a mouth swab, send it off to the lab, and wait for the results. In some cases, preliminary results may be available in 15-30 minutes, but lab confirmations still take a week or more. But what exactly are these tests looking for? When it comes to THC, the most common drug tests—whether urine, or hair—aren’t looking for the active compound that gets you high. Instead, they’re searching for its metabolites, primarily THC-COOH (11-COOH-THC), the non-psychoactive byproduct of THC metabolism.
Unfortunately for safe and responsible cannabis users, THC-COOH can linger in your system long after the effects of THC have worn off. For occasional users, it might hang around for a week or two. But for regular or heavy users, these metabolites can be detected for over a month after the last use.
Some drug testing companies have tried to conflate the detection of the parent compound, Delta-9-THC, with recent use or impairment. That’s simply not true. There is no scientific evidence to support any amount of THC in the blood, breath, or saliva being associated with current impairment. What is true is that Delta-9-THC is detectable for a much shorter period of time than metabolites. Saliva tests, as an example, and typically positive for up to 48 hours since the last use of marijuana. While this is more recent, it’s certainly not within the window of acute impairment. This means someone could test positive for cannabis use long after the high has faded—potentially putting their job or legal standing at risk, even if they’re not impaired at the time of the test.
The Flawed Logic of Chemical Testing
The persistence of THC and its metabolites in the body poses a significant problem. Traditional drug tests don’t measure impairment; they measure prior exposure to the drug. This distinction is crucial. A positive test result simply indicates that a person has used cannabis at some point in the recent past. It doesn’t tell you if they’re currently under the influence or if their ability to perform tasks—like driving, operating machinery, or making decisions—is impaired.
This approach contrasts sharply with alcohol testing. When you blow into a breathalyzer, it measures the amount of alcohol currently in your system. Because of the way that alcohol is metabolized and used by the body, the amount of alcohol in the body mirrors the experienced impaiment. This is why the breathalyzer or a blood-alcohol test is useful for an immediate snapshot of your level of intoxication. With THC, since it’s metabolism is so different, simply measuring it in the body is not useful for determining real-time impairment.
Applying chemical tests to police legal cannabis users is therefore illogical and deeply unfair. This is the reason that the category of impairment detection technology was created.
The Rise of Impairment Detection Technology
Enter impairment detection technology—a game-changer in the quest to fairly and accurately assess whether someone is fit to perform specific tasks, even with chemical biomarkers of drugs in their body. Unlike traditional drug tests that look for THC and its metabolites, impairment detection technology focuses on measuring how the body is responding, thereby measuring current levels of impairment. These technologies are designed to evaluate how drugs like THC affect the brain and body using specially designed tests.
Several companies are developing or have launched tools to fill this gap. These tools measure cognitive and motor function. They don’t measure THC levels at all, but instead measure how you’re performing using non-invasive techniques. Are your reaction times slowed? Is your attention wavering? These are the indicators of impairment that matter in the real world—whether you’re behind the wheel, on the job, or making important decisions.
There are several types of impairment detection technology. We strongly believe the best and most accurate is our’s - Gaize. Please look around at the others though and make the decision that feels right for your company and situation.
Why This Matters: Fairness, Safety, and the Future of Cannabis Use
As cannabis continues to be legalized and de-stigmatized, the need for fair and accurate impairment testing becomes increasingly important. The stakes are high. In workplaces, employers need to ensure safety without unjustly penalizing employees who use cannabis responsibly. On the roads, law enforcement must distinguish between those who are impaired and those who safety enjoy the occasional joint or edible.
Impairment detection technology offers a solution that respects both safety and offers fairness for cannabis users. It acknowledges the reality that cannabis is different from alcohol, requiring a more nuanced approach to assessing impairment. This technology is in use today, revolutionizing how we handle cannabis use in society, moving us away from outdated and often unfair chemical drug testing methods.
The Road Ahead: Embracing the New Era of Cannabis Testing
The conversation around cannabis and impairment is evolving rapidly. As we embrace this new era of impairment detection over legacy and invasive chemical tests, it’s essential to improve education around the metabolic dynamics of cannabis in the body. Doing so not only protects public safety but also ensures that individuals who use cannabis responsibly aren’t unfairly penalized.
Impairment detection technology represents the future of cannabis testing—a future where we move beyond the blunt tool of chemical detection to a more precise, fair, and scientifically sound method of evaluating impairment. In this way, we can finally align our policies and practices with the realities of how THC works in the body, ensuring that we’re making decisions based on what really matters: whether someone is truly impaired right now, not whether they were high last weekend.
