Interest in understanding how THC is transformed within the body continues to grow, both in the healthcare, legal, and labor sectors. In particular, attention is focused on the metabolic pathway that converts THC into compounds such as 11-hydroxy-THC and THC-COOH, key to interpreting detection tests and to understanding why their effects and traces last so long in the body.
In the following lines we break down in detail what THC is, how it acts and how it is metabolized, what role it plays THC-COOH as a biomarker of consumptionWhat are the detection windows in saliva, urine, blood, and hair, what factors accelerate or slow down its clearance, and what does the evidence say about dependence, withdrawal, risks, treatments, and even toxicity in animal models?
THC: what it is, how it works, and why it matters
Tetrahydrocannabinol, also called THC, Δ9-THC, dronabinol or dronabinolumIt is the main psychoactive component of cannabis. It was first isolated in 1964 thanks to the work of Gaoni and Mechoulam and, in its pure state, is a glassy solid at low temperatures that becomes viscous with heat, slightly soluble in water but very soluble in... organic solvents and lipids.
Its effects are due to the partial activation of cannabinoid receptors CB1 (brain and nervous system) and CB2 (immune system). By activating CB1, it decreases adenylate cyclase and cAMP, modulating neurotransmitter release. Hence, it affects movement, sensation, memory, perception of time, reward, and judgment.
Among the acute effects described are altered senses, changes in time perception, deterioration of coordinationMemory and attention problems, mood swings, anxiety, fear, paranoia, and, in some cases, hallucinations. It can also increase appetite and produce relaxation or euphoria, in addition to exerting moderate antiemetic and analgesic properties.
THC is strongly lipophilic, binds non-specifically to fatty tissues, and exhibits very high plasma protein binding (95-99%In humans, its bioavailability is around 10–35% by inhalation and 6–20% orally; its plasma half-life varies from 1,6 to 59 hours (approx. 25–36 hours orally), with predominant elimination via feces (65–80%) and urine (20–35%) as acid metabolites.
Other properties have been described: possible anticholinesterase activity in preclinical studies, moderate neuroprotective antioxidant activity against oxidative stress, and high absorption of UV-B radiation which could protect the plant. Tolerance phenomena are also observed, with downregulation of CB1 and variability between brain regions and types of effect.
THC-COOH: the metabolite that betrays consumption
11-nor-9-carboxy-THC, abbreviated THC-COOHTHC-COOH is the inactive metabolite of THC that drug tests most frequently look for. Unlike psychoactive THC, THC-COOH does not activate CB1/CB2 receptors, but its prolonged presence makes it a robust exposure marker after consuming cannabis.
THC-COOH is generated in the liver after a two-step biotransformation: first, THC is oxidized to 11-hydroxy-THC (11-OH-THC)which is psychoactive, and then forms THC-COOH, which is inactive. Due to its persistence, it is the key parameter in urine screenings, medical evaluations, workplace and legal settings. monitoring of therapeutic adherence and toxicology.
Historically, the study of THC metabolites and their detection has been driven by pioneers in forensic toxicology, laying the foundations for the analytical methods in blood and urine which are now considered standard in clinical and forensic laboratories.
From the lungs or stomach to the liver: this is how THC is metabolized
After smoking or vaporizing, THC passes from the lungs into the blood and quickly reaches the brain and organs; orallyIt is absorbed through the gastrointestinal tract and undergoes significant first-pass hepatic metabolism. In both cases, the liver metabolizes THC primarily through enzymes of the cytochrome P450 (e.g., CYP2C family).
The main pathway first generates 11-OH-THC and then THC-COOHThis biotransformation explains why edibles, despite taking longer to take effect (30–120 minutes), can produce more intense and lasting sensations: 11-OH-THC is psychoactive and can contribute to prolonged effects.
Due to its lipophilicity, THC is distributed to fat-rich tissues and accumulates in chronic users faster than it is eliminated. Over time, it is released back into the bloodstream and returns to the liver to be metabolized, so that in regular consumers Detection can take many days after the last use.
Key pharmacokinetic parameters reported include: bioavailability of 10–35% (inhalation) and 6–20% (oral), protein binding of 95–99%, long half-life (1,6–59 h) depending on the route and context, and total combined excretion mainly through feces, with a significant urinary fraction of acidic metabolites.
Detection windows: saliva, urine, blood and hair
The presence of cannabis and its metabolites depends on the type of sample, the sensitivity of the technique, the frequency and amount of consumption, and individual characteristics (metabolism, BMI, hydration). These are indicative ranges cited by laboratories and reviews:
- Spittle: It is usually detectable between 34 and 48 hours; some panels mention up to 72 hours in certain scenarios and with high sensitivity.
- Blood: THC and/or its metabolites can be detected up to approx. 36 hours in occasional users, with greater persistence in frequent consumers.
- Urine: This is the most common test. Sporadic use (less than 2 times/week): 1–3 days; intermediate use (several times/week): 7–21 days; heavy use: one month or more. Oral intake It can test positive 1–5 days.
- Hair: In hair follicles, detection can last up to 90 days; it is usually more reliable for daily or almost daily uses for very light consumption.
Beyond the method, factors such as the potency of the product (THC content), the amount consumed, the time since last use, and the metabolic rate The individual's hydration level and body fat percentage are factors. In chronic users, the slow release of fat deposits allows for prolonged detection.
Important in the workplace and legal context: in Spain there is no general rule that mandates drug testing at work, but the health surveillance related to job risks It may require consent-based assessments when the activity involves danger. On the road, alcohol and drug tests are mandatory, and a positive result can occur even if consumption occurred days earlier. especially in saliva or urine.
Attempts to manipulate evidence and why they don't work
Urine “detox” kits containing ingredients such as goldenseal, vinegar, niacin, vitamin C, or herbal teas are circulating. Evidence indicates that They do not accelerate metabolism or elimination of THC-COOH significantly, and may be useless or dangerous.
Other attempts include masking the urine with salt, bleach, or chemicals, or replacing it with foreign or synthetic samples. Laboratories apply integrity tests These tests detect masking agents and verify temperature, density, pH, color, odor, dilution, and the presence of endogenous compounds (such as creatinine). These techniques make the tricks unreliable, with the risk of penalties.
Clinical cases have been published that describe adverse effects after using kits of “detox”; for example, a psychotic episode temporally linked to a homemade product whose ingredients could compromise the liver. Even compounds like creatine have been associated with acute psychiatric reactions in isolated reports; beyond these examples, the message is clear: cheating is not a safe or guaranteed way out.
THC vs. THC-COOH: key differences
THC is the psychoactive agent, while THC-COOH is inactiveThe first causes the perceptual and behavioral effects; the second serves as a trace of previous use. In drug tests, the stable and lasting signal is usually the THC-COOH in urinenot the THC itself.
THC is metabolized quickly and explains the immediate effects; THC-COOH, being more persistent and accumulating in fat, is eliminated slowly. allowing detection weeks later in regular users. At a therapeutic level, THC has approved uses (e.g., antiemetic, analgesic in specific contexts), while THC-COOH lacks of medical applications.
Consumption methods and start times
Smoking or vaping produces almost instant effects that last 1 to 3 hours. Edibles take 30 minutes to 2 hours to take effect and can last 4–6 hours or more. topics They offer local relief without reaching the bloodstream, so they do not produce systemic psychoactive effects.
When smoked, THC quickly reaches CB1 receptors, altering perception, mood, coordination, memory, and signs of appetiteWhen taken orally, the first-pass hepatic metabolism increases the proportion of 11-OH-THC, which can intensify and prolong the effects depending on the dose and the individual.
Effects and risks: what the evidence shows
In the short term, use can cause altered senses, temporal distortionPoor coordination, difficulty thinking or solving problems, memory lapses, mood swings, anxiety, paranoia, hallucinations, and increased appetite. The duration depends on the method of consumption and the potency.
In the long term, daily and high-potency consumption has been associated with a greater likelihood of mental health problems. Some meta-analyses and studies They point to an increased risk of psychotic disorders, with a particularly notable impact on heavy users and products with higher THC content. Other side effects have also been described. epigenetic changes in research that suggests potential transgenerational transmission in experimental models.
In the gastro-hypothalamic axis, CB1 activation is related to increased appetite and the modulation of signals such as ghrelin, leptin, and cholecystokinin; likewise, animal models They indicate that THC enhances the hedonic response to sweet solutions via dopamine in the nucleus accumbens.
Dependence, withdrawal, and treatment
Contrary to the myth, marijuana can generate dependenceClinicians diagnose cannabis use disorder according to established criteria; it is estimated that around 30% of users will develop some degree of disorder, and those who start before the age of 18 present a risk 4–7 times greater.
Upon cessation of use, withdrawal typically appears within 24–72 hours, peaks during the first week, and resolves within 1–2 weeks. Symptoms include Headache, irritability, depression, anxiety, insomniaabdominal pain, decreased appetite, fever/chills, sweating, and tremors.
There are no drugs specifically approved for this withdrawal, but supervised detoxification It offers symptomatic support. Studies have explored options such as zolpidem for sleep, buspirone for anxiety, and gabapentin for neurological symptoms, with promising results in certain profiles.
The interventions with the strongest evidence combine psychosocial approaches: cognitive-behavioral therapyMotivational interviewing and contingency management are especially useful when other mental health disorders coexist.
Individual factors that modulate elimination
Metabolism varies between people because genetic factorsage and general health, affecting the clearance rateA high BMI tends to be associated with greater deposition of metabolites in adipose tissue and slower release.
Staying well-hydrated and exercising can modestly help with excretion through urine and sweat, although there is no evidence that these measures drastically accelerate the elimination of [the virus/carbohydrate]. THC-COOH in chronic users. The method of consumption also matters: what is inhaled is eliminated more quickly than what is ingested.
Illustrative case studies
Below are five profiles that show the interindividual variability in detection:
Occasional user (monthly consumption, inhaled): undetectable levels in blood and urine around day 5; in saliva, positive for about 24 hours after the last inhalation.
Regular user (4–5 times/week, edibles and flowers): positive urine for up to 30 days; blood for up to 7 days; saliva up to 72 hours.
Chronic user (daily, multiple doses): Detectable metabolites in urine for up to 90 days after last use; in blood for up to 30 days; saliva for approximately 7 days; in hair, traces for more than 6 months depending on growth.
User with high BMI (weekly, inhaled): positive urine for up to 45 days; blood for about 10 days; saliva for about 48 hours, reflecting the effect of adipose tissue on retention.
Elderly user (monthly, dye): Urine detectable for about 10 days; blood for 3 days; saliva for about 24 hours, with possible influence of age-related metabolic slowdown.
Toxicity, safety and antagonists
They have not been documented human fatalities by overdose of cannabis in its natural form. THC toxicity has been characterized primarily in animals and depends on the route of administration and the species: in rats, reported oral LD50s range from ~666 to 1270 mg/kg in males and 730 mg/kg in females; by inhalation, ~42 mg/kg; by intravenous, ~29 mg/kg. In mice, the ranges include ~482 mg/kg (oral) and ~42 mg/kg (IV); in dogs, ~525 mg/kg (oral); and minimum lethal dose data have been reported in monkeys via IV (~128 mg/kg).
High liposolubility and "buffering" by fat compartments have been proposed as factors that mitigate acute toxicityIn isolated cases, regulatory notifications have been cited that attributed some adverse events to synthetic formulations of THC (dronabinol) within broader lists of drugs, without this changing the overall relative safety profile of natural cannabis in terms of lethality.
In research, antagonists such as rimonabant (CB1) They can attenuate the effects of THC; naloxone/naloxonacin (opioid antagonists) and methyl-lycaconitine (an α7 nicotinic antagonist) have shown, in animal models, an impact on self-administration or motivational effects, which helps to Understanding neurobiology Of consumption.
Medicinal use and regulation
There are standardized pharmaceutical preparations containing THC and CBD (for example, oromucosal spray combinations authorized in certain countries) with specific indications such as Spasticity in multiple sclerosis or nausea from chemotherapy, always under prescription. The legal status of cannabis and its derivatives is heterogeneous by jurisdiction.
In terms of reproductive safety, THC has traditionally been classified into intermediate risk categories (e.g., category C), therefore its use in pregnancy requires clinical assessment of risks and benefits.
Tests, thresholds and technical variability
Screening tests detect the THC-COOH by immunoassay with confirmation by techniques such as GC-MS or LC-MS/MS. Cutoff thresholds and sensitivity vary between panels and laboratories, and the result is interpreted in conjunction with integrity tests (temperature, specific gravity, pH, creatinine) that They prevent adulteration.
Detection windows are not absolute: the same consumption pattern can yield different results depending on the technique, the laboratory, and the individual's physiological state. Therefore, experts recommend specific confirmations of positives and contextualize all findings with the clinical and occupational history.
Quick FAQ
Does exercise "cleanse" THC? It may modestly increase excretion through sweat and urine, but it does not "erase" in days what takes weeks in chronic consumers due to fat deposits.
Does drinking water dilute urine and help you test negative? Dilution is detected using integrity controls (e.g., creatinine, density), and an invalid result may be considered unfit or suspicious.
Do foods last longer in the body? They tend to generate more 11-OH-THC and longer-lasting effects, and can leave detectable metabolites for a little longer than an equivalent inhalation.
Sources and recommended readings
For further information on pharmacology, detection windows, and analytical guidelines, reviews and resources from national institutes and reference laboratories:
- National Institute on Drug Abuse: Fact sheets and materials on cannabis (effects, addiction and treatments).
- Drug Enforcement Administration: Substance Manuals and classification.
- National Substance Use Surveys (SAMHSA) with prevalence and trends.
- Toxicology laboratories: guides detection in urine, blood and saliva; time tables.
- Journal reviews (e.g., on detection in biological fluids) and recommended methods of International organizations for analysis of cannabis and derivatives.
- Studies on urinary elimination of THC-COOH in monitored abstinence and comparisons of hair vs. self-report in consumers of different levels.
- Articles on “detox kits” and risks, as well as clinical documents from DSM diagnosis in cannabis use disorders.
- MedlinePlus: Information on toxicology screens and their interpretation.
- Technical download: academic document related to detection and addictions.
It's important to have a clear understanding: the psychoactive molecule (THC) is transformed into metabolites such as THC-COOHwhich persist and allow for the detection of consumption for days or weeks; detection windows depend on the type of sample, the pattern of use, and the individual's physiology; "shortcuts" to circumvent tests are neither safe nor reliable; and, if consumption causes problems, there are effective therapeutic resources that combine medical and psychological support to restore balance.