Drug tests for cannabis—also known as marijuana, weed, or pot—measure THC and its metabolites. THC can be detected in blood or saliva within 2–24 hours after use, while urine and hair tests can detect it from 1–90 days after the last use.
One of the primary components in cannabis is delta-9-tetrahydrocannabinol (THC). Drug tests identify THC and its by-products, which remain in your system long after the effects of weed have dissipated. These metabolites are fat-soluble, meaning they attach to fat molecules in your body, making it take longer for them to be eliminated, especially if you have a higher body fat percentage.
The detection window depends on the amount and frequency of cannabis use. Higher doses and more frequent use result in longer detection times. The type of drug test also affects detection duration. Blood or saliva tests usually have shorter detection windows, while urine and hair tests can detect cannabis use months after the fact, with the longest reported detection times exceeding 90 days.
Detection Windows for Different Cannabis Drug Tests
1) Urine Tests Urine testing is the most common method for drug testing. According to a 2017 review, cannabis can be detected in urine for the following durations after last use:
- Single use (one joint): 3 days
- Moderate use (4 times per week): 5–7 days
- Chronic use (daily): 10–15 days
- Chronic heavy use (multiple times per day): More than 30 days
2) Blood Tests Blood tests typically detect recent cannabis use or use within the last 2–12 hours. However, in cases of heavy use, it has been detected 30 days later. Chronic heavy use increases the detection period.
3) Saliva Tests THC can enter the saliva through exposure to secondhand smoke, but its metabolites are only present in saliva if you have personally smoked or ingested cannabis. Saliva testing has a short detection window and can sometimes detect same-day use. A 2020 review found that THC was still detectable in the oral fluid of frequent smokers 72 hours after use. THC may be detected in oral fluid longer than in blood after acute use. In areas where cannabis is illegal, saliva tests may be used for roadside testing.
4) Hair Tests Hair follicle tests can detect drug use for up to 90 days. Cannabinoids reach the hair follicles through small blood vessels and from sebum and sweat surrounding the hair shaft. Since hair grows about 0.5 inches per month, a 1.5-inch hair segment taken close to the scalp can provide a three-month timeline of cannabis use.
How THC Moves Through the Body and Breaks Down (Metabolizes)
When you smoke or ingest cannabis, THC is absorbed into the bloodstream. Some THC is temporarily stored in organs and fatty tissues and is broken down in the liver into over 100 metabolites, the most significant being 11-OH-THC and THCCOOH. Eventually, THC and its metabolites are excreted in urine and stool. The more THC metabolites in your body, the longer this process takes.
Factors Affecting THC and Metabolite Retention
Several factors influence how long cannabis metabolites stay in your system:
- Body Mass Index (BMI) and metabolic rate: These are related to how your body processes substances.
- Cannabis use factors: These include dosage, frequency of use, route of administration (smoking, dabbing, edibles, sublingual), and the potency of the cannabis.
Higher doses and more frequent use generally increase the time it takes to eliminate THC and its metabolites from your system. Ingested cannabis may remain in your system slightly longer than smoked cannabis, and more potent cannabis (higher in THC) may also extend this period.
Speeding Up THC Metabolism
There is little you can do to expedite the removal of THC metabolites from your system. Once THC is in your system, it takes time for your body to metabolize it. While exercising, eating a balanced diet, and staying hydrated may help slightly, they do not significantly speed up the process. Detox remedies and kits available online are generally unreliable and may involve drinking excessive water, which can be dangerous.
Onset and Duration of Cannabis Effects
The effects of cannabis appear almost immediately after smoking but may take 1–3 hours to peak when ingested. THC, the main psychoactive component, produces a “high,” causing altered senses, mood changes, difficulty with thinking and problem-solving, and impaired memory. Other short-term effects can include anxiety, confusion, decreased coordination, dry mouth and eyes, nausea, inability to focus, increased appetite, rapid heart rate, restlessness, and sleepiness. High doses can rarely cause hallucinations, delusions, and acute psychosis.
Regular use of cannabis may have additional effects on the mind and body. Research has shown mixed results, but cannabis use may increase the risk of cognitive impairments, cardiovascular diseases, respiratory illnesses, and mood disorders. Using cannabis during pregnancy can negatively affect fetal growth and development.
Duration of Cannabis Effects
Short-term effects typically subside after 1–3 hours. The duration of long-term effects is less understood, with some lasting days, weeks, or months after the last use. Certain effects may be permanent.
