How long weed stays in your system depends on the type of drug test and how often you use it. A urine test, the most common kind, can detect marijuana anywhere from 3 days to over 30 days after your last use. That wide range comes down to frequency of use, body fat percentage, and metabolism. Here’s what to expect for each test type and the factors that shift the timeline.
Urine Tests: The Most Common Screening
Urine tests don’t look for THC itself. They detect a byproduct your body creates when it breaks down THC, called THC-COOH. The standard screening uses a cutoff of 50 nanograms per milliliter (ng/mL). If you test above that level, a second confirmatory test is run at a stricter cutoff of 15 ng/mL.
General detection windows based on usage frequency:
- One-time use: 3 to 4 days
- A few times per week: 5 to 7 days
- Daily use: 10 to 15 days
- Heavy, prolonged use: 30 days or more
These are estimates. Some chronic users have tested positive beyond 45 days. The reason comes down to how your body stores THC, which is fundamentally different from how it handles alcohol or most other drugs.
Why THC Lingers So Long in Your Body
THC is fat-soluble. When you consume marijuana, your liver converts THC into metabolites, and some of those metabolites bind to fat cells throughout your body. They’re released slowly back into your bloodstream over days or weeks, then filtered out through urine. For an infrequent user, the half-life of THC is roughly 1.3 days, meaning half the substance is cleared in that time. For heavy users, the half-life stretches to 5 to 13 days. THC-COOH can remain stored in fat for over 30 days.
This is why a single weekend of use clears quickly, but months of daily use creates a deep reservoir of metabolites that your body takes weeks to fully eliminate.
Blood and Saliva Tests
Blood tests have the shortest detection window. THC enters the bloodstream within seconds of inhaling and peaks almost immediately, but blood concentrations drop rapidly. For occasional users, THC is typically undetectable in blood within 24 to 48 hours. Heavy users may test positive for up to a week, though this is less common.
Saliva (oral fluid) tests detect THC itself rather than a metabolite, and the window is short: up to 24 hours for most users, according to Cleveland Clinic data. The federal cutoff for an oral fluid screening is 4 ng/mL, with a confirmatory threshold of 2 ng/mL. These tests are increasingly used for roadside screening and workplace incidents because they’re better at capturing recent use rather than past use.
Hair Follicle Tests
Hair tests have the longest detection window by far. The standard protocol, used by major labs like Quest Diagnostics, analyzes the first 1.5 inches of hair from the root. Since head hair grows about half an inch per month, that sample covers approximately 90 days of history.
Hair testing is designed to identify a pattern of repeated use, not a single occasion. THC metabolites are deposited into the hair follicle through the bloodstream as the hair grows. The minimum hair length for a valid sample is about 1 centimeter. If your head hair is too short, collectors can use body hair from the chest, underarms, legs, or face, in that order. Body hair grows more slowly, so the detection window can actually be longer than 90 days.
Factors That Speed Up or Slow Down Clearance
Two people who smoke the same amount on the same day can test differently a week later. The biggest variables are body composition, metabolism, and genetics.
Because THC binds to fat, people with a higher body fat percentage have more storage space for metabolites. Someone with a lower body fat percentage and a faster metabolism will generally clear THC sooner. Your liver does the heavy lifting here, using a specific enzyme system to break down THC. Genetic variations in those enzymes make some people naturally fast metabolizers and others slow metabolizers, and there’s no easy way to know which you are.
Age matters too. Metabolic processes slow as you get older, which can extend clearance time. Hydration, physical activity, and overall liver and kidney health all play supporting roles, though none of them are reliable shortcuts. Exercising heavily right before a test can actually backfire by releasing stored THC from fat cells into your bloodstream.
Can CBD Products Cause a Positive Test?
Yes. Hemp-derived CBD products are legally allowed to contain up to 0.3% THC. That sounds negligible, but regular daily use of CBD oil, gummies, or tinctures can cause THC metabolites to accumulate to detectable levels over time. The problem is compounded by poor industry regulation. Independent lab testing and FDA reports have found CBD products containing significantly more THC than their labels claim. If you use CBD products regularly and face drug testing, this is a real risk.
False Positives From Other Substances
Initial urine screens can sometimes flag THC when there is none present. Common over-the-counter painkillers like ibuprofen and naproxen have been reported to trigger false positives, as has pantoprazole, a heartburn medication. This is one reason confirmatory testing exists. The second, more precise test specifically identifies THC-COOH and filters out interference from unrelated substances. If you’re taking any of these medications and receive a positive result, the confirmatory test should correct the error.
Detection Windows at a Glance
- Urine: 3 to 30+ days depending on usage
- Blood: 1 to 2 days (occasional), up to 7 days (heavy)
- Saliva: up to 24 hours
- Hair: up to 90 days
The single biggest factor across all test types is how frequently and how much you use. Occasional, low-dose use clears relatively fast. Daily, high-dose use over weeks or months creates a metabolite backlog that takes the longest to fully leave your system.