Weed can be detected in your system for as little as 24 hours or as long as 90 days, depending entirely on the type of test. For the most common test, a urine screen, the window ranges from about 3 days for a single use to roughly 3 to 5 weeks for daily, long-term use. Your body fat percentage, metabolism, and how often you use all shift that timeline significantly.
Urine Tests: The Most Common Screen
Urine testing is the standard for most workplace and legal drug screens. These tests don’t look for THC itself but for a byproduct your body produces as it breaks THC down. That byproduct has a half-life of roughly 30 hours after a single dose, meaning it takes about a day and a half for your body to eliminate half of it. But with repeated use, the compound builds up in fatty tissue and releases slowly over days or weeks.
At the federal standard screening threshold of 50 ng/mL, here’s what the detection windows look like:
- Single or occasional use: 3 to 4 days after your last session. At a lower, more sensitive cutoff (20 ng/mL), this can stretch to about 7 days.
- Regular use (several times a week): 1 to 2 weeks.
- Daily, chronic use: Up to 21 days is typical at the lower cutoff. Under extraordinary circumstances involving years of heavy daily use, 30 days or slightly longer is possible, though uncommon.
If an initial screen comes back positive at 50 ng/mL, a confirmatory test is run using a stricter cutoff of 15 ng/mL. That more sensitive follow-up can extend the practical detection window by a few extra days compared to the initial screen alone.
Saliva Tests: A Short Window
Oral fluid tests detect THC itself rather than a metabolite, and they’re designed to identify recent use. Weed is generally detectable in saliva for up to 24 hours. The federal cutoff for an oral fluid screen is 4 ng/mL, with a confirmatory threshold of 2 ng/mL. Because the window is so short, employers increasingly use saliva tests when they’re more interested in whether you’re currently impaired than whether you used cannabis last week.
Blood Tests: Hours, Not Days
THC enters your bloodstream almost immediately after inhalation and peaks within minutes. Blood concentrations drop quickly, typically becoming undetectable within a few hours for occasional users. Heavy users may test positive for a day or two longer because THC stored in fat slowly leaks back into the blood. Blood testing is less common in workplace screening and is most often used in DUI investigations or medical settings where recent impairment is the question.
Hair Follicle Tests: Up to 90 Days
Hair testing has the longest detection window of any method. THC metabolites are deposited into hair follicles through the bloodstream and become locked into the hair shaft as it grows. A standard hair test covers the most recent 90 days of use. Because head hair grows at roughly half an inch per month, labs typically collect a 1.5-inch sample taken close to the scalp. Hair tests are better at identifying patterns of repeated use than catching a single session weeks ago.
Why Body Fat and Activity Level Matter
THC is fat-soluble, which makes it behave differently from most other recreational drugs. Instead of being flushed through your kidneys quickly, THC accumulates in fatty tissue throughout your body. It then re-enters your bloodstream gradually as fat cells release it. This is why two people who smoke the same amount on the same day can have very different detection windows.
People with a higher percentage of body fat tend to store more THC and release it more slowly. Physically inactive people clear it slower than active ones. Individuals with naturally slow metabolisms or certain health conditions that affect metabolism can also test positive longer than average. In a small percentage of cases, people test positive beyond the typical upper bounds for all of these reasons.
Edibles vs. Smoking
The method of consumption changes how quickly THC hits your bloodstream but doesn’t dramatically alter the overall detection window on a urine test. When you smoke, THC peaks in your blood within minutes and your body begins processing it right away. With edibles, absorption is slower and more prolonged, which can slightly extend how long metabolites are produced. The total amount of THC consumed matters more than the delivery method. A high-dose edible introduces more THC into your system than a few puffs, and more THC means more metabolite to clear.
Can Secondhand Smoke Cause a Positive Test?
Under normal conditions, no. A Johns Hopkins study tested this by sealing nonsmokers in a room with heavy cannabis smokers. When ventilation fans were running, the nonsmokers showed no meaningful effects and didn’t test positive. When the fans were turned off, creating what the researchers called “extreme” and “worst-case” conditions, some nonsmokers did produce detectable THC levels, and a few hit positive thresholds on standard drug tests. The lead researcher noted that those conditions couldn’t realistically happen to someone without them being fully aware of it. Casual exposure at a party or outdoors is extremely unlikely to trigger a positive result.
Detox Products Don’t Speed Things Up
A large market exists for drinks, supplements, and kits claiming to flush THC from your system faster. There is no scientific evidence that any of these products accelerate the rate at which your body eliminates THC metabolites. Your liver processes THC on its own timeline, and no supplement changes that. Drinking excessive water before a test can dilute your urine, but labs check for dilution and will flag or reject overly watery samples. You also cannot wash THC metabolites out of your hair with special shampoos.
The only reliable way to clear THC from your system is time. For occasional users, that means a few days. For heavy daily users, it can mean three weeks or more of abstinence before a urine test comes back clean.
Federal Workplace Testing in 2025
Despite shifting state laws and a December 2025 executive order directing the rescheduling of marijuana from Schedule I to Schedule III, federal workplace drug testing rules remain unchanged for now. The Department of Transportation has confirmed that marijuana testing continues under existing regulations, and safety-sensitive positions still require abstinence. Until rescheduling is formally completed, the same cutoffs and testing panels apply across all federally mandated screens.