How Long Does Weed Stay in Your System?

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Tests for cannabis — commonly called marijuana, weed, or pot — look for THC and its breakdown products. THC may be found in blood or saliva within 2–24 hours after use. Urine and hair screenings typically reveal use over a longer span, ranging from 1–90 days after the last exposure.

A primary active ingredient in cannabis is delta-9-tetrahydrocannabinol, commonly abbreviated as THC.

Drug screenings target THC and its metabolites. These breakdown products linger in the body well after the acute effects of cannabis subside.

Because cannabis metabolites are lipophilic (fat-loving), they attach to fatty tissues in the body. Consequently, they can take longer to clear, especially in individuals with greater body fat stores.

How long metabolites remain detectable depends on the amount consumed and the frequency of use. Larger amounts and more regular use correlate with extended detection periods.

The specific testing method also matters. THC metabolites are usually detectable for a shorter period in blood or saliva specimens.

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What are the detection windows for different cannabis tests?

Urine tests

Testing urine is the most frequently used approach for drug screening.

Although detection ranges vary, a 2017 review indicates cannabis may be found in urine for the following approximate durations after last use:

• single use (one joint, for example): 3 days
• moderate use (about 4 times per week): 5–7 days
• chronic use (daily): 10–15 days
• chronic heavy use (several times daily): over 30 days

Blood tests

Blood testing generally detects recent cannabis consumption, typically within the past 2–12 hours. In heavy users, however, THC has been observed as late as 30 days after use.

Frequent heavy consumption lengthens the time THC remains measurable in blood.

Saliva tests

THC can appear in saliva after exposure to secondhand smoke, but metabolites generally show up in oral fluid only after the person has actively smoked or consumed cannabis.

Saliva testing has a relatively brief detection window and can sometimes identify same-day use.

A 2020 review reported THC detectable in the oral fluid of frequent smokers up to 72 hours post-use. After acute use, oral fluid may retain THC longer than blood.

Where cannabis remains prohibited, oral fluid tests are often used for roadside screening.

Hair tests

Hair follicle tests can reflect drug use for as long as 90 days. After consumption, cannabinoids reach hair follicles via small blood vessels and from sweat and sebum surrounding the hair shaft.

Because hair grows roughly 0.5 inches per month, a 1.5-inch sample cut close to the scalp can map cannabis use across the prior three months.

How is THC absorbed, distributed, and metabolized?

When you smoke or ingest cannabis, THC is absorbed into the bloodstream. Some THC temporarily accumulates in organs and fatty tissues.

The liver metabolizes THC. Although it forms over 100 metabolites, the main ones are 11-OH-THC (11-hydroxy-delta-9-tetrahydrocannabinol) and THCCOOH (11-nor-9-carboxy-delta-9-tetrahydrocannabinol).

Ultimately, THC and its metabolites are eliminated via urine and feces. The greater the amount of stored THC metabolites, the longer elimination will take.

Which factors influence how long THC and metabolites persist?

Multiple factors affect how long cannabis metabolites linger in your body.

Some influences, such as body mass index (BMI) and metabolic rate, relate to individual physiology rather than the drug itself.

Other determinants concern cannabis and usage patterns, including:

• amount consumed (dose)
• frequency of use
• route of administration (smoking, dabbing, edibles, sublingual)
• potency of the product

Larger doses and more frequent use usually prolong the time required to rid the body of THC and its metabolites.

Ingested cannabis may remain detectable slightly longer than smoked cannabis. Products with higher THC concentrations may also persist longer in the system.

Can you speed up metabolism of THC and its breakdown products?

There are few reliable ways to hasten elimination of THC metabolites from the body.

Once THC is in your system, your physiology needs time to process it. Exercise, a healthy diet, and good hydration might help modestly, but they won’t produce dramatic effects.

Numerous detox products and kits claim to cleanse cannabis from the body. Many instruct users to drink lots of water to dilute urine and take herbal supplements or additives like creatinine or vitamin B12 to mask dilution.

These methods are unreliable, and excessive water intake in a short period can be hazardous or even lethal.

When do cannabis effects start?

Effects begin almost immediately after smoking. When cannabis is eaten, it may take 1–3 hours for effects to peak.

THC, the main psychoactive ingredient in cannabis, causes a “high.” Typical effects include:

Other transient effects can involve:

In uncommon situations, very high doses may trigger hallucinations, delusions, or acute psychotic episodes.

Regular smoking or ingestion can have further consequences for mental and physical health.

While research results vary, cannabis use may raise the risk for some individuals of developing:

Using cannabis during pregnancy can adversely affect fetal growth and development.

How long do cannabis effects last?

Short-term effects typically start to subside after 1–3 hours. The duration of effects from long-term cannabis use is less well understood.

Longer-lasting effects can persist for days, weeks, or months after stopping. Some consequences may be permanent.

Frequently asked questions

How long does THC remain in the body?

THC metabolites can remain in the system for at least 1–30 days after use. People who use cannabis regularly may show elevated THC levels even after stopping for a while.

Will a single puff of weed show up on a urine test?

A 2017 review found that someone who used cannabis only once could test positive in urine for up to three days after that use.

Do all urine tests detect cannabis?

No. Only urine assays specifically designed to find THC metabolites will indicate cannabis use.

How long does it take to detox from cannabis?

Detox timing varies with usage patterns. Heavy chronic users may still test positive for THC metabolites on urine tests more than 30 days after their last use.

The bottom line

THC and its metabolites can persist in your body for anywhere from several days to multiple months after last using cannabis.

Different testing methods have distinct detection windows. In general, higher doses and more frequent use extend the time cannabis can be detected.

Tests for THC and its metabolites can indicate whether cannabis was used within a specific timeframe, but they do not measure current impairment.