Drug tests for cannabis — also known as marijuana, weed, or pot — measure THC and its metabolites. THC may be detected in blood or saliva 2–24 hours after use. Urine and hair tests have a longer detection window from 1–90 days after the last use.

One of the most abundant components in cannabis is a chemical substance called THC, which stands for delta-9-tetrahydrocannabinol.

Drug tests for cannabis measure THC and its by-products or metabolites. These metabolites remain in your system long after weed’s effects have worn off.

Cannabis metabolites are fat-soluble, which means they bind to fat molecules in your body. As a result, it can take some time for them to leave your system, particularly if you have more fat molecules in your body.

The detection window depends on how much cannabis you smoke or ingest, as well as how often. Higher doses and more frequent use are associated with longer detection times.

The type of drug test used also plays a role. Cannabis metabolites usually have a shorter window of detection in blood or saliva samples.

Urine and hair samples may show evidence of cannabis use several months after the fact. The longest reported detection times are more than 90 days.

Urine tests

Urine testing is the most common drug testing method.

While detection windows may vary, a 2017 review suggests that cannabis may be detectable in urine for the following amounts of time after last use:

  • single use (one joint, for example): 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

Blood tests

Blood tests typically detect recent cannabis use or use that has occurred within the last 2–12 hours. However, it’s been detected 30 days later in heavy use cases.

Chronic heavy use increases the length of time that it can be detected.

Saliva tests

THC can enter the saliva through exposure to secondhand cannabis smoke. However, its metabolites are only present in saliva when you have personally smoked or ingested cannabis.

Saliva testing has a short window of detection and, in some cases, may detect same-day cannabis use.

A 2020 review found that THC was still detected 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 jurisdictions where cannabis is illegal, oral fluid may be used for roadside testing.

Hair tests

Hair follicle tests can assess drug use for up to 90 days. After use, cannabinoids reach the hair follicles via small blood vessels and from sebum and sweat surrounding the hair shaft.

Since hair grows approximately 0.5 inches per month, a 1.5-inch hair segment taken close to the scalp can provide a timeline of cannabis use over the past 3 months.

THC is absorbed by the bloodstream when you smoke or ingest cannabis. Some THC is temporarily stored in organs and fatty tissues.

THC is broken down in the liver. It has more than 100 metabolites, but the most significant ones are 11-OH-THC (11-hydroxy-delta-9-tetrahydrocannabinol) and THCCOOH (11-nor-9-carboxy-delta-9-tetrahydrocannabinol).

Eventually, THC and its metabolites are excreted in urine and stool. The more THC metabolites you have in your body, the longer this process takes.

Several factors affect how long cannabis metabolites stay in your system.

Some factors, such as body mass index (BMI) and metabolic rate, aren’t related to the drug itself but to how your body processes it.

Other factors are related to cannabis and how you use it. This includes:

  • how much you take (dose)
  • how often you use (frequency)
  • the route of administration (smoking, dabbing, edibles, sublingual)
  • the overall potency

Higher doses and more frequent use tend to increase the amount of time it takes to eliminate THC and its metabolites from your system.

Cannabis that’s ingested may remain in your system slightly longer than cannabis that’s smoked. More potent cannabis, which is higher in THC, may also stay in your system for longer.

There isn’t much you can do to speed up the amount of time it takes for THC metabolites to leave your system.

Once THC has entered your system, your body needs time to break it down. Exercising, eating a balanced diet, and staying hydrated may help, but not drastically.

There are cannabis detox remedies and kits available on the internet. Many require drinking water to dilute the urine and using herbal supplements such as creatinine or vitamin B12 to mask the dilution.

These kits don’t work reliably, and drinking large quantities of water in a short period of time can be fatal.

Effects appear almost immediately after smoking cannabis. However, it may take 1–3 hours for effects to peak when cannabis is ingested.

THC, the key psychoactive component in cannabis, produces a “high.” Common effects include:

  • altered senses, including a sense of time
  • changes in mood
  • difficulty with thinking and problem-solving
  • impaired memory

Other short-term effects can include:

In rare cases, high doses of cannabis can cause hallucinations, delusions, and acute psychosis.

Smoking or ingesting cannabis on a regular basis may have additional effects on your mind and body.

While study findings have been mixed, using cannabis may put some people at an increased risk of developing:

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

Short-term effects start to taper off after 1–3 hours. Researchers don’t know how long the effects of chronic cannabis use last.

Long-term effects may last days, weeks, or months after the last use. Some effects may be permanent.

How long does THC stay in the body?

THC metabolites stay in the body for at least 1–30 days after use. Regular cannabis users may have elevated THC levels even after a period of abstinence.

Will a hit of weed show up on a urine test?

A 2017 review found that a person who has used cannabis just once may receive a positive urine test for up to 3 days after last use.

Will weed show up in any urine test or sample?

No. Only urine tests designed to detect THC metabolites will show cannabis use.

How long does it take to detox from cannabis?

It depends on the frequency of use. Chronic heavy use may still result in a positive test for THC metabolites on a urine test more than 30 days after the last use.

THC and its metabolites may stay in your system anywhere from several days to several months after you last use cannabis.

Different drug tests for cannabis have different detection windows. In general, detection time will be longer with a higher dose and more frequent cannabis use.

Testing for THC and its metabolites can only determine whether cannabis has been used within a given window of time. Drug tests aren’t a measure of current impairment.