Drug tests for cannabis — also known as marijuana, weed, or pot — measure THC and its metabolites. THC may be detected in blood or saliva as soon as 2-24 hours after last use. Urine and hair tests have a longer detection window, anywhere from 1–90 days after last use.
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 depend on how much cannabis you smoke or ingest, as well as how often. In general, 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 testing is the
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 (four times per week): 5–7 days
- chronic use (daily): 10–15 days
- chronic heavy use (multiple times per day): more than 30 days
Chronic heavy use increases the length of time that it can be detected.
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.
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 broken down in the liver. It has more than
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.
A number of factors affect how long cannabis metabolites stay in your system.
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, sublinguals)
- the overall potency
Higher doses and more frequent use
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.
There are weed detox remedies and kits available on the internet. Many require drinking a lot of water to dilute your urine, and then 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.
- altered senses, including sense of time
- changed in mood
- difficulty with thinking and problem solving
- impaired memory
Other short-term effects can include:
- decreased coordination
- dry mouth and eyes
- feeling sick or faint
- inability to focus
- increased appetite
- rapid heart rate
Smoking or ingesting weed on a regular basis may have additional effects on your mind and body.
- cognitive impairments, such as memory loss
- cardiovascular diseases, such as heart disease and stroke
- respiratory illnesses, such as bronchitis and lung infections
- mood disorders, such as depression and anxiety
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.
How long does THC stay in the body?
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
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.