Marijuana, also known as weed, cannabis or pot, is a drug that's derived from the cannabis sativa plant. Within the plant is a chemical known as tetrahydrocannabinol (THC), which produces a ‘high’ when someone smokes, ingests or vapes it.
UK drug statistics show that almost 30% of people aged 16 to 59 have taken marijuana at least once in their lifetime. Once you've taken the drug, the metabolites of THC remain in your system for days and weeks after you've taken the drug.
Various drug tests can be taken that are designed to detect these metabolites. Weed might be detected in your system for up to 90 days after you’ve taken the drug, depending on a number of factors, including:
Cannabis can be detected in your system using a drug test. How long it can be detected after you last used the drug can depend on the method of sampling.
After you last took the drug, weed can be detected in your blood for a day or two (48 hours), your saliva for 2 to 3 days (24-72 hours), urine for anywhere between 3 and 30 days, and hair follicles for up to 90 days.
Depending on the amount you've consumed and how often you generally take the drug, these figures can vary.
According to information from Drug and Alcohol Information and Support Ireland, cannabis is typically detectable in the blood for around 1 to 2 days after use.
However, the frequency of use can extend this significantly. Research published in Therapeutic Drug Monitoring indicates that in chronic users, cannabis can remain detectable in the blood for up to 25 days after the last use.
The Mayo Clinic Proceedings' Clinical Interpretation of Urine Drug Tests suggests that marijuana can be detected in urine from a few days to several weeks after your last use, depending on the frequency of use. General guidelines indicate:
MedlinePlus notes that urine testing is the most common method for detecting marijuana.
Saliva is often used in roadside drug tests for drivers. It can detect cannabis in the system between 24 to 72 hours after the last use.
THC enters hair follicles through the bloodstream, making hair tests another method for detecting cannabis. A hair test can reveal traces of the drug up to 90 days after your last use.
However, hair tests are generally considered less reliable than other methods. Exposure to second-hand marijuana smoke or physical contact with someone who has handled cannabis could potentially lead to a false positive.
| Location | Detection time |
| Blood | 24-48 hours |
| Saliva | 24-72 hours |
| Urine | 3-30 days |
| Hair follicle | Up to 90 days |
The time marijuana remains in your system depends on various factors. These factors tend to relate to how your body metabolises the drug, rather than the specifics of the test being used.
Once inhaled, THC from cannabis enters your bloodstream via your lungs (or via your liver if the cannabis was ingested).
Sometimes THC can also be stored in your organs or fatty tissues - meaning those with higher levels of fat molecules may metabolise THC more slowly.
THC then goes to your liver, where its metabolites are broken down. After this process, the THC and its metabolites will be excreted in your urine or stool.
It takes your body longer to metabolise larger quantities of THC, meaning the more cannabis you take the longer it will remain in your system.
There's nothing reliable you can do that would lead to weed being metabolised faster in your system. Some weed detox kits are available, which claim to help you dilute (and mask the dilution) of drugs in your system. However, these kits are known to be unreliable.
According to TalktoFrank, the effects of cannabis can be felt as little as 1 to 2 minutes after smoking it. When cannabis is ingested, it can take as long as 45 minutes to feel the effects. The common effects of THC include changes in your mood, impairing your inhibitions like sight and speech, and altering your sense of perception.
You might also develop other physical sensations such as anxiety, a dry mouth, increased heart rate and feeling sick of faint.
Generally, the ‘high’ you get from weed will last between 40 minutes to an hour or more.
Any short-term effects from cannabis, from the high it delivers to physical side-effects, tend to wear off after 1-3 hours. This can vary depending on the strength and drug, how much was taken and over what period.
After long-term use, cannabis can put you at risk of health problems and addiction. These may last for weeks, months, and years depending on the condition.
