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How long does Marijuana stay in your system?

Medically reviewed by Carmen Fookes, BPharm. Last updated on Apr 17, 2019.

Official Answer

It varies according to usage

It is impossible for anyone to accurately state the length of time it would take for somebody to test clean for marijuana in a drug test. This is because there are many different variables that impact on the rate that marijuana is both metabolized and excreted (see below).

An estimate of marijuana detection time after last usage is as follows:

Usage Estimate of detection time
One time only 4-8 days
2-4 times per month 11-18 days
2-4 times per week 23-35 days
5-6 times per week 33-48 days
Daily usage 49-70 days after last use*

*Occasionally, some chronic users with a high tolerance may eliminate THC as fast as a one-time user.

We can give an estimate of the amount of time marijuana remains in the body, but the most reliable way is to test yourself twice weekly until your first, morning urine sample tests clean. However, even this is not 100% foolproof because home drug detection kits have a higher upper limit of detection (usually 50 ng/mL) compared to some other medical testing kits. This means you may test negative, but a laboratory test may still show marijuana in your system.

Note that charts, graphs, or computer programs that claim to be able to predict how long it will take you to test drug-free, are essentially useless at doing this, even though they may say otherwise.

What is delta-9 THC?

Marijuana is produced by the cannabis sativa plant. Cannabis sativa contains over 421 chemicals including 61 different cannabinoids, of which delta 9-tetrahydrocannabinol (delta-9 THC) is considered the most psychoactive. Delta-9 THC has a thick, sticky consistency (somewhere between a solid and a liquid) and is easily vaporized. It readily dissolves into lipids and fats, and once in the body gets deposited in fatty (adipose) tissue, and in the liver, lungs, and spleen.

Delta-9 THC undergoes metabolism in the liver to another psychoactive compound, 11-OH-THC, and then further metabolism to the inactive THCCOOH. CYP2C9 and CYP3A4 are major enzymes involved in this metabolism and both enzymes show genetic variation – this means that some people will metabolize THC faster than normal, whereas others will metabolize it slower than normal.

What variables impact on the time Marijuana stays in your system for?

Individual variables that play a role in how long marijuana stays in your system for and detection times include:

  • Body fat: People with more body fat will retain THC for longer. Skinny users have fewer places to store THC.
  • Fluid intake at the time of the test.
  • Genetics: Fast metabolizers will excrete THC rapidly.
  • How frequently you exercise.
  • Method and frequency of usage: Infrequent users clear THC faster than chronic users.
  • Type of detection test used (blood, hair, saliva, or urine).
  • Your general health: Many medical conditions impact on how your body retains, stores, and metabolizes marijuana.
  • Other drugs taken: Many drugs interact with CYP2C9 and CYP3A4 enzymes.
  • The potency of the marijuana and your tolerance to it can also have an impact.

What are the different ways Marijuana can be tested for?

Firstly, it is important to understand the difference between qualitative and quantitative testing.

Qualitative testing tells you if a substance is there or not.

It does not tell you how much of the substance is there. There will be a cut off point for detection. For example, the Alere DDs 2 Mobile test system used roadside by law enforcement agencies has a cut off level for Delta-9-THC in saliva of 25 ng/ml. Research has shown that this testing system is 97.5% accurate at this cut off (this means that more than 97 people will accurately test positive out of 100 people who have used marijuana in the past 24 hours).

Quantitative testing measures the actual quantity of a substance.

This type of testing is more expensive and time-consuming than qualitative tests and is normally reserved for people who have tested positive in a qualitative test. It needs to be done in a laboratory and is used when a more defined value is needed, say, for prosecution. Quantitative testing can detect minute quantities of a substance, far below the cut off point in a qualitative test. A series of quantitative tests can determine if drug usage is ongoing or has stopped.

The most common ways marijuana can be tested for is in urine, saliva, blood, or hair. Most testing practices look for the presence of THCCOOH which has a much longer half-life (the time it takes for 50% of the substance to be excreted) than delta-9 THC. The half-life of THCCOOH is 20-57 hours in occasional users compared to 3-13 days in regular users.

Estimated periods of detection of the marijuana metabolite THCCOOH

Test Type Detection period (estimated)
Blood test 36 hours
Some reports suggest up to 7 days with chronic use (>3 months)
Hair test Cannot detect first-time drug use in the previous 7-14 days
Every 1cm of hair length represents a one-month window of detection
Detection period depends on hair length but generally 90 days
Saliva test Up to 34 hours
Urine test 1-4 days
Some reports suggest up to 70 days with chronic use (>3 months)

A false-negative is when the test result is negative for a substance, but the person has been using the substance. A false-positive is when the test result is positive for a substance, but the person hasn’t been using the substance.

Can second-hand marijuana smoke make you fail a drug test?

For kits that detect at the 50 ng/ml level the circumstances would have to be extreme, for example, if you were in a closed car full of marijuana smokers for a couple of hours and you were drug tested the next day. If you are a non-smoker in a ventilated area where other people are smoking marijuana you are generally safe.

Official answer: It varies according to usage It is impossible for anyone to accurately state the length of time it would take for…

How Long Does Weed Stay In Your System?

So how long does weed stay in your system? It depends on which system we’re talking about. From a certain perspective, humans appear hard-wired for cannabis. We have an endocannabinoid system throughout our body with receptors that perfectly fit the cannabinoids we ingest when we consume weed. And our bodies process those cannabinoids in a variety of ways, producing byproducts that can linger for a long time.

Overview: How Long Does Weed Stay In Your System?

Whether you’re new to cannabis and curious about how long the effects last and how long weed stays in your system, or facing a drug screening of some kind, knowing the specific ways weed interacts with your body and where signs of your using it show up is valuable information.

We’ll answer the perennial question—how long does weed stay in your system?—by taking a look at the four parts of the body that betray the signs of marijuana use.

But before diving in, let’s put the answer as simply as possible.

Remember, it’s technically the psychoactive, high-producing THC that makes your weed illicit, and your use of it illegal. And that illicit chemical is rapidly metabolized by your body when you smoke weed.

The process takes a little longer if you ingest cannabis, but the result is practically the same. You don’t stay high for days at a time because your body quickly processes all the psychoactive compounds you inhaled or ate.

But the byproducts of that process, called ‘metabolites,’ can stay in your fatty tissue for a long time. They’re not active, of course, but they’re telltale signs of previous cannabis use.

So again, how long does weed stay in your system? It depends what the system deals with, THC or its waste metabolite, THC-COOH.

If the system deals with active, or delta-9 THC, weed doesn’t stay around for very long. But if the system deals with eliminating inactive THC-COOH, weed sticks around for a longer time.

How Long Does Weed Stay In Your Blood?

Let’s start with the system that shows signs of weed for the shortest amount of time. That’s your circulatory system, or more specifically, the blood flowing through it.

THC and other active cannabinoids have to make it into your bloodstream to take effect. When you smoke, that happens via your lungs. When you ingest weed, that happens through your stomach.

In other words, your blood is where potent, active cannabinoids make their way to your brain, kicking off the euphoric sensations of being high, or the therapeutic effects in the case of cannabidiol (CBD).

Your body rapidly metabolizes, breaks down those active cannabinoids in the blood. And that’s why signs of weed use don’t stay in your blood for very long.

Hence the reason why companies or law enforcement will take blood tests after workplace or traffic accidents because it would reveal that someone was likely intoxicated with cannabis when the sample was taken.

Specifically, weed (i.e. THC) stays in the blood for one to two days after a single use. If you smoke multiple times or regularly or multiple times daily, weed will stay in your blood for up to a week after your last session.

How Long Does Weed Stay In Your Saliva

Saliva is virtually tied with blood in terms of the time span weed sticks around in it. No wonder a mouth swab drug test looks for the same active THC blood tests do.

Delta-9 THC, the psychoactive kind, coats the inside of your mouth and gets soaked up by your saliva glands after you smoke. If you eat edibles, your exposure is somewhat reduced, but you’re still chewing the decarbed cannabis in your cookie.

This THC doesn’t make it into your bloodstream in any significant quantity. It just stays in your saliva until you swallow enough of it to purge your mouth of the signs of your scandalous cannabis habit.

Therefore, drinking lots of water, brushing your teeth, using mouthwash, and eating fatty foods—THC bonds to fat—can help you get rid of THC in your mouth faster.

Specifically, THC will stay in your saliva for one to two days after your last puff. If you’re worried that you smoke a lot, or if your weed is more potent, traces of THC could linger up to a week, max.

How Long Does Weed Stay In Your Urine

As you can see, your body is naturally eager to absorb and process psychoactive THC and other active cannabinoids. (Drug tests, by the way, are only looking for THC.) So those chemical compounds of weed don’t stay in your system very long.

But the byproducts of THC, which are evidence of prior use, are also fat-soluble. In other words, THC metabolites bond to fatty tissues, and this causes the body to take some time expelling them.

So technically speaking, ‘weed’ doesn’t stay in your urine, THC-COOH does. And it’s totally inactive, meaning you’re not still under the influence of cannabis despite the presence of this chemical in your system.

Since the presence of cannabinoid metabolites in the body is entirely dependent on a person’s particular traits, it’s hard to answer definitively, how long does weed stay in your system?

Suffice to say, the amount of time evidence of cannabis use stays in your urine largely depends on how often you smoke up. Other factors, like your body mass index, your metabolic rate, and how hydrated you are also play a role.

Summing up the research we examined, this table can help you determine the average time weed will stay in your renal system.

  • 1-time use: clean in 5-8 days
  • 2-4 times a week: 11-18 days
  • 5-6 times a week: 33-48 days
  • Daily use: 50-65 days, up to 77

Cleanse Using a Detoxification Program

If you have at least seven days before your test, a detoxification program will speed up the body’s natural cleansing process and completely rid your body of the THC in your system in about a week. These programs also come with home testing kits to verify you are clean.

Cleanse the Same Day

If your test is coming up sooner, certain detox drinks are known to flush your system the same day you drink them keeping you clean for a period of four to six hours.

How Long Does Weed Stay In Your Hair

Although there are plenty of myths and misconceptions circulating about hair drug tests, they’re feared by weed users for good reason.

Evidence of cannabis consumption stays in your hair for longer than any other system in your body. In fact, hair follicle testing can reveal cannabis use up to years prior.

But in terms of common testing procedures, hair follicle tests are typically looking for cannabis use back 90 days.

One rumor is that drug test kit administrators or police will cut off the tips of your hair for a drug test. But that wouldn’t be very conclusive at all.

Instead, hair follicle tests take a head hair from the root to 1.5 inches of hair. Testers discard the rest of the hair.

Human head hair grows, on average, at a rate of about .5 inches per month. So 1.5 inches equals about three months of hair growth. If you took the end of a foot-long hair, you’d be able to detect weed use back two years!

Body hair, which grows more slowly than head hair and isn’t replaced as often by new hairs, may betray prior weed use back even further.

A body hair of the same length could show weed use back 180 to 360 days. At the moment, however, there are no conclusive studies verifying this.

So weed stays in your hair for a long time. But it doesn’t show up in one time or occasional users. Instead, hair testing reveals a chronic habit of marijuana consumption.

For regular cannabis users, this is definitely case for alarm. Once THC makes its way to the follicle and ends up in the hair strand, it’s there forever.

Of course, you could answer how long does weed stay in your system with the answer, not another second. All you have to do is shave off all of your hair.

The Final Answer: How Long Does Weed Stay In Your System?

The short-lived effects of weed don’t prevent evidence of marijuana consumption from lingering in your system. Of course, this doesn’t mean that you’re high for as long as those chemicals exist in your body. But it does mean you’re at risk of failing a drug test.

So how long does weed stay in your system? When it comes to saliva and blood, where active THC resides, weed stays in the body for a week, tops. But with urine, weed stays in your system much longer. And with hair, it’ll stay with you forever. Or at least until you cut that hair off!

The human body is a complex machine. And cannabis interacts with it in complex, dynamic ways we don't yet fully understand.