How Long Does Weed Stay in Your Blood?

Though cannabis is legal in most of the United States, those who are employed by the federal government or otherwise obliged to undergo mandatory drug testing, aren’t at liberty to enjoy it when and how they like. Many factors can contribute to the duration of time in which THC stays in your blood, and each drug test is different.

Learn about the many tests used today, the amount of time cannabis can be detected in your body, and if you can quickly flush weed out of your system.

How Long Does Weed Stay in Your Blood?

Knowing how long cannabis stays in your system is useful information for anyone planning to take a drug test. But we must dive into how drug testing works to answer this important question. Since THC is the cannabinoid most associated with the cannabis plant’s psychoactive effects, it’s generally what drug tests are designed to detect.

However, contrary to popular belief, drug tests don’t actually test for the THC cannabinoid specifically, but rather how long its chemical by-products stay in your body in general. THC’s chemical by-products, known as metabolites, are chemical compounds formed by breaking down substances such as THC. The clinicians administering drug tests use the presence (and concentration) of metabolites to determine if and when THC was last used.

So, while marijuana itself may not remain in your blood for very long, those metabolites may remain detectable in your urine, saliva, or hair for much longer.

What Kind of Drug Tests Detect Cannabis?

Here’s a rundown of the most common types of drug tests and their generally accepted windows of detection:

  • Urine Test: The most common kind of THC test is the urine test. Designed to detect a THC metabolite known as (9-carboxy-THC), it’s considered relatively accurate and has the advantage of not requiring an invasive procedure such as a blood draw. Will one puff of weed be detected in a pee test? It’s unlikely, though not impossible.
  • Blood Test: This test is performed by drawing a blood sample and analyzing it for the presence of metabolites. How long is cannabis in your blood? Not very long. Usually, this type of test can only detect cannabis use within the last 24 hours. Heavy or chronic users may have cannabis metabolites that can be detected for several days after the last use, also depending on other individual factors like metabolism.
  • Saliva Test: A saliva test—also known as an oral fluid test—uses a swab to collect a sample; clinicians then analyze the saliva in your mouth for cannabis metabolites. It’s less common than a urine test, but it’s sometimes used by employers or law enforcement agencies. Generally, the most commonly cited detection window is 30 hours. In practice, most saliva tests can only determine if someone has used cannabis within the past 12 to 24 hours.
  • Hair Follicle Test: While hair tests are the least common type of drug test, they’re also the most sensitive and best at detecting long-term drug use. In some cases, these tests can indicate the presence of THC metabolites for up to 90 days or longer after the cannabis was consumed. Hair follicle tests are performed by taking a small amount of hair and testing its oil, which is usually transferred from the skin.

Testing for THC: Biological and Metabolic Factors

You can still have THC metabolites in your system anywhere from several weeks to several months after you last used cannabis. Exactly how long the cannabis stays in your system is very difficult to predict due to each person’s individual biological factors, but if you know what affects the length of metabolite retention, you can get a general idea.

How long THC metabolites remain in your blood depends primarily on these factors:

Frequency of Use

The most important factor to consider is how often you use cannabis. If you are a heavy or chronic consumer, you will tend to test positive for much longer than an occasional or rare cannabis user.

THC Content

The second element to consider is the strength of the cannabis products you use. Higher percentages of THC in your cannabis products or flower means that more THC is entering your system and, typically, means it’ll take for the body longer to clear it out and result in a negative drug test.

Fatty Tissue

THC binds to fat cells in the body, so the more fatty tissue you carry, the harder it will be to rid your body of the metabolites. This may result in you testing positive for THC for a longer period of time. This factor relates not only to our body mass index (BMI) but also to sex. Regardless of size and weight, women tend to have more fatty tissue than men.

Additionally, chronic cannabis use—especially of high-potency products—spurs our bodies to store more cannabis metabolites in fat cells, just as we store energy. However, as anyone who’s tried to diet knows, fat cells are harder to get rid of, and by extension, those metabolites tend to stick around for longer as well.


Each person’s metabolism—the rate at which they process energy—is unique, and some people will naturally metabolize THC and other compounds more quickly than others. People with faster metabolisms tend to eliminate metabolites more rapidly than those with slower metabolisms.

How can you tell if you have a fast metabolism? Signs of a fast metabolism may include a tendency to burn calories quickly, difficulty gaining weight, increased breathing rate, insomnia, and frequent sweating. By contrast, signs of a slow metabolism may include feeling tired, trouble losing weight, a constant craving for high-sugar and high-fat foods, and the experience of bloating and constipation.

Can One Puff of Weed Be Detected in a Drug Test?

While urine tests are most common and often considered the gold standard of drug testing, they’re not infallible. For one, even if you have been abstaining from direct cannabis use, false positives are not unheard of with urine testing. These tests also don’t indicate the amount of THC metabolites, merely their presence—for instance, if the purpose of the drug test was to demonstrate job performance impairment, a urine test might not pass a legal challenge.

Hair tests are considered the most sensitive, but will one hit of weed show up on a hair test? While it’s impossible to say with certainty, the chances are slim. Even this relatively sensitive type of test is generally regarded as a “lifestyle test,” meaning that it’s designed to indicate regular or chronic cannabis use.

As with other test types, a hair test can result in a false positive since it tests body oils. Some research suggests that THC present in skin oil (for instance, from contact with someone who used THC) may transfer to the hair, resulting in a false positive.

Can You Flush Weed From Your System?

If you do an internet search for “clean out cannabis metabolites,” you’ll find a number of “metabolite flushing” products on offer. Do any of them actually work? There’s not a ton of evidence that they do, but a couple of common-sense lifestyle strategies may help to flush weed from the system more quickly, but these haven’t been outright proven either:

  • Drinking lots of water
  • Consuming high-fiber
  • Regular exercise
  • Getting plenty of sleep

Strenuous exercise just before a drug test may help diminish the chances of a positive result, but there may be a risk to doing this. A challenging workout may help release any cannabis metabolites stored in fat cells, thus making them more detectable in the short term. If you choose the exercise route, we recommend you put in some hard workouts in the days leading up to the test but abstain the day of or immediately preceding the test.

What about hair cleansers? Some people who undergo regular drug tests swear by Zydot brand “Ultra Clean Detox Shampoo.” In fact, at least one clinical study determined its efficacy in removing drug metabolites. Though the shampoo didn’t eliminate the metabolites completely, it did reduce the concentration of THC markers by nearly a third.

Deepen Your Knowledge of Cannabis with Mission

At Mission, we believe knowledge is power. Visit our authoritative, science-based cannabis blog for more information. You’ll find articles on the intersection of cannabis and exercise, cannabis for sleep, and much more.

Still have questions about how long weed is in your blood, the different types of drug tests, or any other cannabis-related questions? Stop by any of our many locations, pick up your favorite products, and ask our friendly budtenders all your burning questions—we’re here to help!