Updated on October 12, 2018.
Medical content reviewed by Dr. Joseph Rosado, MD, M.B.A, Chief Medical Officer
Cannabis is a complex plant made even more intricate by its many different strains. There are three basic types of cannabis plants — indica, sativa and hybrids. Each kind of cannabis contains a different combination and balance of active compounds called cannabinoids. There are at least 113 different cannabinoids that we know of, and still more to discover.
Tetrahydrocannabinol (THC) is one of the primary cannabinoids found in cannabis plants. THC is responsible for the psychoactive properties of marijuana, and it can be balanced by other compounds in the plant to have different degrees of effectiveness.
THC mimics a chemical messenger found naturally in your brain. The brain recognizes the THC and responds to it. When THC attaches to the receptors in your brain, it blocks the natural chemicals from completing their messages. Instead, the chemical balance in your brain shifts and messages are affected.
When the THC leaves the brain, the chemical balance returns to normal. You experience restored coordination, and memory and the natural brain messenger system resumes. Accurate sensory messages replace the ones created by the THC.
How Long Do the Effects of THC Last?
THC affects your brain while you’re consuming marijuana and for up to a few hours afterward. Through continual dosing, you could theoretically maintain the effects indefinitely. The amount of time it takes for cannabis to make changes to your brain chemistry and how long it lasts is dependent largely on how you consume it.
Smoking marijuana sends THC to your brain very quickly. The smoke enters your lungs and absorbs into your bloodstream. Some of the cannabis moves directly through the cell walls in your sinuses into your brain.
Topical cannabis products have a quick effect on the area of application, but never make it to your brain. Topicals are absorbed through the skin and begin to work on the nerves in the area almost immediately. You won’t get that euphoric feeling from topical marijuana products, aside from the happiness you feel when your pain goes away.
Concentrated cannabis products like tinctures get into your bloodstream and move to your brain quickly if you administer them sublingually. A couple drops under your tongue will kick in rapidly to relieve pain and reduce nausea. The marijuana absorbs through the mucous membrane in your mouth directly into the bloodstream.
The longest lasting effects come from marijuana products that are swallowed, such as edibles and beverages. These must travel through the digestive system before they reach the brain, so it takes longer for them to take effect. In turn, the high lasts longer than that of inhaled products.
The effects from edibles are also typically enhanced compared to smokable or concentrated marijuana products. On their way through the digestive system, edible marijuana products pass through the liver. In the liver, the effects of marijuana concentrate, so when they reach the brain, the effect is stronger. Properly dosing with edible products is challenging because of the time lapse and the concentration effect.
How Long Can THC Be Detected?
It’s easy to assume that when you stop feeling the effects of marijuana, it’s out of your system. Though it may no longer be working on your brain, marijuana remains in your body for a long time. This can become a problem when it comes to drug testing.
Several variables determine how long cannabis stays in your system. A heavy user, for example, will maintain detectable levels of THC a lot longer than someone who has only used it once or twice.
Other variables include:
Means of consumption
History of usage
Tolerance for marijuana
Detecting THC in your body is also partially dependent on the type of test administered. THC will remain detectable in different parts of your body for varying amounts of time. Marijuana can only be detected in your saliva for up to 12 hours, while a hair test could show traces of THC for as long as 90 days.
The most common test for THC is a urine test. If you’re dosing with medical marijuana on a regular basis, you may test positive for THC in a urine test for up to 30 days after you stop using it. If you’re just an occasional user, your urine should be clean after about three days.
Blood tests can also be performed to check for the presence of THC. Within two days of your last marijuana use, your blood may test positive. After that, there should not be any detectable THC in your bloodstream. For frequent users of heavy doses of cannabis, it can take up to seven days to pass a blood test.
Even after a blood test cannot detect THC, traces can still show up in a hair test. Hair tests are not often used because they’re lengthier and more expensive. However, they’re very accurate and can show a pattern of marijuana usage for months after the last dose. Traces of THC are deposited on the hair shafts from the blood vessels in your scalp and remain there as the hair grows out. This method can even provide a timeline of usage.
In general, the amount of time marijuana is going to remain in your system is just speculation. There’s no way of truly knowing if a drug test will detect THC in your system in advance. The only real way to be sure there’s no THC in your system is to abstain from using marijuana products.
When trying to figure out how long THC stays in your system, there’s no perfect formula. And, different factors may alter the number of days THC will show up in a blood, urine or another drug test.
On average, individuals who smoked cannabis in the last:
Thirty to 45 days can fail a THC urine drug test
Sixty to 75 days can fail a cannabis blood test
There are distinct rates at which individuals who smoked cannabis break their THC levels down in their bodies. The date ranges of the risk of failing a cannabis drug test can range in THC levels detected in blood or urine and the length of use.
How Long Does THC Stay in Your Blood?
How long pot stays in your bloodstream is determined by:
The amount you use
The amount of THC stored in your fat cells
The amount and frequency of exposure
Many individuals know THC can stay in the bloodstream by hiding in fat cells then over time release fluctuating levels of THCCOOH, a THC metabolite.
When you consume medical weed, bloodstream levels of THC rise temporarily. Your blood carries the THC to your brain and other body organs, where the compounds start interacting with your cannabinoid receptors, causing short-term euphoria.
THC stimulates neurons in the reward system of your brain to release dopamine and induce the pleasurable “high” linked with cannabis. Euphoric sensations linked with THC include:
Changes in mood
Altered perception of time and physical sense
Impaired body movement
Feelings of relaxation and creativity
When you smoke or vape medical cannabis, the short-term effects come on within seconds and peak within a few minutes. Depending on the potency of the herb and your metabolism, the effects can last anywhere from one to three hours.
When you ingest medical cannabis, such as with edibles, the effects are delayed by digestion and take between 30 minutes to two hours to take hold after consumption. You experience THC’s effects for a prolonged duration when ingested due to continued slow absorption.
You can only detect THC itself in the bloodstream for a brief period. Your body rapidly metabolizes THC, modifying it into a minimum of 80 metabolic byproducts.
It generally remains detectable for up to three days after a single use. In regular users, THC can stay for up to 30 days in the bloodstream after the last use. And, even though the levels of THC drop substantially after several days, THC consumption can still be detected in your system in other ways.
How Long Does THC Stay in Your Urine?
Urine drug tests can’t show if you were high at the time of your testing or when the last time was that you smoked. They’re trying to detect if your body is still trying to eliminate the THCCOOH from your last cannabis session.
Since a drug test is highly dependent on all of your body’s complex processes involved in your metabolism, it’s no surprise it’s impossible to provide a straightforward and simple answer to the question — how long does THC stay in your system?
There are some influential factors, including:
1. Dose of THC
Researchers believe around 15 to 20 percent of a THC dose is eliminated when the user urinates. So, the stronger the pot is, the more metabolites will be present in the urine. This also explains how the administrators of the test can correlate the little amounts they detect with a real marijuana dose.
2. Use Habits
As expected, chronic users are susceptible to THC urine detection longer than individuals who use the herb occasionally.
A person who uses cannabis one time will have clean urine in around five to eight days. When smoking several times a week, your urine should be clean in approximately two weeks. Smoke daily and you’re looking at about one to two months to rid your system entirely of THCCOOH.
One comprehensive study reported daily use habits of one subject took 77 days before they were able to provide 10 consecutive clean tests.
While not set in stone, the following timeframes can give you an idea of average detection windows.
Use one time: clean in five to eight days
Use two to four time a week: clean in 11 to 18 days
Use five to six times a week: clean in 33 to 48 days
Use every day: clean in 50 to 77 days
3. Physiological Factors
With your body, two factors play a significant role in the length of time THC stays in your urine.
First, there’s your metabolic rate — you’ll excrete THCCOOH quicker with a higher metabolism.
Second, there’s your hydration level. The more fluids you drink, the more urine you produce, and the faster THC leaves your body.
4. Ingested or Inhaled
How long does THC stay in your urine after consuming edibles compared to vaping or smoking marijuana?
THC stays in your urine a little longer when you consume edibles — from a few hours to another day. But, this isn’t a substantial enough degree to make a huge difference in your test outcome.
What this means is both THC dose administration methods will put enough THCCOOH in your urine that you’ll fail a urine test.
However, because of how your body processes THC, when eating it, it converts to its 11-hydroxy-THC psychoactive metabolite and then converts from there into the inactive THCCOOH, which is what the test detects. Because of this, edibles can put you at a longer risk compared to vaping or smoking cannabis based on your use habits.
There are all sorts of inadequacies and shortcomings in urine drug tests. But they’re excellent for revealing whether you consumed marijuana — in any form — at some point in the past. For employers who have a zero tolerance policy, this is enough to move on to another candidate or fire you if you’re currently working.
Medical Marijuana and Drug Tests
It’s not easy to hide marijuana use, and medical marijuana programs reduce the need to do so. By following the guidelines of the medical marijuana program in your state, you’re protecting yourself from negative consequences and ensuring access to the medicine you need.
Depending on your situation, it could be important to let your employer know about your medical need for cannabis products. Though employers still operate under federal law and can enforce any consequences in their anti-drug policy even if you’re using it medically, most have policies that favor full disclosure. It’s a decision you need to make for yourself, but understand that beating a drug test when you’re a regular marijuana user is almost impossible.
THC in Drug Tests
CBD, THC and their metabolites are fat-soluble and accumulate throughout your body in fat reserves. They then begin releasing slowly over time, leading to a considerably longer time-frame for your body to purge itself of cannabis traces compared with other types of drugs, particularly for chronic users.
While there are advantages with each drug test, urine tests seem to be the most chosen ones by employers and the sole test the Substance Abuse and Mental Health Services Administration (SAMHSA) recommends. The SAMHSA sets drug testing standards for government employees. Urine tests, like hair tests, don’t measure the amount of THC directly present, but instead the THCCOOH metabolite levels.
A qualitative no/yes with a usual 50 ng/mL cutoff.
Send it off to be confirmed if you see a qualitative positive with a more sensitive 15 ng/mL cutoff quantitative assessment.
Even though SAMHSA sets standards regulating urine tests, the wide variability in marijuana use and individual differences in genetics and biology stymie efforts to develop certain time windows for detection.
You might be wondering if secondhand smoke will cause you to fail a drug test.
Say you’re at a party talking with someone who is smoking a joint. During your conversation, you inhaled quite a bit of the secondhand smoke, forgetting that you have a drug test in a couple of days. You don’t want to get fired. But, before you go crazy detoxing your body to flush the THC out, there’s good news.
According to a 2004 paper, your risk of testing positive on a drug test for passive marijuana smoke inhalation is limited to around a 30-minute time period following exposure. So, unless you’ve been around a joint a half hour before your drug test, you should be okay.
Medical Marijuana Patient Drug Testing
If you’re a medical marijuana patient, can you have THC in a drug test?
With CBD oil growing in popularity in the United States and cannabis for medical use being legal in many states, there’s a lot of confusion regarding medical pot and the workplace. And, both employers and employees are still unsure of where to find solid guidance. It’s not surprising that as marijuana becomes legalized in more states, there’s growing confusion about the dos and don’ts of having a job and being a medical cannabis patient.
Particularly when you not only need to take federal laws around cannabis into consideration but also the fact every state will have its own outlook on medical marijuana and the workplace and each employer is different.
It’s every employer’s responsibility to ensure their workplace is safe for everyone, which is the primary motivator in conducting workplace drug tests. This is mainly due to the immense belief that marijuana use leads to substantial risk while on the job, whether it’s due to impaired abilities or lack of concentration.
Although many states have legalized weed for medical use, federal law still classifies cannabis as an illegal substance. Basically, this means no matter where your state stands on medical pot, if your employer is under federal control, having a medical marijuana card means nothing.
Most state’s employers can fire you legally if your drug test comes back positive, even if your state has legalized medical cannabis. But some states explicitly state an employer can’t fire a medical weed patient for using the herb off premises.
If you’ve failed a drug test recently and aren’t sure what your next step should be, check the laws of your state. It can’t be stressed enough how important this is. If you’ve just failed a drug test because of medical cannabis, here are some steps you can take:
Take heart — you won’t face criminal charges if you fail a drug test for medical marijuana if you reside in a state that legalizes the herb.
Contest your employer’s decision to let you go if you failed the workplace drug test. In most states, your employer must give you a copy of your test results, and you can challenge the results with either an explanation or retest. Your employer might even look the other way, depending on how valued you are in your workplace.
Remember, some state laws offer workplace protections. This means if you reside in a state with employment protections, your employer can’t dismiss you for using medical cannabis outside of work.
Learn More Through MarijuanaDoctors.com Resources
Even the most knowledgeable medical pot patient can easily become confused by the laws around drug testing. The best thing you can do is educate yourself on your state laws regarding drug testing. Knowing what you can and can’t do legally will help you pass a drug test successfully.