Learn Cannabis: What is the Half-Life of THC?

The brain and THC, Half-life of THC iStock / Shidlovski

The half-life of THC, like other drugs, refers to how long it takes for half the dose to be eliminated from your system. Pharmacologically speaking, when a drug reaches its half-life, only half the original concentration will remain in your body. Half-life of THC is not directly correlated to feeling high. Some drugs have very long half-lives, but, when ingested, the felt effects only last for a short amount of time. Valium, the drug commonly used for anxiety or as a sleep aid, possesses a very long half-life, somewhere in the ballpark of 30 to 40 hours (or higher in some people). But popping a valium won’t leave you relaxed for an entire day!

The Half-Life of THC

THC is the fun uncle of the cannabis plant, the cannabinoid that makes weed, weed. Some people want to know the half-life because they’re curious about how long their high will last; others have heard rumors around the water cooler of an impending drug test and are curious if they should start updating their resume. How quickly THC gets you high is largely dependent on how you consume it: if you smoke it, peak plasma concentration occurs around eight minutes later. If you eat it, these concentrations happen around one to two hours later.

As for half-life of THC, this is largely dictated by how often you smoke marijuana: for the occasional, social smoker, the half-life is around 1.3 days. For those who smoke regularly, it’s between 5 days and 13 days. This is average, of course, and the true half-life for you can be shorter or longer. Keep in mind that half-life doesn’t mean the entire drug is eliminated; only half. So THC may have a half-life of 1.3 days in a no-frequent smoker, but they wouldn’t be completely THC free for several days after that. At the 2.6 day mark, the level would be half of the 1.3 day mark and so on and so on.

Couple sharing a joint

iStock / monkeybusinessimages


This doesn’t guarantee THC is detectable until it’s 100 percent gone; the levels may be below the cutoff parameters of drug tests.  If drug testing is of a concern (and it likely is if you googled an article on the half-life of THC), the rule of thumb is to abstain for a week or so no matter what type of user you are. For light users, this should clear it enough for you to pass a drug test.

If you consume marijuana with frequency, it can take around three weeks to clear from your system, especially if the test used has a strict threshold. If you consume it on a daily basis, it can take a month or more for your body to reach an adequate level of clearance.

More than simply half-life goes into this: body fat plays a role too. In general, thinner people store less THC and thus pass drug tests easier than heavier people who smoke the same amount.

What Influences Half-Life?

Some drugs have longer half-lives than others. Valium, as mentioned above, is among the drugs with a lengthier than is typical half-life. For those who take it, this can be beneficial: it decreases withdrawal symptoms.

Your body determines some of this too. Liver and kidney function can help dictate how quickly a drug is eliminated from your system. If a drug is eliminated through the kidneys, for instance, someone with kidney problems who has compromised urine output would eliminate the drug at a slower rate than someone with a normally functioning renal system.

Your genes can influence this as well. The CYP2D6 enzyme (which is responsible for the elimination of many drugs) is expressed differently in different people. As a result, some people are poor metabolizers (which means they eliminate the drug slower than usual), some are efficient metabolizers (which means they eliminate the drug in what is considered the “normal” amount of time), and some are ultra-rapid metabolizers (which means they eliminate the drugs quicker than usual).

Drugs and dosages given to poor or ultra-rapid metabolizers may be altered by prescribing physicians. Anti-depressants, for instance, aren’t often effective in ultra-rapid metabolizers because their bodies chew up the drugs before they can do their jobs. Tramadol and codeine, because they contain metabolites that are converted at a quicker than usual pace, are more effective in ultra-rapid metabolizers. Lower than normal doses are often recommended in these cases.

Learn Cannabis: What is the Half-Life of THC? was last modified: by
Jenn Keeler
About Jenn Keeler
Jenn Keeler is a freelance writer and illustrator specializing in humorous lifestyle articles. She is one of the few people on earth actually using an English degree. Her heart belongs to the Denver Broncos and her husband. In that order.