How Long Does Medical Cannabis Stay in Your System?

Alternaleaf Team
Written by
Alternaleaf Team
May 29, 2023
Last updated:
Dec 15, 2023

Every year tens of thousands of Australians receive medical cannabis prescriptions. If you’re one of them, it’s important to understand how your body processes medical cannabis. With this knowledge you’ll feel confident in your treatment plan and know how to avoid any issues with impaired driving laws or your workplace.

How Do Our Bodies Process Medical Cannabis?

How your body processes medical cannabis depends on how you consume it. There are two main ways to consume medical cannabis: inhalation and ingestion. Inhalation refers to smoking or vaping the cannabis flower, while ingestion means consuming edibles, capsules, oils or tinctures.

When you vape medical cannabis, the active cannabinoids – THC and CBD – are vaporised and enter the lungs. The cannabinoids then pass directly into your bloodstream, where the THC will quickly take effect.

Meanwhile, medical cannabis products that you ingest will first be broken down (metabolised) in the liver before passing into the bloodstream. As a result, you normally won’t feel the effects until 30-60 minutes after consumption.

From here, inhalation and ingestion share a common process. The THC in your bloodstream enters your liver and is metabolised into the compound responsible for medical cannabis’s psychoactive effects, 11-OH-THC.

This is then converted again into an inactive compound called THC-COOH. THC-COOH is stored in your fatty tissue and released gradually into the bloodstream over days or weeks before eventually being excreted as waste.

What Factors Affect How Long THC Stays In Your System?

Everyone’s body is different, so unfortunately there’s no simple answer.

How long THC stays in your system depends on many factors. These include the quantity consumed, the percentage of THC in the medication, frequency of consumption and your metabolism & body composition. Also, the more THC your medical cannabis has, the longer it remains in your system.

How quickly THC levels peak in your body depends on how you consume it. If you ingest THC, the peak concentration will arrive around 1.5 hours after consuming it. If you inhale using cannabis flower or a vape cart, the peak arrives much quicker, with delta-9-THC peaking in the first 3-10 minutes and and 11-OH-THC concentration reaching its highest level after 15 minutes. However, this study suggests that THC is still detectable in saliva for around 12 hours in occasional users, and as long as 30 hours for more frequent users.

If you use medical cannabis frequently, THC may be detectable in your body for longer than casual users. This is because THC metabolites like THC-COOH build up in stored fats and organs over time as your body doesn’t have time to fully process them. THC-COOH has been detected in the system of heavy users more than 25 days post use.

Most tests for medical cannabis check for THC or THC metabolites, so its important to ensure that you're using a 100% pure CBD product with all traces of THC removed (this is known as an isolate CBD oil). Many products claiming to be "pure" still contain trace amounts of THC, which can build up over time and trigger a positive test.

How Long Can THC Be Detected In Your System?

The length of time it takes for THC to no longer be detectable depends on what test is being used and your own frequency and type of use.

  • Saliva: THC will be detected in saliva for at least 4-6 hours after inhaling cannabis, but may be present up to 12 hours later for occasional users and 3 days for heavy users. However these timings are highly variable and dependent on your saliva flow rate and composition, how recently you ate and frequency of use.
  • Blood: THC is usually still detectable in the blood of occasional users 7 days after use, while for heavy users it can be up to 30 days.
  • Urine: Urine tests can usually detect THC up to 24 days after use. THC-COOH (the metabolite usually tested for in workplace drug tests) may be detected for up to three-months in heavy users.
  • Hair: hair follicle tests can potentially detect THC use from years ago, depending on the rate at which your hair grows (although the THC will not appear in your hair follicles until a week or so after use).  

It's important to remember that these are not exact measurements and the safest option if you're worried about being tested is always to not consume THC.

Will You Be Drug Tested As A Legal Medical Cannabis Patient?

Legislation in Australia has yet to catch up with the widespread use of medical cannabis. It’s important to know when you might encounter a drug test as a medical cannabis user. Understanding when and where you may be drug tested will help you use medical marijuana safely.

Roadside Testing for Medical Cannabis

Any police officer in Australia can pull you over and request a roadside drug test. This is the most common type of test you’ll encounter – it’s usually a saliva test designed to detect THC.

In Australia it’s illegal to have any THC in your body while driving (with the notable exception of Tasmania). Australia’s police officers also don’t need further proof of intoxication to request a drug test, unlike many other countries. If you test positive, another test will follow to confirm the initial reading.  

If you use medical cannabis, it’s important to know that roadside drug tests aren’t designed to detect intoxication. Rather, they detect any amount of THC in your body, meaning you could test positive even while not in any way impaired.

Workplace Testing for Medical Cannabis

You may also be asked to complete a medical cannabis test at work. This is most common in the defence force and industries where safety is critical, like mining, construction, healthcare and education.

Workplaces like these use saliva, urine and occasionally hair follicle tests. These tests may detect medical cannabis used several days or weeks earlier. Knowing your workplace’s policy on medical cannabis and prescription medicine will help you stay safe.

Is There a Way to Metabolise Medical Cannabis Faster?

The short answer is no, but exercising, eating healthy and staying hydrated makes a small difference. But at the end of the day, your body needs time to break down the THC in your system.

Certain cannabis detox kits and remedies suggest diluting your urine by drinking large amounts of water and then masking the dilution with herbal supplements such as vitamin B12 and creatine. These kits don’t work and quickly drinking large amounts of water can be dangerous.

Make Informed Choices About Your Medical Cannabis Prescription

Since there’s no straightforward answer to how long medical cannabis stays in your system, it’s important to speak to your doctor if you think you might face cannabis testing in the future – THC products may not be the right fit for you.

If in doubt, play it safe. Remember that THC can remain in your system for days, weeks or even months after you use cannabis. And while medical cannabis is becoming more broadly accepted, users must still comply with driving laws and the requirements of their workplace.

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