How long does medicinal cannabis stay in your system?

How long will medicinal cannabis stay in my system?

While there is no definitive answer to the question of how long medicinal cannabis (aka weed or marijuana), including medicinal cannabis, can stay in your system, studies can give us a good idea of how long cannabis may be detected in various drug tests, such as saliva, blood, urine, and hair tests. Generally, higher doses and more frequent cannabis use will lead to longer detection times. Depending on the type of test taken, cannabis may be detected in your system for up to 90 days or 3 months.¹

For cannabis to leave your system, your body first needs to convert it into less active or inactive metabolites through the process known as metabolism, which we’ll explore below.

Cannabis metabolism process

Metabolism is the body’s process of breaking down or transforming almost all of the materials that enter it, from food and drink to drugs and alternative medicines - like medicinal cannabis. The rate at which your body metabolises the cannabinoids and other compounds within your cannabis will determine how long it stays in your system.

In Australia, it is illegal to drive with any amount of THC in your system, and THC is the only cannabinoid tested for in drug tests. This is because THC is an intoxicating, psychoactive cannabinoid which can affect cognitive and motor skills that are needed for safe driving – including attention, judgement, vision, coordination and memory – at certain doses.

Studies have shown that moderate amounts of THC produce mild driving impairment lasting up to four hours. In comparison, 1500mg of the cannabinoid CBD (the highest daily medicinal dose) has ‘no impact on people’s driving or cognitive abilities’² and so is not tested for in drug tests. Learn more about medicinal cannabis and driving in Australia here.

Let’s briefly look at the metabolism process for THC, the psychoactive cannabinoid detected in cannabis drug tests:

THC metabolism process

Step 1: The cannabis plant – which contains the cannabinoid THCa – is heated in a vaporiser, or is heated in the process of being extracted into another format for oral, sublingual or other consumption methods (such as an oil).

Step 2: As the THCa in the cannabis plant heats up, it converts to THC.

Step 3: When the THC is inhaled as a vapour or delivered sublingually (under the tongue), it travels through the body via the bloodstream before reaching the liver. 

When THC is ingested / eaten, it travels to the liver via the digestive system before being taken up by fat tissue in the body and slowly released back into the bloodstream.

Step 4: THC binds to cannabinoid receptors in the body to produce varying therapeutic and other effects.

Step 5: In the liver, THC is metabolised a number of times by CYP2C and CYP3A enzymes. It is first converted into the THC metabolite 11-OH-THC (which produces further psychoactive effects) and then into 11-COOH-THC (which is not psychoactive).

Step 6: More than 65% of THC exits the body via the stool and approximately 20% is excreted in urine. Most of the THC is excreted within 5 days as hydroxylated and carboxylated metabolites, but some can remain stored in the fat deposits in the body and in hair follicles.³

Factors involved in the metabolism of cannabis

The amount of time it takes the body to metabolise medicinal cannabis and ultimately how long it will stay in your system will vary from individual to individual depending on many factors, including:

• How much medical cannabis you consume: Higher doses of cannabis generally take your body longer to metabolise, and will lead to longer detection times on drug tests.⁴
• How often you consume medical cannabis: More frequent users will generally take longer to metabolise cannabis than infrequent users, as cannabinoids have stored in the body over time.
• The potency of your medical cannabis: Different cannabis treatments will have different THC levels. How much THC is in your medication will affect how long it takes for your body to metabolise. Medications with high doses of THC are likely to stay in your system for longer.
• Your body mass index (BMI) or body fat percentage: THC is extremely fat soluble and can be stored in your body fat for an extended period. The more body fat you have, the more potential there is for THC to be stored in your system.
• How much exercise you do: Physical exercise can help burn fat and speed up metabolism, reducing the amount of fat cells for THC to be stored in over time. However, in regular cannabis users who have accumulated stores of THC in body fat, exercise may actually increase the amount of THC in your blood plasma by releasing dormant THC from fat stores.⁵‍
• Your individual metabolism: Metabolic function varies from person to person, with other factors like age, sex, health, liver function and more also playing a part.

Can you speed up the cannabis metabolism process?

The most effective way to ensure you do not have any THC in your system is to abstain from THC for an extended period of time. How long you choose to abstain from THC may depend on any of the cannabis metabolism factors mentioned above, or on your driving status, work status or type of drug test you may need to take.

Maintaining good health during your abstinence period by drinking the recommended amount of water each day, eating a healthy diet and exercising may help your body metabolise and expel THC stores more effectively. But, there is no evidence to suggest that doing excessive amounts of any of these things will speed up the cannabis metabolism process.

Beware of any ‘cannabis detox’ products or methods that promise to magically flush out THC from your system in a short period of time. There is no evidence-backed supplement, cleanse, juice, tea, drink or product that can rapidly eliminate THC stores in the body. If you are a medicinal cannabis patient who regularly uses THC, your best bet is to abstain from THC and take a cannabis break to support the healthy functioning of your body, metabolism and liver and organs through adequate hydration and a healthy diet and lifestyle.

How long will a drug test detect cannabis in your system? 

There are a number of different tests used to detect cannabis in the body. These tests measure the cannabinoid THC and THC metabolites which can remain in your system long after the effects of THC have worn off. 

How long THC stays in your system depends on the factors above while the likelihood of THC showing up on a drug test will depend on the testing method used. Common tests for THC include:

Urine test 

A urinalysis (or urine test) is one of the most commonly used tests for detecting THC in Australia. Urine testing tests for the metabolite 11-COOH-THC, which can be detectable in urine for as long as 30 days or more, depending on the individual.

A 2017 review⁶ of urine tests found that THC was detectable in urine for varying durations after last use, depending on the following frequencies of cannabis consumption:

• Occasional users (up to three times a week): 3 days
• Moderate users (four times a week): 5 to 7 days
• Chronic users (daily): 10 to 15 days
• Chronic heavy users (multiple times a day): more than 30 days

Saliva test 

Saliva tests use saliva samples to detect THC. They are another common type of test performed in Australia, particularly in random roadside testing.

Generally, saliva tests can detect THC for about 12 hours after use in people who use cannabis infrequently. But for those who frequently use cannabis, such as medicinal cannabis patients who use cannabis to help treat chronic conditions, THC can usually be detected for around 30 hours after use.⁷

Hair follicle test 

The hair test can detect cannabis for the longest duration after last cannabis use. Research shows that THC in hair can produce a positive test after 3 months (or 90 days) of last drug intake.⁸

Blood test 

Blood tests typically detect recent cannabis use, or use that has occurred within the last 2 to 12 hours.⁴ In heavy, daily cannabis users, THC can be detected in the blood for up to 7 days.⁹

THC which has been dormant in fat stores of frequent cannabis users may also be released into blood plasma following exercise, which may be detectable on blood tests.⁵

Cannabis detection in roadside drug testing

It is currently illegal to drive with any amount of the cannabinoid THC in your system in all states in Australia (except Tasmania), even if you are a medicinal cannabis patient with a valid prescription. If you choose to take THC or do not wait long enough for the THC to leave your system before you drive and you test positive for THC in a mouth swab/saliva test, you can lose your licence.

Random roadside drug testing uses saliva tests to detect THC. However, these tests have limitations. One study conducted by the Lambert Initiative for Cannabinoid Therapeutics in Australia found that roadside drug tests often failed to detect THC, while also producing false positives for THC presence up to 10% of the time.¹⁰

Because it is so difficult to know the exact detection windows after consuming THC, if you are a medicinal cannabis patient who has to drive frequently, you may want to consider a CBD treatment rather than a THC one under the current driving laws in Australia. Ensure you are open and honest with your prescribing doctor about your driving status and current situation so they can provide you with a treatment plan that works best for you.

FAQ: 

Does CBD oil show up in an Australian drug test? 

Routine drug tests in Australia, including roadside saliva tests and workplace cannabis drug testing, do not screen for the cannabinoid CBD. This is because CBD is a non-intoxicating compound that does not impair driving or other cognitive abilities.¹¹

CBD oil or any other CBD medication that does not contain the cannabinoid THC will not show up on roadside or workplace drug tests, as these are testing for THC metabolites from the psychoactive cannabinoid THC (which can be impairing) and other drugs or illicit substances. 

If you're considering using medicinal cannabis in Sydney, Melbourne, Perth, or other areas and are curious about its implications, speaking to a healthcare professional who specialises in medicinal cannabis is a great first step.

Do at-home drug tests work?

At-home drug tests generally use either urine or saliva to detect cannabis. Like laboratory tests, at-home drug testing kits test for the presence of THC metabolites, and will provide either a positive or negative result.

No test of this type is 100% accurate, and a number of factors can influence results, including:

• the way you did the test
• the timeframe you took the test in
• the way you stored the test or sample
• what you ate or drank before taking the test
• any prescription, over-the-counter or other drug use prior to the test

While at-home tests may provide a useful indication for the presence of THC, laboratory tests are the most reliable way to confirm if THC is in your system.

Can secondhand smoke make you fail a drug test? 

Secondhand smoke is unlikely to make you fail a drug test or produce a false positive under normal circumstances.

One 2015 study¹² has shown that extreme cannabis smoke exposure can produce positive urine tests at commonly utilised cutoff concentrations. However, these positive tests are likely to be quite rare, limited to the hours immediately post-exposure, and occurring only under environmental circumstances where exposure is obvious. 

An earlier 2005 study¹³ which placed cannabis smokers and non-smokers together in a vehicle showed that when collected properly and with a waiting period before collection, the risk of a positive result from secondhand smoke exposure was virtually eliminated in oral fluid testing.