In short
THC is stored in body fat and leaves slowly, so cannabis can be detected long after its effects wear off. After occasional use, a saliva test can stay positive for a day or more and a urine test for a few days. With daily use, urine can stay positive for weeks and blood for up to a month. A positive roadside test is an offence in most of Australia, even if you are no longer affected.
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Why cannabis lingers
The effects of cannabis are short. If it is smoked or vaped, they are felt straight away and peak within 15 to 30 minutes. If it is eaten, they start within 30 minutes to 2 hours and peak at 1 to 4 hours. Either way they can last up to 24 hours.1
Detection is a different story. THC, the chemical in cannabis that causes a high, is stored in the body's fat cells and released slowly.2 Drug tests look for THC itself or for the substance the body breaks it down into, and both can be found long after the effects have gone.3,4
That gap between feeling normal and testing negative is what catches people out.
How long can cannabis be detected?
There is no single answer. These are guides only, and individual results vary widely.
| Test | Occasional use | Regular or heavy use |
|---|---|---|
| Saliva (roadside tests) | Hours to a couple of days. Across drugs in general, saliva tests detect use for 5 to 48 hours.5 The Alcohol and Drug Foundation says roadside tests can detect THC up to 3 days after use.2 | In a Melbourne study of dependent users, saliva stayed positive for up to 78 hours after they stopped.4 |
| Urine | A few days. For a single dose of most drugs, urine detects use for 1.5 to 4 days.5 | Weeks. In a study of 60 cannabis users, the last positive urine test came at an average of 4 days in the group with the lowest starting levels and 15 days in the group with the highest.3 In people who use it frequently, it can be found for around a month.2 |
| Blood | About 1 to 2 days at low levels for most drugs.5 | In daily smokers, THC has been found in blood after a month without cannabis.6 |
| Hair | Hair has the longest detection time of any sample.5 | |
What changes the detection time?
How long a drug can be detected depends mainly on the dose and on how sensitive the test is. Other things matter too:5
- How long you have been using it. Regular use builds up a store in body fat
- How it was taken
- What is being tested: saliva, urine, blood or hair
- Which substance the test looks for
- Your own metabolism and kidney function, which differ from person to person
The cut-off level a laboratory uses changes the result as well. In one study, six urine samples tested positive at a low cut-off, and only two of them were still positive at a higher one.7
THC leaves the body at its own pace as it is released from fat. Time since last use is what matters.2
Detected is not the same as impaired
Being impaired and testing positive are two separate things.
- Impairment lasts hours. A review of 80 studies estimated that most driving-related skills recover within about 5 hours of inhaling a 20 mg dose of THC, and almost all within 7 hours. Cannabis taken by mouth may take longer to wear off.8 For oral medicinal products, the risk can last up to 8 hours.9
- Detection lasts days or weeks. Roadside tests detect the presence of THC, not impairment.2 You can test positive when you are no longer physically or mentally affected.10
Driving while impaired by cannabis roughly doubles the risk of a crash.11
Roadside drug tests and the law
Police carry out random roadside saliva tests for THC.2 In Queensland, a test takes 3 to 5 minutes. A positive result means a second test, and if that is positive too the samples go to a laboratory.12
What happens next depends on where you are:
- Queensland: there is zero tolerance. Any trace can be penalised, and your licence is suspended for 24 hours after a positive test.12
- Victoria: a positive result has to be confirmed by a laboratory before you can be charged.2 If a magistrate finds you guilty of a first offence, your licence is cancelled for at least six months.13
- New South Wales: the offence of driving with THC present has carried an immediate three-month loss of licence.14
- ACT: it is a crime to drive with any amount of cannabis in your system.10
What if it was prescribed?
In most of Australia a prescription for medicinal cannabis makes no difference. You can be charged if THC is found in your system while driving.15 There are exceptions:
- Tasmania: it is not an offence if the product was lawfully prescribed and taken.16
- Victoria: the magistrate can decide whether a person with a valid prescription loses their licence.13
- New South Wales: under a law passed in 2026, registered patients with an unrestricted licence will face no action if a laboratory finds THC below 50 nanograms per millilitre. Above that, a first or second detection in two years brings a warning, and a third brings a $704 fine and at least three months off the road. Anyone who tests positive at the roadside is still banned from driving for 24 hours, and impaired drivers are still charged. The register and the compulsory education course were expected in late 2026 or early 2027, and the scheme had not started at the time of writing.14,20
Does CBD show up on a drug test?
Drug tests look for THC, not CBD. In a study of 18 adults given 100 mg of pure CBD, there was no sign of CBD turning into THC in the body.7
The catch is that many CBD products contain some THC:
- When the same volunteers used CBD-dominant cannabis containing a small amount of THC, 3 of the 18 went on to produce urine samples containing the THC breakdown product.7
- Some prescribed products that do not list THC as an ingredient still contain traces of it.15
- In a United States analysis of 84 CBD products sold online, THC was found in 18.17
Workplace drug tests
Drug testing uses samples of urine, saliva, breath, hair or sweat, and it is used in some workplaces and in competitive sport.2 Because urine tests can stay positive for weeks in regular users, a positive result says little about when cannabis was last used.3
If you are prescribed medicinal cannabis and your job involves drug testing or safety-critical work, raise it with your prescriber before you start.
If you are stopping cannabis
Withdrawal is common. In a review of 47 studies of people with regular or dependent cannabis use, 47 per cent had withdrawal symptoms when they stopped. In general population samples the figure was 17 per cent.18 Symptoms can include:19
- Cravings
- Trouble sleeping
- Feeling depressed or anxious
- Changes in appetite
- Mood swings and restlessness
- Nausea
Symptoms are usually at their worst 1 to 4 days after quitting and may last about 3 weeks.19
When to talk to a doctor
- You are finding it hard to cut down or stop, or withdrawal is getting in the way19
- You use cannabis to manage pain, sleep or anxiety and want to look at other options
- You take prescribed medicinal cannabis and need advice about driving or work
The National Alcohol and Other Drug Hotline is free and confidential on 1800 250 015.9
See also is cannabis legal in Australia? and medicinal cannabis in Australia.
References
- Alcohol and Drug Foundation. Cannabis (THC).
- Alcohol and Drug Foundation. Roadside drug testing.
- Goodwin RS, Darwin WD, Chiang CN, et al. Urinary elimination of 11-nor-9-carboxy-delta9-tetrahydrocannnabinol in cannabis users during continuously monitored abstinence. J Anal Toxicol. 2008;32(8):562-9.
- Odell MS, Frei MY, Gerostamoulos D, et al. Residual cannabis levels in blood, urine and oral fluid following heavy cannabis use. Forensic Sci Int. 2015;249:173-80.
- Verstraete AG. Detection times of drugs of abuse in blood, urine, and oral fluid. Ther Drug Monit. 2004;26(2):200-5.
- Bergamaschi MM, Karschner EL, Goodwin RS, et al. Impact of prolonged cannabinoid excretion in chronic daily cannabis smokers' blood on per se drugged driving laws. Clin Chem. 2013;59(3):519-26.
- Sholler DJ, Spindle TR, Cone EJ, et al. Urinary Pharmacokinetic Profile of Cannabidiol (CBD), Δ9-Tetrahydrocannabinol (THC) and Their Metabolites following Oral and Vaporized CBD and Vaporized CBD-Dominant Cannabis Administration. J Anal Toxicol. 2022;46(5):494-503.
- McCartney D, Arkell TR, Irwin C, et al. Determining the magnitude and duration of acute Δ(9)-tetrahydrocannabinol (Δ(9)-THC)-induced driving and cognitive impairment: A systematic and meta-analytic review. Neurosci Biobehav Rev. 2021;126:175-193.
- healthdirect. Medicinal cannabis.
- Legal Aid ACT. Cannabis factsheet.
- Hall W. What has research over the past two decades revealed about the adverse health effects of recreational cannabis use?. Addiction. 2015;110(1):19-35.
- Queensland Government. Drugs and driving.
- Victoria Legal Aid. Drug driving.
- NSW Government. Medicinal cannabis driving reforms introduced to Parliament.
- Therapeutic Goods Administration. Medicinal cannabis: information for consumers.
- Tasmanian Department of Health. Medicinal cannabis information for patients and the general public.
- Bonn-Miller MO, Loflin MJE, Thomas BF, et al. Labeling Accuracy of Cannabidiol Extracts Sold Online. JAMA. 2017;318(17):1708-1709.
- Bahji A, Stephenson C, Tyo R, et al. Prevalence of Cannabis Withdrawal Symptoms Among People With Regular or Dependent Use of Cannabinoids: A Systematic Review and Meta-analysis. JAMA Netw Open. 2020;3(4):e202370.
- healthdirect. Cannabis (marijuana).
- NSW Government. Medicinal cannabis driving reforms pass NSW Parliament.
This guide is general information, not medical advice. It doesn’t replace a consultation with a doctor who knows your history. In an emergency, call 000.