How Long Does Weed Stay In Your System?
Cannabis use is increasing across Australia, both recreationally and through prescribed medicinal cannabis programs. However, many companies in industries such as transportation, mining, and construction require employees to undergo drug tests for pre-employment screening, random workplace testing, or return-to-work checks. This raises the question: how long does weed stay in your system?
Understanding cannabis detection times is crucial for individuals in roles that require regular checks. Even if the effects feel long gone, cannabis can leave traces in the body that remain detectable for days or, in some cases, weeks. This can impact workplace safety requirements, employment timelines and medical clearance for certain roles.
In this guide, we break down everything you need to know about cannabis detection, test passing requirements, and what to consider if you think THC might appear on your upcoming test.
What Effect Does Cannabis Have and Why Do Workplaces Test For It?
The main psychoactive compound in cannabis is THC (tetrahydrocannabinol). It interacts with receptors in the brain and nervous system, affecting:
- Coordination and motor skills
- Reaction time
- Decision-making and judgement
- Concentration and memory
These effects can impair performance and increase the risk of accidents, particularly in high-risk industries such as transport, mining, construction and manufacturing.
Under Australian Work Health and Safety laws, employers are required to provide a safe working environment. Drug testing helps:
- Reduce workplace accidents and near-misses
- Support fitness-for-duty requirements
- Meet WHS and industry compliance standards
- Identify when an employee may need well-being support
According to the Australian Institute of Health and Welfare, cannabis is the most widely used illicit substance in Australia, with approximately 11.5% of adults reporting use in the past year. Given this, clear workplace policies and testing protocols are essential.
Can You “Pass” If You Used Weed Recently?
Drug tests do not measure how “high” someone is. They detect whether THC metabolites are present above a certain threshold.
A “pass” means:
- THC is below the cut-off level, or
- A Medical Review Officer confirms valid medicinal cannabis use (if policy allows)
Someone may feel sober yet still test positive if their body has not fully cleared the metabolites, which is why timing matters.
How Long Does Weed Stay In Your System?
Cannabis detection time varies based on:
- Frequency of use
- THC strength and dosage
- Metabolism and body fat levels
- Hydration and activity level
- Method of consumption (smoking, vaping, edibles, oils)
THC is stored in fat cells and gradually released; therefore, regular or heavy use significantly increases the detection window.
Detection Windows By Test Type
| Test Type | Detects | Rough Detection Window |
| Saliva (oral fluid) | Recent use, impairment risk | 6-24 hours (up to 72 hrs in heavy users) |
| Urine | Past use, not impairment | 2-7 days for occasional users; up to 30 days for heavy daily use |
| Blood | Current or very recent use | Up to 24-48 hours |
| Hair | Historical use | Up to 90 days |
| Instant drug tests (onsite kits) | Initial screening for recent use | Similar detection ranges to saliva/urine (positives require lab confirmation) |
Workplaces may use instant drug tests for immediate results. If an on-site test detects cannabis above the cut-off, the sample is then sent to a laboratory for confirmation. This protects employees from false positives and ensures fairness.
What Do You Do If You Think Cannabis Will Show Up On Your Test?
If you believe cannabis may still be in your system, the most important step is communication and understanding your workplace policy.
For Employees:
- Review company drug and alcohol guidelines
- If prescribed medicinal cannabis, disclose privately as required
- Ask clarifying questions if unsure about policy or testing timelines
- Avoid “detox myths” – water loading, cleanses and online “hacks” are not reliable and can raise concerns
If a result does come back “non-negative,” laboratory confirmation and review by a Medical Review Officer ensure context is applied fairly.
For Employers:
Encourage transparency and provide support, not stigma. Many organisations pair testing programs with access to Employee Assistance Programs and wellbeing support, recognising that substance use and mental health can be linked.
Keeping Employees Safe and Aware
Cannabis can stay in your system for anywhere from several hours to several weeks, depending on frequency of use, metabolism and the type of test used. Understanding these timelines and how drug testing works helps employees prepare responsibly and enables employers to run fair, safe and compliant workplaces.
If your business needs trusted workplace drug testing, guidance on policy development or pre-employment medical checks, Safework Health is here to help.
Safework Health is a trusted partner for workplace drug testing across Australia. We combine scientific accuracy with professional, non-judgmental processes to support both compliance and employee well-being.
We know drug testing can feel confronting for employees and complicated for employers. Our team makes the process straightforward, respectful and compliant. Speak with us today to ensure a safe, informed and compliant workplace.
It’s important to note that medicinal cannabis contains THC unless specifically prescribed as CBD-only. Employees using legally prescribed medicinal cannabis should discuss workplace policies and any disclosure requirements with their employer or medical practitioner.