Blog
How Long Does Cannabis Stay in Your System? UK Guide
If you have a workplace screening or another drug test coming up, one question comes up quickly: how long does cannabis stay in your system? The honest answer is that it depends. The type of test matters, and so does how often someone uses cannabis and a handful of personal factors.
This guide pulls together detection windows published by several UK-facing health and information sources. It explains why the figures differ and what to keep in mind when you read them. It is general information, not medical or legal advice, and none of these numbers is a guarantee.
Why there is no single answer
Drug tests usually look for THC, the main psychoactive compound in cannabis, or for the metabolites it leaves behind. Different tests look in different places, such as urine, saliva, blood, hair or sweat. Each has its own window.
Priory Group notes that its figures can vary depending on the amount consumed and how often the person generally takes the drug. Medical News Today makes a similar point, adding that the type and sensitivity of the test affect the result. So any number you read is best treated as a rough range.
Detection windows by test type
The ranges below come from Priory Group, Releaf and Medical News Today. Where sources differ slightly, both figures are shown.
| Test type | Reported detection window |
|---|---|
| Blood | About 24 hours (Releaf) to 24-48 hours (Priory Group) |
| Saliva | 24-72 hours |
| Urine | 1 to 30 days, depending on the source and the pattern of use |
| Hair follicle | Up to 90 days |
| Sweat | 7-14 days (Medical News Today) |
Blood and saliva: the shorter windows
Blood and saliva tests cover the shortest periods. Priory Group gives 24-48 hours for blood and 24-72 hours for saliva. Releaf gives a similar saliva range and puts blood at around 24 hours.
Urine: the most common method
Releaf describes urine testing as the most common drug screening method. It says THC metabolites can be detected from 3 days after a single dose. For patients who take medical cannabis regularly, it says this can extend to 30 days.
Other sources give wider ranges. Priory Group lists 3-30 days, and Medical News Today lists 1-30 days. Substance Misuse Resources, writing about UK workplace testing, says cannabis can be detected in urine for 1-3 days after occasional use and for 28 or more days in daily users.
Hair and sweat: longer lookbacks
Hair follicle tests have the longest reported window, up to about 90 days according to Priory Group, Releaf and Medical News Today. Medical News Today also lists sweat testing at 7-14 days, though this is less commonly discussed than urine or hair.
How frequency of use changes the picture
Frequency is one of the biggest factors. Medical News Today suggests tests may detect cannabis for:
- about 3 days after first-time use;
- 5-7 days for someone who smokes it 3-4 times a week;
- 30 days or longer for people who smoke it once a day or more.
These match the wider pattern in the urine figures above. Occasional use sits at the short end of the range, and daily use sits at the long end.
Other factors that can affect detection time
Frequency is not the only variable. Releaf says the detection window varies with:
- body fat;
- speed of metabolism;
- dose size;
- how often cannabis is used;
- THC potency;
- how the cannabis is taken.
Medical News Today also lists body composition among the influences. Two people who use the same amount can therefore end up with different results. This is why a published range is an estimate rather than a countdown timer.
Practical points to keep in mind
Treat ranges as estimates
The sources above give ranges, not certainties. If a test matters for your job or another situation, work from the longer end of the range rather than the shorter one.
Know which test you are facing
If you are asked to take a test, ask what type it is. The difference between a saliva swab and a hair test is large in terms of how far back they can look.
Be wary of quick-fix claims
None of the sources used for this article offers a reliable way to speed up how quickly cannabis leaves your system, so we will not suggest one. Be sceptical of products or websites that promise to “cleanse” you before a test. Our guide to spotting fake cannabis websites is a useful read if you are unsure who to trust online.
Tell the right people if you use medical cannabis
Releaf notes that regular medical cannabis use can extend urine detection to 30 days. If you take a prescribed treatment and face a test, speak to your prescriber or the person organising the test. Our overview of medical cannabis in the UK explains more about how prescribed products and vaporisers fit into the picture.
Check labels on CBD products
If you use CBD products, read the label carefully and understand what is in them. Our article on CBD oil, THC and labelling in the UK covers what to look for. The sources used here do not say how CBD products relate to test results, so if that worries you, ask the organisation running the test.
What this guide does not cover
This article does not cover drug-driving rules or any legal limits for THC. We have not verified those against an official UK government source, so we have left them out. If you need to know where you stand legally, check current official guidance on gov.uk.
Conclusion
So, how long does cannabis stay in your system? Reported windows run from around a day for blood, through a few days for saliva, to anything from 1 to 30 days for urine. Sweat is listed at 7-14 days and hair at up to 90 days. Occasional use tends to sit at the short end of those ranges, and daily use at the long end.
Body fat, metabolism, dose, potency and method of use all play a part. That means no published figure can promise what your own result would be. Use the ranges as a guide, plan around the longer end, and ask the test provider about the method they use.
For the original figures, see the detection-time articles from Priory Group, Releaf and Medical News Today.