How long does CBD stay in your blood and saliva?
After a single dose of mouth spray, blood CBD falls by half within 1.4 to 10.9 hours; with repeated oral doses the half-life stretches to 2 to 5 days, because CBD is stored in fat. Clearing 97% takes about five half-lives. In saliva, CBD peaks half an hour after an oil and then falls fast. Roadside tests do not look for it; a positive result comes from the THC in a full-spectrum product.
Key takeaways
- Measured CBD half-lives run from 1.4 to 10.9 h (single spray dose) through 31 h (smoked) to 2 to 5 days (repeated oral use).
- Taken twice a day, the medicine Epidyolex shows a half-life of 56 to 61 hours.
- French police saliva kits react to THC at 15 ng/ml, and the confirmation analysis detects down to 1 ng/ml.
- An oil supplying 2.8 or 3.7 mg of THC made the saliva of 8 participants out of 10 test positive in a 2026 trial.
- French driving law has no THC threshold, and a legal product is no defence.
Half-life: what the studies measure
Half-life is the time a substance's blood concentration takes to drop by half. For CBD it depends heavily on how it is taken and how often. Pooling 24 human studies, a 2018 systematic review reports these values:
| Route and use | CBD half-life in blood | Source |
|---|---|---|
| Mouth spray, single dose | 1.4 to 10.9 h | Millar et al., 2018 |
| Intravenous | 24 h | Millar et al., 2018 |
| Smoked | 31 h | Millar et al., 2018 |
| Oral, repeated daily doses | 2 to 5 days | Millar et al., 2018 |
| Epidyolex, two doses a day for 7 days | 56 to 61 h | EMA, summary of product characteristics |
Blood levels peak within 4 hours of an oral or mouth dose. Single and repeated use differ because CBD is lipophilic: it dissolves in fat, spreads into the tissues and leaves them slowly. Regular use fills this reservoir further, so elimination takes longer.
Food changes the picture too. The Epidyolex summary of product characteristics reports that a high-fat meal multiplies the peak blood level by 5 and total exposure by 4 compared with an empty stomach. One dose can thus deliver different amounts of CBD to the blood depending on when you take it.
How long it takes to clear
One half-life leaves 50%, two leave 25%, and five leave about 3%. Five half-lives are therefore treated as near-complete elimination. Applied to the published values, this gives:
- After a single dose of mouth spray, from 7 hours to a little over 2 days.
- For smoked CBD, about six and a half days, on the only published value.
- With daily oral use, 10 to 25 days after the last dose.
- For Epidyolex at medical doses, about 12 days.
These durations come from small studies and give orders of magnitude only. They vary between people with body fat, liver function, dose and product. Since no roadside test looks for CBD, they tell you nothing about a drug test.
In saliva: a quick peak, then a drop
Saliva data are recent. For a US trial published in 2026 in the Journal of Analytical Toxicology, 60 volunteers took an oil containing 100 mg of CBD twice a day for 14 days. Salivary CBD reached a median peak of 2,198 ng/ml half an hour after the dose and then fell fast. The authors attribute most of this peak to oil left in the mouth, with CBD absorbed into the blood accounting for less of it.
The trial also addresses the question that matters, THC. Each group's oil contained 0, 0.5, 1, 2, 2.8 or 3.7 mg of THC per dose. At 0.5 mg, 1 participant out of 10 tested positive for THC between 1.5 and 6 hours after a single dose; at 2.8 or 3.7 mg, 8 out of 10 did. The cutoff was 2 ng/ml, the level used by workplace saliva tests in the United States.
In French terms, an oil at the legal ceiling of 0.30% THC holds close to 3 mg per millilitre. A millilitre, roughly twenty drops, thus supplies about as much THC as the 2.8 mg group received, in which 8 participants out of 10 tested positive. The French thresholds are different: under the order of 13 December 2016, 15 ng/ml for the roadside kit and 1 ng/ml for the confirmation analysis.
Blood and urine: what the analyses look for
The body does not appear to convert pure CBD into THC. In a 2022 study, 18 adults took 100 mg of CBD, swallowed or vaporised, and their urine was followed for 58 hours. Pure CBD left no trace of Δ⁸- or Δ⁹-THC. A CBD-rich cannabis that supplied 3.7 mg of THC was another matter: 3 participants out of 18 then gave urine samples positive for the THC metabolite.
For cannabis, the orders of magnitude for THC come from the detection-time table from Drogues Info Service, the French public drug information service:
| Sample | Occasional use | Regular or heavy use |
|---|---|---|
| Saliva | 6 to 8 h | up to 24 h, up to 8 days with heavy daily use |
| Blood | THC 2 to 8 h, metabolite up to 72 h | more than a month with heavy use |
| Urine | 3 to 5 days | 30 to 70 days |
A dose of a CBD product usually carries less THC than a joint, yet no official source gives a detection time for CBD products. For how a roadside check works, see the CBD and saliva test guide; hair is covered in the hair test.
At the wheel: the rule that applies
Article L235-1 of the French Highway Code punishes driving after drug use with 3 years in prison and a €9,000 fine, and sets no THC threshold. The Court of Cassation ruled on 21 June 2023 that the permission to sell hemp products under 0.30% THC has no bearing on this offence. No waiting period guarantees a negative test.
Drivers can lower the risk in three ways:
- Pick an isolate over a full-spectrum product. CBD isolate: what 99% means explains what a "99%" guarantees.
- Read the Δ⁹-THC line on the certificate of analysis: there, "ND" (not detected) does not mean the same as "0.2%". Our guide to reading a certificate of analysis covers each line, and the laboratory page describes the measurement methods.
- Stay off the road after any product containing THC: flower, resin or full-spectrum oil.
Frequently asked questions
In the 2026 trial, salivary CBD peaked half an hour after an oil and then fell fast, mostly because of oil left in the mouth. This has little practical weight, since the police saliva kit detects THC.
The half-life is 1.4 to 10.9 hours after a single spray dose and 2 to 5 days with daily oral use. Near-complete elimination takes five half-lives: a few hours to about two days after a one-off dose, and up to 10 to 25 days after regular use.
A laboratory can measure it, but no roadside test or legal threshold is aimed at CBD. Drug tests search for THC and its metabolite, so a positive result after CBD means the product contained THC.
No official waiting time exists. An isolate with no THC detected leaves the test nothing to find. After a full-spectrum product, THC may stay detectable in saliva for several hours, longer with daily use, so the safest choice is not to drive.
Written by the Phytogrammes team
Each journal article draws on cited primary sources: ANSM, EFSA, EUR-Lex and peer-reviewed publications. Product profiles are distinguished from documented laboratory results. Our approach.
Article published on . CBD is not a medicine.