TOOL · THC DETECTION

How long is THC detectable?

Pick frequency and body-fat range — we show the estimated detection window for urine, blood, saliva and hair in Switzerland.

Key facts
Urine, occasional
1–3 days
Urine, daily
up to 30 days
Blood (THC)
6–24h
Swiss driving limit
1.5µg/L
Origin
Indoor, Swiss producers
Members
—
across Switzerland
Last editorial review

Estimated detection window

Urine
3–7 days
Blood
1–7 days
Saliva
1–24 hours (up to 72 h in heavy users)
Hair
up to 90 days
Switzerland's blood-THC limit for driving is 1.5 µg/L — even one joint can exceed it for 4–8 hours.
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Estimate — individual values vary widely with metabolism, hydration and test method. A positive test is not the same as impaired driving.

Methodology: how this tool calculates

The detection calculator estimates how long THC metabolites stay detectable. It combines consumption frequency, sample matrix (urine, blood, saliva, hair) and body factors rather than a single half-life.

The calculation step by step

  1. 1. Pick the matrix

    Each sample type has its own window: saliva hours to 1–2 days, blood 1–3 days, urine days to weeks, hair months.

  2. 2. Weight consumption frequency

    THC is fat-soluble and accumulates. Single use, occasional, regular and daily use each get a distinct base window.

  3. 3. Correct for body factors

    Body fat, metabolism and hydration shift the window by days, which is why the tool returns a range rather than a point value.

  4. 4. Output the range

    The result spans from "negative at the earliest" to "still positive in the worst case".

Worked example

  • Regular use (3–4×/week), urine matrix, average body fat.
  • Base window for regular use: 7–21 days.
  • Higher body fat correction: +2 to +5 days.
  • Result: roughly 9–26 days before a urine test should turn negative.

Limits of the method

  • Cut-off values differ per lab and assay (e.g. 20 vs 50 ng/ml).
  • The tool is not legal advice and no evidence towards authorities.
  • Swiss road traffic law applies zero tolerance for THC — fitness to drive is not the same as detectability.

Data basis

  • Toxicological detection windows from forensic literature.
  • Swiss traffic law: Road Traffic Act and the ordinance on limits of quantification.

Frequently asked questions about the tool

Can elimination be sped up?

Not substantially. Drinking water dilutes the sample but does not remove metabolites stored in fat tissue.

Why does hair stay positive so long?

Metabolites are embedded into growing hair; roughly one month is captured per centimetre.

Does this apply to CBD products?

CBD itself is not scored as THC, but legal CBD flower contains up to 1.0% residual THC, so positive tests remain possible with frequent use.

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