THC and Drug Tests: Detection, Cutoffs, and What Affects Them

What a THC test actually detects

Federal (DOT): A urine test does not look for THC. It looks for THCA, one of the compounds your body produces while processing THC — the regulation names marijuana metabolites specifically Source 1DOT ODAPC49 CFR §40.85 — What are the drug test cutoff concentrations? — checked 17 Aug 2026Source 2eCFR49 CFR §40.85 (current text) — checked 17 Aug 2026.

Federal (HHS): An oral fluid test does the opposite: it measures delta-9 THC itself, the parent compound Source 3HHSMandatory Guidelines for Federal Workplace Drug Testing Programs — Authorized Testing Panels — checked 17 Aug 2026.

This distinction explains a lot of apparent contradictions. The two specimens are measuring different molecules, present in different amounts, on different timescales. A number from one tells you nothing about the other.

The cutoffs that apply

Federal (DOT): For DOT testing, marijuana metabolites screen at 50 ng/mL and confirm at 15 ng/mL, and those figures have not changed since May 2023 Source 1DOT ODAPC49 CFR §40.85 — What are the drug test cutoff concentrations? — checked 17 Aug 2026Source 2eCFR49 CFR §40.85 (current text) — checked 17 Aug 2026.

Employer policy: An employer testing outside a federal programme can set its own level, and at-home tests come in several. This is why the same person can be negative on one test and positive on another on the same day — the tests are drawing the line in different places Source 5FDADrugs of Abuse Home Use Test — checked 17 Aug 2026.

Why nobody can give you an exact detection window

This is the question most people actually came for, and the honest answer is that it depends on you. Frequency and quantity of use dominate, and body composition, metabolism and hydration all contribute. A one-time user and a daily user can differ by weeks, not hours.

Official sources set cutoff concentrations, not detection windows — there is no regulation stating how long THC remains detectable, because it is not a fixed property. Any article giving you a single confident number is either describing an average as if it were a rule, or making it up.

What can be done responsibly is an estimate with its reasoning shown, based on your own pattern of use. That is what our calculator does, and it is framed as an estimate rather than a guarantee, because that is what it is.

CBD products and what they can do

A CBD product can contain enough THC to produce a positive result. Labelling is not always reliable, full-spectrum products contain THC by design, and a test looking for THCA does not care what the bottle said.

There is no way to use a CBD product and be certain it will not affect a test result. If you are subject to testing in a safety-sensitive role, that is a risk worth understanding before rather than after.

State cannabis law does not change the test

State law: Legal cannabis in your state changes what your state permits. It does not change what a test measures, and it does not change the federal position.

Federal (DOT): For a DOT-regulated role in particular, no state law alters what a positive marijuana result means Source 6eCFR49 CFR Part 40 — Procedures for Transportation Workplace Drug and Alcohol Testing Programs — checked 17 Aug 2026. Some states do restrict what employers may do about cannabis results, generally with safety-sensitive roles excluded — which is state employment law, not testing science.