Saliva drug tests are the primary method for roadside cannabis screening in Europe, Australia, and increasingly the US. They detect active THC in oral fluid, making them the closes
Oral fluid tests detect delta-9 THC directly — not THC-COOH like urine tests. THC enters saliva during smoking via direct mucosal absorption and from blood via the salivary glands. Lateral flow immunoassay devices provide results within 5–10 minutes roadside. Confirmatory LC/MS/MS lab analysis is used for legal proceedings. Because the test detects active THC rather than stored metabolites, it provides a narrower window that better correlates with recent use. Compare this to how urine tests detect historical metabolites rather than active THC.
In occasional users, THC in saliva typically falls below standard cutoffs within 4–8 hours of smoking. For regular users, detection may extend to 48–72 hours due to continuous THC secretion from blood. Immediately after smoking, oral THC levels can be extremely high (over 1,000 ng/mL), far exceeding cutoffs. The route of consumption matters: edibles produce lower oral fluid THC because less direct mucosal absorption occurs, but blood-borne secretion still deposits detectable amounts. Oral fluid testing cannot detect cannabis use from days ago the way urine or hair tests can.
Australia's roadside drug testing programme has tested millions of drivers using oral fluid devices. The EU's DRUID project established 4 ng/mL THC in oral fluid as a suitable cut-off for roadside screening. The UK Misuse of Drugs Act 1971 Section 5a specifies 2 ng/mL whole blood THC for prosecution, but roadside screening uses saliva devices with laboratory confirmation. Understanding that delta-8 THC cross-reacts with standard THC immunoassays is important — delta-8 users may test positive on roadside saliva devices.
Saliva tests can be affected by food, drink, oral hygiene products, and certain medications. Eating or drinking before a test can dilute oral fluid samples. Some mouthwashes with high alcohol content may interfere with results. CBD products with trace THC can produce positive saliva tests shortly after use, especially for products with higher than stated THC content — see the full guide to drug test false positives. The test's short detection window makes it inappropriate for employment screening where historical use is relevant. The employment drug testing guide explains which methods employers typically choose.