What this test measures
Tetrahydrocannabinol (THC) is the main psychoactive component of cannabis. After smoking or ingestion it binds CB1 receptors in the brain, producing euphoria, altered perception, impaired coordination, and short-term memory disturbance. Two related measurements are used: the parent compound delta-9-THC (indicates very recent active use — last few hours) and the inactive metabolite 11-nor-9-carboxy-THC (THC-COOH), which lingers for days to weeks.
The initial test is an immunoassay; positives are confirmed by LC-MS/MS. Urine tests detect THC-COOH and have a much longer detection window than blood tests.
Why it matters
In India, cannabis (charas, ganja, bhang) is regulated under the NDPS Act 1985, though bhang remains legal in some states for ritual use. The THC test is requested in several contexts. Workplace and pre-employment screening — particularly transport, aviation, and safety-critical roles. Emergency assessment of suspected impairment after a road accident or unexplained altered mental status. Forensic analysis in custody and post-mortem cases. Confirming abstinence in addiction-medicine programmes.
The distinction between active impairment and historical use is important. A positive blood THC (parent compound > 1 ng/mL) suggests recent use within the past few hours. A positive THC-COOH metabolite without parent THC suggests use days to weeks ago — consistent with passive presence in the body but not with active impairment at the time of sampling.
How to prepare
No fasting required. For workplace or forensic submissions, follow chain-of-custody: photo ID, sealed container, tamper-evident seal. Avoid second-hand cannabis smoke for 48 hours before the test where possible. Disclose any prescribed cannabinoid medications (rare in India) and any hemp-seed or CBD products — some can produce low-level positives. Drinking large amounts of water before a urine test does not reliably "wash out" THC and may flag the sample as dilute.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| Delta-9-THC (Parent) (ng/mL)[1][2] | Not detected (typical cut-off 1–2 ng/mL serum) | Not detected: no recent active cannabis use (within the past several hours). | 1 – 5 ng/mL: recent use within hours; mild impairment possible. 5 – 10 ng/mL: clear recent use; many jurisdictions use 5 ng/mL as a driving-impairment threshold. > 10 ng/mL: very recent heavy use; significant impairment likely. |
| THC-COOH (Metabolite) (ng/mL)[1] | Not detected | Not detected: no cannabis exposure within the recent past (days to weeks depending on use pattern). | Positive: confirms cannabis exposure. Detectable in occasional users for 3–7 days; chronic heavy users 30+ days. Presence of the metabolite alone (without parent THC) means historical use, not necessarily current impairment. |
THC detection windows by specimen and use pattern
| Specimen | Occasional user | Daily chronic user |
|---|---|---|
| Blood — parent THC | 1 – 6 hours | 24 hours |
| Blood — THC-COOH metabolite | 1 – 3 days | 7 – 30 days |
| Urine — THC-COOH | 3 – 7 days | 30 – 60 days |
| Saliva | 24 – 48 hours | 72 hours |
| Hair | Up to 90 days | Up to 90 days |
Frequently asked questions
What is the difference between THC and THC-COOH?
THC (delta-9-tetrahydrocannabinol) is the active drug — its presence in blood suggests recent use and possible impairment. THC-COOH is the inactive metabolite — it persists for days to weeks after use and indicates exposure but not impairment at the time of testing.
How long does cannabis stay detectable in blood?
The parent THC: 6–24 hours after a single use, up to a couple of days in chronic heavy users. The THC-COOH metabolite: 1–7 days in occasional users, up to 30 days in chronic daily users.
Can second-hand cannabis smoke cause a positive?
It is possible but uncommon at standard screening cut-offs. Heavy exposure in an enclosed space could produce a low-level positive — most workplace cut-offs are set high enough (50 ng/mL THC-COOH urine) to minimise this.
Is bhang legal in India?
Bhang — a preparation of cannabis leaves — falls outside the NDPS Act and is legal in many states, particularly around festivals. Charas (resin) and ganja (flowering tops) are controlled substances. Drug tests do not distinguish the source.
Can CBD or hemp products cause a positive?
Pure CBD products do not test positive for THC, but many over-the-counter CBD oils, especially full-spectrum products, contain small amounts of THC and can produce positives with regular use. Hemp-seed foods can occasionally trigger a low-level positive.
What is the impairment level for driving?
India does not have a legal blood-THC cut-off for driving — impairment is judged clinically. Some Western jurisdictions use 2 ng/mL (Germany) or 5 ng/mL (Colorado, Washington). Above 5 ng/mL active THC, impairment is generally clear.
Why does the urine test detect cannabis for so much longer?
THC is highly lipid-soluble — it stores in body fat and slowly releases back into blood, where it is metabolised and excreted via urine. In chronic users this can keep the urine THC-COOH detectable for a month or more after stopping.
Related Drugs / Therapeutic Monitoring tests
Tests commonly ordered alongside TETRAHYDROCANNABINOL, or that help interpret an unexpected result.
Sources & references
- NCBI StatPearls — Cannabis Use Disorder · accessed 2026-05-30T00:00:00.000Z
- NIH NIDA — Cannabis · accessed 2026-05-30T00:00:00.000Z
- Mayo Clinic Labs — Cannabinoids (THC), Serum · accessed 2026-05-30T00:00:00.000Z
- CDC — Marijuana and Public Health · accessed 2026-05-30T00:00:00.000Z
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