How long can cannabis be detected in a drug test?

Cannabis Detection Windows in Drug Testing

Cannabis can be detected in urine for 1-3 days after occasional use, but extends to 30 days or more in heavy, chronic users. 1

Detection Times by Testing Method

Urine Testing (Most Common)

The detection window for cannabis metabolite 11-Nor-9-carboxy-THC (THCCOOH) varies dramatically based on usage patterns: 1

• Infrequent users (less than 7 g/month): Detectable for approximately 2 days after last use 2
• Moderate users (approximately 28 g/month): Detectable for an average of 4.7 days (range 2-8 days) 2
• Heavy chronic users (approximately 56 g/month): Detectable for an average of 13 days (range 9-25 days), with some cases extending 30 days or more 1, 2
• Extreme chronic use: Detection up to 3 months has been documented 3

Blood Testing

Blood testing detects active THC and has much shorter windows: 1

• Occasional users: THC typically undetectable after 1.5 hours following inhalation 4
• Frequent users: THC may be detected for up to 30 days in chronic heavy users 4
• Blood concentrations are most useful for detecting use within 2-12 hours and correlate best with impairment 1

Saliva/Oral Fluid Testing

Saliva detects recent cannabis use with intermediate detection windows: 1

• Generally detects use within 24-48 hours 1
• Frequent heavy users: THC detected for up to 8 days after cessation 5
• Important caveat: Positive samples can be interspersed among negative samples several days after cessation in chronic users 5

Hair Testing

Hair provides the longest detection window but cannot detect recent use: 1

• Cannot detect use in the previous 7-10 days 1
• Standard 3 cm sample covers approximately 90 days 1
• Most reliable for heavy, frequent past use, not occasional use 1
• False positives possible from environmental contamination with volatile cannabis 1

Sweat Testing

Sweat patches offer continuous monitoring: 1

• Patches worn 3-7 days detect use just before application and during wear period 1
• Most drugs excreted within 48 hours 1

Critical Clinical Considerations

Factors Affecting Detection Time

The following variables significantly impact how long cannabis remains detectable: 1, 3

• Frequency of use: Single most important factor
• Quantity consumed: Higher doses extend detection
• Potency of cannabis: THC concentration matters
• Urine concentration: Dilute specimens may cause false negatives 6
• Individual metabolism: Significant person-to-person variation 3

Common Pitfalls to Avoid

Synthetic cannabinoids (K2, Spice) will NOT be detected on standard cannabinoid screens and require specialized testing 6

Negative tests do not exclude use - timing relative to last use is critical, and most drugs have detection windows of 72 hours or less (except cannabis in chronic users) 6

Interpreting chronic users: Differentiating new intake from residual excretion requires quantitative THCCOOH measurements corrected for urine dilution and time between collections 1, 3, 2

Adulteration risk: Urine samples can be tampered with using bleach, vinegar, salt, or soap to produce false negatives 2

Best Practices for Testing

Verify testing panel contents before ordering - not all panels test for the same substances 1, 6

Consider confirmatory testing with gas chromatography/mass spectrometry when results are unexpected or will impact clinical decisions 6

Monitor chronic users by following quantitative THC-to-creatinine ratios over time to distinguish ongoing use from prolonged excretion 1

Consult laboratory personnel or toxicologists before making clinical decisions based on unexpected results 6

For suspected recent use in chronic users, a combined criterion of THC ≥5 μg/L plus THCCOOH/11-hydroxy-THC ratio <20 provides detection windows under 8 hours after use 4