How long do benzodiazepines (Benzos) stay in urine?

Detection Time of Benzodiazepines in Urine

Benzodiazepines can typically be detected in urine for 1-7 days after use, though this varies significantly based on the specific benzodiazepine, dosage, frequency of use, and individual metabolism. 1

Detection Windows for Common Benzodiazepines

Short-Acting Benzodiazepines

• Alprazolam (Xanax)
  • Detectable in urine for up to 2.5 days after single use 2
  • In experimental studies, median detection time was 36 hours for its metabolite α-OH-alprazolam 3

Intermediate-Acting Benzodiazepines

• Clonazepam (Klonopin)
  • Detectable in urine for up to 5-6 days 2
  • Its metabolite 7-aminoclonazepam can be detected for up to 14 days in all subjects after a single 3mg dose, with some individuals testing positive for up to 28 days 4

Long-Acting Benzodiazepines

• Diazepam (Valium)
  • Detectable in urine for up to 7-11 days after single use 3
  • Metabolites like oxazepam may be detectable for up to 11 days (median 252 hours) after a single dose 3
  • In heavy users, detection times can be significantly longer 2

Factors Affecting Detection Time

1. Specific Benzodiazepine Properties

   • Half-life varies significantly between benzodiazepines
   • Diazepam has a terminal elimination half-life of up to 48 hours, with its active metabolite N-desmethyldiazepam having a half-life of up to 100 hours 5
   • Alprazolam has a shorter half-life of approximately 11.2 hours (range: 6.3-26.9 hours) 6

2. Patient-Specific Factors

   • Age: Elimination half-life increases by approximately 1 hour for each year of age beginning with a half-life of 20 hours at 20 years of age 5
   • Liver function: In patients with alcoholic liver disease, half-life can range from 5.8 to 65.3 hours (mean: 19.7 hours) compared to 11.4 hours in healthy subjects 6
   • Body composition: In obese individuals, half-life can be significantly prolonged 6
   • Genetics: Genetic polymorphisms can lead to extremely prolonged detection times, with one case report showing oxazepam detected 79 days after diazepam withdrawal 7

3. Usage Pattern

   • Chronic users will have longer detection times than single-dose users 8
   • Heavy drug abuse can result in detection for extended periods 2

4. Testing Method

   • Standard immunoassays may not detect all benzodiazepines equally 1
   • Confirmatory testing with GC-MS or LC-MS/MS provides more accurate results 1

Clinical Implications

• When testing for suspected benzodiazepine use in cases like sexual assault, collection timing is critical - flunitrazepam (Rohypnol) can be found in urine for up to 48 hours after ingestion 9
• For date-rape drugs like flunitrazepam, samples should be collected as soon as possible to ensure detection 9
• Standard drug screening panels may not detect all benzodiazepines; specific testing may be required 9
• False negatives can occur if testing is performed outside the detection window or if the specific benzodiazepine is not included in the test panel 1

Important Caveats

• Detection times can be significantly longer in chronic users - up to several weeks in some cases 8
• Extreme outliers exist - some individuals may test positive for much longer periods due to individual metabolic variations 7
• Most benzodiazepine screens identify oxazepam and may not detect all benzodiazepines equally 9
• When evaluating a patient for benzodiazepine use, it's important to know which specific drugs are included in the test panel 9

Remember that these detection windows represent general guidelines, and individual variations can significantly affect how long benzodiazepines remain detectable in urine.