Content reviewed by the PillRelax Healthcare Team | Last reviewed: September 2026
Diazepam is one of the longest-acting benzodiazepines available. Understanding how long it remains in your body is important for safety, drug testing, and medication management.
Diazepam Half-Life
Diazepam has a plasma half-life of 20 to 100 hours. Its primary active metabolite, desmethyldiazepam, has an even longer half-life of 36-200 hours. This means a single dose can produce active effects and remain detectable for several days.
How Long Is Diazepam Detectable?
| Test Type | Single Dose | Prolonged Use |
|---|---|---|
| Urine | 3-7 days | Up to 6 weeks |
| Blood | 6-48 hours | Up to 7 days |
| Saliva | 1-10 days | Up to 10 days |
| Hair | Up to 90 days | Up to 90 days |
Factors Affecting Duration
- Dose and duration of use – higher doses and longer treatment = longer detection
- Age – older adults metabolise Diazepam more slowly
- Liver function – impaired liver function prolongs presence
- Body fat – Diazepam is highly lipophilic, accumulates in fatty tissue
Driving and Diazepam
Under UK law, driving while impaired by Diazepam is illegal. The UK has a strict threshold for Diazepam in blood (550 micrograms/litre). Do not drive while taking Diazepam without explicit medical clearance.
Frequently Asked Questions
Does water flush Diazepam out faster?
Increased hydration has minimal effect on elimination. Diazepam is metabolised in the liver, hydration does not significantly change metabolic rate.
