Fentanyl and Norfentanyl Detected in Urine for 7 or More Days After Regular Use

Illicit opioids in the US are increasingly found to contain fentanyl (or analogues), contributing to recent increases in overdoses due to its higher potency. After one or a few doses, fentanyl is cleared from the body after 2–4 days. However, it is highly lipophilic and with regular use may become sequestered in adipocytes (fat cells) or other tissues, leading to prolonged clearance. In this study, researchers serially tested the urine of 12 participants with opioid use disorder in a 28-day residential program who tested positive for fentanyl at baseline.

  • The mean time for clearance of fentanyl was 7 days and norfentanyl (a metabolite) 13 days after last use.
  • One participant continued to test positive for fentanyl for 19 days and norfentanyl 26 days after last use.

Comments: These observations may have implications for treatment of individuals with opioid use disorder and may explain reports of difficulties with initiation of buprenorphine due to precipitated withdrawal in individuals using fentanyl. We need more research on optimizing buprenorphine initiation for individuals with fentanyl use and investigations of alternative approaches such as using tramadol (or other opioids) as a bridge (limited by regulations in the US), or the use of low doses (which some call “microdosing”) of buprenorphine, which may involve use of buprenorphine formulations not approved for opioid use disorder.

Darius A. Rastegar, MD

Reference: Huhn AS, Hobelmann JG, Oyler GA, Strain EC. Protracted renal clearance of fentanyl in persons with opioid use disorder. Drug Alcohol Depend. 2020;214:108147.


  1. This is good information to get. I have a patient who has been testing positive for the metabolite Norfentanyl for 35 days since her last use. It is consistently dropping, but has not entirely disappeared yet.

    1. Can one do an induction to suboxone with the norfentanyl metabolite still in thier system? Or in your experience, does the patient still go through precipitated withdrawals when there is any trace of the metabolite present?

  2. THANK YOU. Im an addict in recovery and this answers alot of my own and other peoples unanswered questions like why suboxone still put ppl into precipitated withdrawal even after waiting 3 days or why withdrawal seems to take 2 weeks sometimes but the facts are telling us fentanyl clears faster than heroin. Now we know it does yes but with regular use it builds up in fat cells much like marijuana.

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