Traces of fentanyl can stay in your system for a lot longer than it takes for the effects of fentanyl to wear off. Drug testing can detect fentanyl or its metabolites (breakdown products) in urine for 24 to 72 hours, in blood for 5 to 48 hours, and in hair for up to 3 months, but it cannot be consistently detected in saliva.
Fentanyl has a half-life of 7 hours and experts usually agree that it takes 4 to 5 half-lives for a drug to be cleared from your body (which calculates to 35 hours). However, the actual length of time fentanyl stays in your system depends on what dose you took and how you took it (for example, by injection, via a patch, or orally), if you have been taking it for a long time, your weight, what other medications you take, and if you have kidney or liver disease. Someone using the drug once or twice can process and remove fentanyl much faster than someone who uses high doses consistently.
What is fentanyl?
Fentanyl is a synthetic opioid that may be prescribed for difficult-to-treat pain. The prescription version may come in the form of a tablet, lozenge, or patch, but fentanyl may be used illegally to lace other substances, such as cocaine.
Note that doses are not equivalent between the different formulations (for example a 25mcg fentanyl patch DOES NOT EQUAL 25mcg of fentanyl injection). The substitution of one fentanyl product for a different type of fentanyl product (for example Subsys for Duragesic) may result in a fatal overdose. It is always safer to underestimate fentanyl requirements.
Fentanyl is a schedule II-controlled substance that is up to 100 times more potent than morphine on a weight-for-weight basis. Overdose is a serious concern with fentanyl, particularly since it is often combined with other substances including alcohol. Respiratory depressant effects can be seen from as early as 15-30 minutes after administration and persist for several hours.
Fentanyl has a high potential for abuse and may be used to covertly lace counterfeit drugs. Several deaths have been reported in people unknowingly consuming fentanyl, for example, from Xanax-laced with fentanyl.