how long fentanyl stay in your system
If you are taking a drug test and you are concerned about the levels of fentanyl, the levels will vary depending on the testing method. For example, urine can detect fentanyl eight to 24 hours after use. Blood tests can only accurately test up to 12 hours, while saliva can detect levels of fentanyl for up to two days. Hair follicle tests, however, can detect the use of fentanyl for up to 90 days, because the drug may have cleared your system, but will still be present in your hairs for three months. 1  The amount of time it takes for a drug to leave your system is based on the half-life of the drug.