Gabi asked
I go to a methadone clinic and I have been clean for 8 months. Twice though, through urine testing, I have tested positive for fentanyl (not in a row). The first time I waited and gave a second sample and the second sample was negative. The 2nd time I had an appt and couldn't stay to give a 2nd sample. However I did give a swab which of course came back negative for fentanyl. I cant figure it out... I don't know what is going on. Please help me!!! I take melatonin, buspirone, clonidine, topiramate, prazosin and hydroxyzine. This is the 2nd time so I have a feeling it's going to keep happening. Thanks for any help you can provide.
At a glance
- Urine drug screens usually don’t look for the drug directly, they screen for known metabolites.
- False positives do occur. Many labs use a different test. They may have on file certain drugs which may register a false positive. Provide your current medication list as well as any herbals or supplements to the lab or the person that ordered the test.
Answer
Hi Gabi and thank you for your question.
I did a bit of digging but unfortunately I don’t think I will be able to provide you with a definitive answer. When it comes to urine drug screenings, they usually aren’t specifically looking for fentanyl in your urine. They are looking for a known metabolite, or a known end product that your body would turn fentanyl into before you urinate it out. That metabolite is a bit of a mystery as there are several different screening tests available on the market. Most of these tests are going to be a little bit different, so I have no real way of knowing what metabolite the lab is looking for.
Due to the fact that a urine drug screen is only looking for a metabolite and not the actual drug itself, similar metabolites, sometimes from unrelated drugs may cause a false positive. Most labs may have a reference file of drugs that may cause a false positive. If I were in your shoes, I would provide the lab with a list of drugs that you are presently taking, as well as any over the counter herbals or supplements. One of these drugs may be causing a false positive reading.
For some more information, you can take a look at another answer one of our pharmacists has written on this very subject, and he goes into a little more detail on why fentanyl is somewhat different from other opioids as it concerns drug tests, but still can come up as a false positive:
What Drugs Cause Fentanyl False-Positives?
I hope that helps and feel free to write us back in the future!
References
- False-Positive Interferences of Common Urine Drug Screen Immunoassays: A Review, Journal of Analytical Toxicology
- Cross-Reactivity of Acetylfentanyl and Risperidone With a Fentanyl Immunoassay, Journal of Analytical Toxicology
