What we checked
We tested 36 batches of fentanyl strips from 20 companies and 20 batches of xylazine strips from 10 companies. Lab members have sent in 175 test reports so far.
How they did
Most of the time, the strips worked. In plain water, fentanyl strips were right 99.7% of the time. When fentanyl was there, they found it about 8 in 10 times.
Xylazine strips gave a clear answer in about 7 of 10 tests. About 35% of tests gave a faint line that was too hard to call.
Two limits worth knowing about
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Faint test lines. At low amounts, some strips show a very faint test line
Example of a very faint test line (see the arrow).. It is easy to miss, especially in poor light. For fentanyl strips we count any visible line as a negative result. For xylazine strips we call a faint line “inconclusive.” -
False alarms from other drugs. Sometimes a strip says it found the drug when it did not. For fentanyl strips, diphenhydramine (Benadryl) is the most common reason (18 of 36 batches). For xylazine strips, similar medicines like romifidine, tizanidine and clonidine can do it.
Even so, 16 of the 36 fentanyl batches found fentanyl every time and never gave a false alarm in plain water.