BTNX Rapid Response Fentanyl Test Strips are the only test strips recommended by a 2018 John Hopkins University Study. The technology was developed in Canada and tests for a comprehensive list of common fentanyl analogues. Testing for Fentanyl in powders, liquids, & urine is a harm reduction strategy. Fentanyl Test strips offer an easy and quick way to test powders and liquids for the presence of many Fentanyl analogues with no more than sterile water. These Fentanyl test strips come individually packaged for your convenience and safety. These tests were originally designed as urine tests but are endorsed by BTNX to work with many powders (diluted in water) and liquids with 98% accuracy. You can visit the manufacturer website for many videos and documents to support this including the 2018 John Hopkins University Study.