This page was last updated January 17, 2024

Use one teaspoon of water for every 10 mg of powder. This is 2 mg/mL.

2 mg/mL is the equivalent of one level micro scoop into one plastic bottle cap of water.
When using immunoassay test strips for drug checking (as opposed to urine testing), sample preparation is important. Any drug can produce a false positive if over-concentrated, and if you don’t concentrate enough (over-diluting by adding too much water) you run a greater risk of false negatives.
The proper dilution for any drug checking strip is initially determined by laboratory analyses as well as relevant facts about the current status of the illicit drug supply, such as the average concentrations of various adulterants in specific drugs. Over time, field testing supplemented by confirmatory lab analysis (like GC-MS) may change our understanding of the optimum dilution.
As of right now, we have determined that the optimum dilution for using WHPM’s xylazine test strips to test powdered illicit opioids is two milligrams per milliliter (2 mg/mL). This is the equivalent of 10 mg of powder into one teaspoon (5 mL) of water, or one level micro scoop into a normal plastic bottle cap.
This concentration is capable of detecting even tiny, microgram levels of xylazine, and it should not produce false positives even if the sample contains high concentrations of fentanyl, heroin, diphenhydramine, alprazolam, diazepam, etizolam, oxycodone, hydrocodone, or lidocaine.
Sensitivity
Two sets of studies have been conducted on these strips so far, one by WHPM (the manufacturer) and one by Dr. Marya Liebermann at the University of Notre Dame. These preliminary studies have demonstrated that WHPM’s xylazine test strips can reliably detect xylazine at concentrations as low as 2,000 ng/ml of water, which is extremely sensitive. This means that, if used according to our instructions, an illicit opioid sample containing just 1% xylazine would have a xylazine concentration 1,000 times greater than the minimum detection limit, making false negatives very unlikely.
Potential False Positives
Immunoassay test strips can sometimes cross react with drugs other than the target substance (xylazine, in this case), especially at higher concentrations. False positives, therefore, are always a concern. The good news is that current laboratory studies on WHPM’s strips have shown promising results. So far, the following substances have been tested:
- Fentanyl
- Heroin
- Diphenhydramine
- Alprazolam
- Diazepam
- Etizolam
- Oxycodone
- Hydrocodone
- Lidocaine
These substances were selected for testing because of their prevalence in the illicit opioid supply, and none of them cross-reacted at concerning concentrations. As long as the strips are used according to our instructions, this means that these drugs should not produce false positives.
Of course, the list of drugs that are sometimes found in illicit opioids is long, and most of them have not yet been tested. This means false positives are still possible with all xylazine strips on the market today. We are currently working with W.H.P.M., as well as two University laboratories, to test as many additional common cuts as we can as quickly as we’re able. Check back here often, as we will be continuously updating this page with any new information we get as soon as it becomes available. (Refer to the top of this page to see the date of the latest update.)