How to test THC / CBD (cannabinoids): reduce risk by using a cannabis test kit to check it for adulterants. Cannabis products come in all kinds of forms and can’t be reliably identified by appearence. To test THC and CBD use the reagent tests Cannabis in single-use or multiple-use test kit. Reagent tests are simple chemicals that indicate presence of a substance by reacting with different color change to different substances. To test you need just 1 drop of a reagent and a small sample, about this big -> ●. To detect all ingredients and estimate potency it’s required to use the additional Cannabinoid test kit. To detect fentanyl or test for fentanyl analogs use the fentanyl test strips.