YES! These Kits are purely a presumptive test. Each EZ Test kit can only check for the presence of one specific substance or a group of substances and will not indicate the presence of other substance (s) or adulterant (s),that could be contained in the same sample.
There is also an obvious question regarding the subjective nature of the colour charts and how they can be interpreted. There are valid arguments against the use of presumptive testing kits. It is widely understood that only gas chromatography-mass spectrometry (GC-MS), High Performance Liquid Chromatography (HPLC), or similar laboratory techniques can satisfactorily identify the full array of substances that might be in one pill or powder.