Fake weed aka potpourri can be addictive? right?

Yes: Substances do not have to cause a physical dependency in order for them to cause addiction. In addition, with many of the synthetics, the chemicals involved are sprayed onto inert plant material. This process often results in uneven deposits of the active drug. A person will smoke some, not get much of an effect, so will take more, and may get an area of higher concentration of drug, and get sick.