I finally found a good thread on this subject for anyone interested: here. KSman lays it out, stating that anastrozole is soluble in alcohol but not water, and that the solids I’m seeing are in fact filler, as @naysayyer said.
One other important piece of information is that the number of drops per mL in a given dropper will be different when using vodka vs. water. This means I need to adjust my dosing because I’ve been using a dropper that dispenses at 56/mL of water, but only 43/mL of vodka. In other words, I’ve been overdosing by about 25% for the past week!