I just got back from a multi-city trip.

I took a small bottle of OTC Miralax powder with me, as I had been on some pain medication from dental procedures.

At about 50% of the airports, I endured a bag check. Each time the culprit was the powder.

At one airport, a screener told me it showed up like a "liquid", another airport, the x-ray screener summoned 5 TSO's to look at the x-ray machine, they then whispered to each other in secret, as if they had "The Big Catch"(tm) and eventually called a bag check, and I had a couple other bag checks which were more routine.

Not sure what this stuff looks like on the x-ray, but at the other 50% of the airports I had no bag check, no second look...