Fairy-dust threshold
Our own reference cutoff (not an official regulatory term): 20% of the low end of the studied dose range in our reference data. A product declaring less than that is unlikely to reproduce any tested effect. It still legally lists the ingredient; it just does so at a token amount. A few compounds have no threshold.
Example
33.2% of on-market magnesium products fall below magnesium's fairy-dust threshold of 48mg (20% of the 241mg low end of its studied dose range).