I learned this with Proton Pump Inhibitors. I was not responding at all to the normal dose, and all my gastro said was to keep taking it. It was my pharmacist who advised me to double the dosage at which point I started seeing improvement.

23andme testing eventually told me I was a "fast metabolizer" and would likely need a higher than normal that dosage.

I'm glad at least my pharmacist was on top of things.