knock
Bluelighter
As a rule of thumb, chemicals are less stable in solution than as a solid.
I didn't realise this was a general rule. Just to be clear, when I described PG as a preservative, I meant in the sense of food preservative, i.e. it doesn't provide a friendly environment for micro-organisms like mould. I didn't mean it would preserve the structure of drug molecules.
Is there any way, like a rule of thumb and maybe a finger or two, for a layman like me to work out how stable some specific chemical would be, dissolved in PG? Other than trying it out.