The SM we order from, if you've agreed, will deliver substitutes for the same cost, even if larger or dearer.
Substitutes are recommended by computer, often completely bizarre and unrelated to what you ordered.
We no longer ask for substitutes as too many things react with my mums medication so she has to be extremely specific.
For example all the sugar free drinks have a chemical in them that is iffy. (likely for everyone as its not been well tested, but worse with her medication) Its pretty much original Pepsi or nothing, soft drinks wise, which can be problematic with takeaways when they are out of stock so try to sub it for something sugar free.