Much of the the known mechanics of digestion are molecular, but that's mostly due to the fact that we have a lot better scientific tools to deal with things on a molecular level than we do with macro-molecular constructs.

Granted the real issue is drinking more liquor because you don't notice how much liquor you have already drunk.

I recall hearing, also, that if you need both Calcium and Magnesium supplements they're better taken at separate times, as they compete for uptake due to both being +2 ions.

Without commenting on whether this applies to the case at hand: the medical term "potentiate" refers to one substance increasing the effects of another; one substance can also decrease the effect of another. Neither substance in isolation causes a problem, but the two taken together can cause harm.

One common example: you shouldn't drink milk or other high-calcium foods with some types of antibiotics (such as those based on tetracycline), because the calcium binds to the antibiotic and prevents absorption.

A less well-known example: drinking grapefruit juice with various different medications (such as blood-pressure reduction medications, some antihistamines, and some statins that lower cholesterol) can prevent the drug from breaking down as quickly, increasing the concentration in your system, such that it builds up as you take more. That interaction can kill you in various ways, such as increasing the effect of the drug in question, or destroying your kidneys.