Shouldn't you be asking your doctor that? And also whether you, particularly, should take such a supplement?

I know this will be an unpopular opinion but Magnesium is conventional enough of a supplement that you can easily get away with trying it on your own without consulting a physician.

If you want to be extremely strict, sure, but that supplement is already in various foods that people take daily.

do you consult your doctor before trying a different brand of coffee?

If merely trying a new brand can cause a medical condition worthy of its own name or if it can have adverse effects depending on other medical issues I might have, then yes: https://en.wikipedia.org/wiki/Hypermagnesemia

Do you take all kinds of vitamins and supplements with this cavalier, throw caution to the wind, attitude, or just magnesium because you happen to know it's tame enough? Before supplements don't always bode well with existing conditions, or even with high dosages.

there are instant coffee brands with extra caffeine added in as well... you can die from drinking the previous quantity of this new brand of coffee!

>you can die from drinking the previous quantity of this new brand of coffee!

Obviously almost everybody knows about coffee and has already tried many brands in their life (even by going to different restaurants or coffee shops) -- including days when they've drank several times their usual intake. Plus, they've seen countless others doing the same, even before they've started drinking themselves (e.g. their parents).

With magnesium or some random supplement? Not exactly the same case.