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.