I tested another vitamin C from the cupboard and found it was good for me. That was plain ascorbic acid. The vitamin C that was bad for ME was derived from rose hips. These range from mild to severe. For many drugs, there are yet undiscovered side effects.
Bodies are different.
Here's How to Tell For most of you this is going to be weird. Just try it. It works whether you believe it will or not. But it may take a few minutes of practice. Pick up a product you want to test.