Adrenals & Vitamin C

I believe Magnesium has helped somewhat to improve my adrenals so now I am going to try adding in vitamin c. However I have read that vitamin c "reduces" cortisol (hormone produced by adrenals)which is good if your adrenals are producing too much but if you already have low cortisol levels adding in vitamin c can actually make the adrenal function worse? Is it best to have tests to check cortisol/adrenal hormone levels before randomly throwing in high dose vitamin c. Anyone felt worse taking high dose vitamin c?

Thanks