Be careful about prophylaxis if you are at low risk. Nutritional supplements with no known issues of significance are always good as being deficient in any of those is always bad.

But -- pharmaceuticals are another matter. None of them is without risk. If you are at high risk then the calculation is a different matter, but for those who are not I caution that playing around with drugs in this fashion is like playing with recreational pharmaceuticals -- they may harm you and they may not, but the benefits are likely non-existent.

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