FDA/FoodGrade ONLY means the FDA says it won't kill you ... 'it's ok as a food' - doesn't guarantee it's pure or fresh. Pharma grade is what prescriptions are required to be -> 99.9% what's on the label, and supplements can be pharma grade -> it's the only kind of supplement I buy.
I'm not a doc but learned this distinction from a (real) nutritionist. Welcome people to challenge or refine it.
But just because it's on Walmart's shelves in a fancy schmancy RX looking bottle doesn't mean it's pure-what-it-says-it-is.
I recommend a site called labdoor.com for rating purity of various supplements.
Good luck and prayers!
Thank you and thanks for your prayers