Schneiderman said that only 4 percent of Walmart’s supplements (“Spring Valley” brand) actually contained the ingredients listed on the label, while 18 percent did at Walgreens (“Finest Nutrition” brand), 22 percent at GNC (“Herbal Plus” brand), and 41 percent at Target stores (“Up & Up” brand). Only the GNC garlic consistently tested as advertised, according to the AG’s office.
A research letter published in JAMA Internal Medicine (free full text) a few years ago on a bunch of OTC Vitamin D supplements showed similar variability, ranging from 9% to 146% potency.
That’s the #1 reason I have accepted only prescription Vitamin D (and now B12). If it’s important enough for my doctor to recommend, then it’s important to me that I get the amount I need!
Edited to fix opening quotation formatting that broke when posting from my phone earlier.