I had a dietitian tell me that I should never buy vitamins from places like Walmart, Walgreens, or similar stores because the potency is never guaranteed. She said that the potency greatly varies from pill to pill and sometimes is only 25% as potent as listed on the label.
She directed me to online stores that sell awfully expensive vitamins that "guarantee" the potency. I checked the nutritional labels between both the Walmart and "designer" brands and they both have the exact same dosage per pill, the only difference is brand and price.
Her claim is that I'm simply wasting money on these generic vitamins and I am simply taking a pill that mainly contains inert ingredients.
I worked in the breakfast foods industry for a few years and I know that the FDA would be all over us if we lied on our product labels.
Is there any evidence that the generic, cheap vitamins are less potent than more expensive vitamin preparations?