Here's the problem, the best quality supplements are expensive. The ones you're buying are cheap. So it depends on how much you want to spend on this and also on what you're taking. No one company is great at everything -- the more you know about the companies who market supplements, the more you realize each one is good at certain things and not so great at others, or too expensive at some things for what you're getting. Now, all supplements in pill form are going to have fillers and binders, the capsule or the tablet has to be made out of something. Which ones are used depends on how much money the company decides to spend on it -- the more you don't want it the cheaper it probably is. Another factor is where the nutrients are sourced -- really expensive supplements are often expensive because they are very careful about where they get the raw materials for their supplements. Cheap ones usually just buy on the open market from whoever is wholesaling what they're putting in their supplement and have no input (and don't care) about where it's coming from. Some sources are a lot more likely not to have contaminants than others, especially with, say, Chinese herbs. You don't say what you're using. Some nutrients are only made by one or two places so everyone is buying pretty much the same thing, such as vitamin C and E, but there still can be different fillers and binders and they are still made in different forms, some of which are more like what you find in food than others. Some companies go very far in trying to make something closer to food than other companies -- Mega Foods and New Chapter are examples of very expensive supplements that claim to have a way of taking an isolated supplement and turning it back into something more like food. A store that's pretty reliable is Whole Foods, but its selection isn't that great and it does carry discount brands -- if you want pure don't buy discount brands unless they have a really good reputation and that reputation is current. There are stores online that carry nearly everything you used to find on the shelves of the really good health food stores that Whole Foods and other large chains have put out of business, such as Vitacost and Iherb. They run a lot of sales that can bring down the price, but you still have to know which brands to buy. Also generally avoid store brands, again, don't care about the source, only care about price. Bottom line, to answer the question, one would have to know everything you're taking, because again, there's no one company that's great on everything. I can pretty much guarantee, though, that except for the most basic of vitamins such as D3, C, and E, and again, even there they come in different forms and only some forms are actually useful, buying supplements at discount clubs won't get you anything of high quality. They wouldn't know a good vitamin from a bad one, it's not what they do.