I would steer clear of these if I were you. Except for the very basic and long tested ones - such as vitamin C, perhaps. Or the ones that are in fact advertised as drugs.

The FDA doesn't screen dietary supplements. They are treated as food, which means they can make it to store shelves with little or no testing. And since they aren't screened bad things can happen with them, such as them being spiked with undeclared drugs. Granted that's a weight-loss supplement, but there have been many examples of a variety of supplements making it to store shelves - only to have the FDA eventually discover they are harmful. A list of said supplements which the FDA is concerned about, but which may still be on the market can be found here.

Even aside from safety concerns, there are concerns about the effectiveness of dietary supplements. It is unknown exactly how well they are absorbed by the body in the forms provided in the supplements. Often it is the case that the vitamins and minerals provided in supplements are simply in a form the body doesn't and can't use very well. As a result most of it just passes right through you.

Better to play it safe and just be sure you eat a wide and varied diet that contains a little bit of everything and a lot of veggies - particularly raw veggies. Raw vegetables are among the best sources for vitamins and minerals out there. And you will often absorb far more of the nutrients they contain than you would absorb the nutrients from a pill of some kind. If you're curious about the nutrition contained in a certain food, and interested in ensuring you get enough of a certain nutrient, take a look at the wikipedia article on that food. Often they contain small "nutrition information" boxes that tell you how much of each nutrient is contained in 100 grams of that food (mostly this is done for fruits and vegetables).