I understand your concern. The supplement industry is really being challenged these days (some good, some bad) and it is very confusing for consumers. The studies coming out are contradictory, and unless you know how to read studies and follow the scientific dialog, it looks like much of the information we've relied on relating to vitamins and health are being overturned. (Wouldn't be pharmaceutical money, would it???)
As far as vitamin, mineral and fatty acid supplements (like Omega 3's), there is never any counterindication nor side effects unless you are on a medication (like heart medicines that prohibit grapefruit). If your supplement is natural, balanced and whole, it's not an issue.
Herbs are natural medicines. Some herbs like St. John's wort, while very good, can interact with medications. Other herbs like alfalfa don't have any interactions at all.
Here are a couple of guidelines:
1) no synthetic vitamins. Make sure that the brand you are using is natural. Labelling law in the U.S requires only 10% natural product to get the natural label. That is deceit, IMHO. It is worth the time to write the company you are using.
2) make sure that the company you choose certifies (by a third party) that their supplements are free of lead, herbicides and pesticides.
3) make sure that the company you choose has bioavailability studies done by a third party. These studies prove absorption.
4) do not buy any multi-vitamin that has herbs in it. Those are popular b/c people think they are getting more for their buck, but we're talking molecular structure here. The amount of herbs in those products are miniscule. It is just a marketing tactic.
5) If you are buying a b-complex product, make sure that ALL 8 B vitamins are there in proper porportion. It must have 100% biotin. The B Vitamins work together, and they all like to "be at the party" at the same time.
Hope that helps.
Karen Miner Hurd