http://mhlcoaching.typepad.com/the_health_and_life_mixin/2008/05/supplements.html

Vitamin, mineral and herbal supplements play an important role in our
health and well-being. However, because there is not FDA regulation
for supplements, it is important that you take a couple things in to
consideration when you're buying them:

1. Does it give you what you need?
Find out what the recommended daily allowances are for different
vitamins and minerals and make sure the supplements you are buying
meet those. If your supplement requires that you take three or four
just to get 100% of your daily requirements, you might be better off
buying a more expensive vitamin that you only have to take once.

2. Is the brand reputable?
Read some product reviews and make sure there are not major complaints
from other consumers. Look for brands that have been around for many
years and are known for quality.

3. Has your supplement been tested?
The company that makes it should be testing it in a laboratory setting
to make sure it is not only doing what it says, but also, so that it
doesn't cause damage. You can find out if your supplements are tested
by joining ConsumerLab.com