In this day and age everybody has heard of vitamins and supplements, and probably have also heard recommendations to take certain ones for different reasons. I have recommended plenty in my years of practice with much success, especially where other strategies might have failed!
The problem with supplements is they are not yet regulated by the FDA, so essentially it can be like the "Wild West" when trying to choose a reputable brand. The industry recognized this and realized the consumer (and healthcare provider) could not always differentiate good companies from not so good companies. Many things will influence the effectiveness of a supplement including accurate measurements, raw goods used, and contamination with other substances (ie, heavy metals or potential allergens).
I want to introduce you to a link that has a list of many reputable companies that carry a "gold standard" certification called GMP (Good Manufacturing Standards). It's one of very few "checks and balances" that the supplement world can offer to help differentiate a good quality company from a poor quality company. I have enclosed a website that has a list of over 300 companies that have went through the time and expense to get certified (pricing can many times reflect quality). It's at least a good place to start your research!
Yours in Good Health!