As I see it, the main problem with supplements marketed to runners is that the industry is unregulated by the FDA, unlike drugs. And make no mistake, this is a huge industry. One source estimates that yearly sales hover at estimated at over $17 billion.
With no real way to know what are in those supplements means you may be wasting money, not getting the results you expect, or in the worst case you could be harming yourself. If you decide to roll the dice you can only put faith in manufacturer's claims. Even if the claim is made that "studies have shown blah, blah, blah," in may cases the study has been funded by that very same manufacturer.
Many ads sound downright bizarre. For example, for a while now a supplement made from jellyfish claims to help brain function. By all rights jellyfish should be swimming Einsteins. But they're not.
This isn't to say that all the news is bad. Vitamins and some herbal supplements have undergone legitimate studies and do offer many benefits. Many have been independently tested and bear a label on the bottle. For example, Consumerlab.com says, "To further help consumers,
ConsumerLab.com allows manufacturers and distributors to use specific CL
Seals to identify products that have met ConsumerLab.com standards
based on its product reviews."
The bottom line? Be skeptical and do your homework before shelling out that hard-earned money.