http://www.usp.org/usp-verification-...ry-supplements
Look for the USP logo on dietary supplements. Europe also has an inspection program.
http://www.usp.org/usp-verification-...ed-supplements
Just because an item is "inspected" it does not always translate to safe. The current chicken/salmonella problem is a good example. The toxic mold that contaminated steroid injections and killed 55 people is another example.
It doesn't hurt to read up on a supplement and the company that produces it before purchasing it. As an enthusiastic supplement user, I can say I've bought a lot of supplements. I always start out taking much less than recommended to see how my body reacts. I learned the hard way when a family member sent me a box of supplements and told me to take 2. I was through the roof, she was barely affected. I needed 1/20th of the amount to get the same benefits.
I love reading the stories about how people's lives drastically change because of a supplement. But it typically doesn't translate to the individual because dietary needs are different. Many times you are just spending money on another bottle that will be tried, then sits on the shelf.
Twice, however, I've had dramatic changes in my health due to supplement use. The first was with selenium after many surgeries. I had excruciating fatigue and brain fog that was so bad I was pretty much inop. I experimented with the selenium after much reading on the internet. My fatigue and brain fog resolved significantly over the next few hours after the first tablet. I kept taking it and was back to my old self within days.
Kelp eliminated breast pain that was a 10, even after taking Tylenol. Within hours. I had to take it for a couple years, and still am hesitant to stop taking it.
I feel that when I try a supplement - I am a clinical trial of 1 - the principal investigator, the clinical trial nurse, and the patient, all rolled up into one.