Anyone who has enough money to do a "scientific study" is most likely biased one way or another. Where did the money come from? The world we live in today is commercially driven. The money most likely comes from one of two scources, someone who is marketing product "A" and wants to present it as effective, or someone who is marketing product "B" and wants to present product "A" as ineffective and possibly dangerous because the successful marketing of product "A" would dramatically have a negative effect on the marketing of product "B". These studies can easily be done, manipulated, or presented in a way that shows the desired results.
So who do you trust? Do you turn your trust to government watchdog agencies that are run by people who have ties and interests in product "B"?
Do your own "study". Research and take note of what those who have tried a product have to say about it, what they have experienced. How long has it been in use by the public, have there been reports of side effects or other problems? Ultimately you may only find "concrete proof" by becoming your own test subject.