After getting several brands of PEA from Amazon US, where all of them weighed less than the advertised contents ( one was 300mg instead of 1600mg ) I did a fair bit of research on supplements . I have already posted versions of this before, but I cannot see any mentions here on sources, so it is probably worth repeating
As best I can tell at least half of what is sold on Amazon US as supplements is dodgy. If it is newer, more fashionable or more expensive, the odds are much worse, and probably a lot lower for basic vitamins. Mostly it is a case of getting less than you pay for, anything from 0% to 50% is common. A lot of the ads specify the size of the pill, and you can calculate how much will fit in a pill that size, and a lot of the time it just is not possible, so the fraud is deliberate and intentional.
The US lacks basic consumer health protection laws regarding supplements, so they can pretty much rip everyone off with no consequences. It is illegal to do that in Australia, and amazon au is better, but there are still plenty of dodgy ones.
If you are buying a lot of supplements , it is worth doing some research on what brands are good, and assume anything new, with a US website, with fancy packaging or claims like liposomal are dodgy. And anything that is a lot cheaper per gram of actual supplement is also dodgy. Iherb is a better option, with at least some products with some testing results though none are truly third party, most of the ones are I know are dodgy are not there, but there are still some that look suspicious.
Brands that are ok as in all or most tests are fine or at least reasonably close are NOW, vitacost, henry blooms, nutricost, neurogan, bulk supplements, best naturals, horbaach, vitamatic, source naturals, swanson, solgar, nutragold, sonora, kirkland, nootrpic depot, natrol, Jarrow Formulas, Thorne, Pure Encapsulations
This is not meant to be an exhaustive list, and a few of them had results of 70% or so in one test, but were mostly ok. Thanks to the company NOW for being honest and doing testing on their supplements and others and publishing the results rather than making twice as much money by ripping everyone off.