I've been using L-Theanine for a over a year now and then and it definitely has effects! I use it mostly for sleep 100-150mg in combination of 5HTP which I found it to be an incredible sleep cocktail. I generally don't have trouble sleeping but this cocktail gives me great dreams and increase the quality of my sleep where 6-7 hours is very much enough for me compared to the usual 8-9. Unsurprisingly, l-theanine is po…
Not to put too fine a point on it but if there are blind trials showing no effect and non-blind trials showing an effect, my conclusion would be the effect is a placebo.
Unfortunately, there isn't much regulation for supplements in general. Some companies do 3rd party purity testing, though it's not always the case.