From personal experience, I can say that Phenibut is a fairly effective drug. I really liked Phenibut from the USA by SNS Smart Powders. I bought it without a prescription in sports nutrition. The dosage in capsules is 300 and 500 mg. Acts very gently and without drowsiness. If you buy, take it.
Persen and Negrustin are herbal medicine. There is no clinically reliable information (in other words, the answer to the question whether it really helps if it does not help) is absent. There is also not enough clinic for Phenibut. But in the Russian Federation, due to the lack of standards and protocols, doctors also use unproven medicine, indicating their personal clinical experience as criteria for reliability (you yourself understand the degree of scientific nature of the argument is very frivolous).