I just recently bought some and started experimenting. Its pharmacology is most similar to baclofen (near identical I believe, except the dosage for phenibut is much higher) and also similar to Xyrem (phenibut is a gaba-b agonist with a long duration of effect).
I have noticed: It is much easier to fall asleep fast. Also it seems way easier to wake up, get up and get moving with energy. I have been taking 1.5-2 grams in the evening (since it takes 2-3 hours to really kick in) and it doesn't seem to suppress REM because I dream a ton and the dreams are enhanced.... but despite that I am able to fall asleep very fast and then wake up just a few hours later and get up and get going.It reminds me of baclofen years ago. Near identical effect.... I will warn people that baclofen and phenibut are pretty addictive if you take them everyday. Its a good idea to stock up if you do try to experiment so you don't run out and experience a withdrawal. I was dependent on baclofen over a decade ago and used phenibut when I ran out (and to taper off) and it really seems like the same drug effect wise. Phenibut is widely available pretty much all over the internet, and prices have come way down since years ago when I first tried it. Not sure if i'm going to take it daily, possibly not a good idea but I will experiment more. I like being able to lay down and pass out fast, and then get up when I want to get up with some energy. It seems to make transitioning from sleep/awake/sleep/etc easier like I have more control which is very nice.. Usually its very hard to get up. Phenibut is not "weak" like most supplements, it is just as hardcore as baclofen so if you experiment keep that in mind it is a "full complete drug" and not just some weak vitamin or useless supplement. Thought I would share this since people sometimes have a hard time getting balcofen and this is widely available.
From wikipedia: "Phenibut is a derivative of GABA with a phenyl group in the β-position. It is a chiral molecule and thus has two potential configurations, as (R)- and (S)-enantiomers. It has almost the same structure as baclofen (lacking only a chlorine atom in the para-position of the phenyl group) and contains phenethylamine in its structure. Pregabalin has a structure similar to phenibut, in which the phenyl group is substituted with an isobutyl group."
I did not know it was that closely related to Baclofen... Baclofen is basically 4-chloro-phenibut. I'm surprised I haven't seen anybody else mention it on here. I'm not sure how they get away with selling it but its been sold openly for over a decade and its much more widely available now. Same type of places that sell L-Citrulline type supplements have Phenibut