Phenibut is as has been mentioned, a drug where one has to find their "sweet spot", which out of all of the other drugs I have tried truly seems to differ greatly from one person to the next. I've only been using phenibut off and on for maybe a little over a year now. At first I tried using phenibut from doses ranging from 1.5-2 grams every other day following the dosing guidelines provided by the vendor I was getting it from. This worked for a couple of weeks, but eventually a tolerance was noted and I had to step down.
I now take no more then 1.5 grams when I do take it, and no more then maybe three to four times per month. I have been dealing with some PAW after quitting diclazepam basically cold turkey after attempting to use it to come off a horrendous etizolam habit, and it does seem to help for a couple days. Diclazepam gave me a lot of unwanted side effects and put me in a horribly depressed state, which is why after titrating down rather quickly from a Benzo with such a long Half-Life I chose to jump off cold turkey at about 1 milligram and use etizolam once again when the withdraws became unbearable. This may sound crazy, perhaps it is, but it is working. Not that I would suggest anyone to follow suit. If you have health insurance then go see a doctor.
Anyway, phenibut really messed up my stomach when I was using it at the aforementioned doses in the first paragraph. And when I say messed up, I mean it felt as though I was burning a hole in my stomach lining. I chose to jump off of that train cold turkey as well, and the withdraw experienced only lasted maybe a week tops. Again, not suggesting anyone do this as it can be dangerous depending on what dose you have been taking and for how long, I just have come to the conclusion that as long as I am not in danger of seizing coming off of gabaergic drugs (been there done that), it is just easier for me to quit and have a couple of days/weeks of hell rather then to taper slowly and prolong the process. I also use various dissociatives to combat excitotoxicity when need be, which have proven for me to be nothing but beneficial. Again, don't do what I do if you have health insurance and can afford to see a doctor. My choices are my own based off of past and present experience. They work for me. YMMV
Phenibut is a strange drug, but I do benefit/enjoy it a lot so it has its place in my book when used very responsibly.