I was addicted to phenibut for - errrr I'm not sure. 9-12 months maybe? And while different in effects to pregabalin, but structurally very similar, I found zero cross tolerance with gabapetin. I used to switch to gabapentin for a good few days to allow phenibut tolerance to reduce substantially, but they are thought to act on different receptors entirely with gabapentin not quite being the gaba activator they initially thought and the pharmalogical profile quite uncertain. Interestingly what reduced my gabapentin tolerance after then taking shit loads of that for a time, was supplementing 400mg chelated magnesium at a time (not at the same time as gabapentin). This dropped my gabapentin doseage from my baseline of 4-5 x 300mg to 2-4 x 300mg.
I've actually found no phenibut (or gabapentin) cross tolerance with benzos either, or alcohol. Even with ridiculous benzo tolerance, 1200mg phenibut still works. But phenibuts absorption rate/bioavailability is obscure and inconsistently weird.
The trick to phenibut is an empty stomach, patience, and lots of caffeine/coffee. When I was taking phenibut breakfast just wasn't a thing, which is great for losing weight

. I've had it kick in fully after 30 minutes, mostly after 2 hours, sometimes 3-4 hours (common-ish), today I had some and it took 6 and a half hours (quite uncommon), and once I took some at 6am and it kicked in really hard at 4pm, ten hours later.
The effects are subtle but are basically:
-Mood enhancer (generally positive)
-Social enhancer
-Makes you horny
-Makes you have a good day
-No cognitive or memory impairment
-A sort of twingy feeling in the head, a bit like GHB or, less so, MDMA
It's definitely a drug, but the lack of impairment and generally subtle effects can make it seem unlike one. It's certainly unique. Totally unlike alcohol or benzos IME, like I've seen some claim.