Any Gabaergic is gonna hit you hard when combined with another. Doesn't matter if one's Gaba-a and one's Gaba-b or even sodium channel for that matter. I also don't wanna preach, but be reeeally careful with phenibut, the effects aren't worth the withdrawals. If it was more like kava and you could have it daily without problems then it would be a godsend to people, but unfortunately tolerance develops to that stuff faster than anything on the planet it seems. Twice a week is the max with phenibut. I'd just stick with kava quite frankly. I've been down the phenibut magical yellow brick road and it ended up as a wasteland with a road strewn with glass. Anyways, you probably already know this, but thought I'd say it anyways. Even every other day you'll eventually start having increased anxiety and sleep problems on the off day. It's just not worth it. The half life is only 5 hours but there's gotta be other active metabolites that keep your Gaba-b's active because there's no other explanation for the rapid tolerance. And 500mg a day reduction isn't noticeable at first if your at, say 3 grams, but when you get down to 1 gram and then 500 and then none, your gonna feel it man. Then what? Benzo's? Check out "another phenibut casualty" on mindandmuscle.net...it's just not that easy. The longer your on it, the worse it's gonna be. It's not just one week of withdrawals and then your okay, it lasts much longer. Not benzo long, but long enough. Also, at higher amounts it starts hitting Gaba-a as well. Now your having to get Gaba-a back to normal as well as Gaba-b. Higher than that and it affects dopamine. You'll start to have to dose multiple times a day (if you don't already) because otherwise you can't sleep and get anxious at night. When you have to take large amounts in the evening as well, the dopamine will keep you up. It's gonna turn into a trainwreck dude, trust me. Better try to find an alternative, a kava that's uplifting and not too sedating, and get off now. You can't take it forever, that just doesn't happen. Last but not least, it's not gonna be legal much longer.